U.S. patent application number 16/248420 was filed with the patent office on 2019-05-30 for perovskite surface defect passivation using zwitterionic amino acids.
The applicant listed for this patent is NUtech Ventures. Invention is credited to Jinsong Huang, Dai Jun, Shuang Yang, Xiao Cheng Zeng.
Application Number | 20190164699 16/248420 |
Document ID | / |
Family ID | 63170710 |
Filed Date | 2019-05-30 |
View All Diagrams
United States Patent
Application |
20190164699 |
Kind Code |
A1 |
Zeng; Xiao Cheng ; et
al. |
May 30, 2019 |
PEROVSKITE SURFACE DEFECT PASSIVATION USING ZWITTERIONIC AMINO
ACIDS
Abstract
Semiconductor devices including a cathode layer, an anode layer,
an active layer disposed between the cathode layer and the anode
layer, wherein the active layer includes a perovskite layer, and a
passivation layer disposed directly on a surface of the active
layer between the cathode layer and the active layer, the
passivation layer including a zwitterionic amino acid, such as
valine or phenylalanine or other amino acid that passivates both
cationic and anionic defects in the surface of the active
layer.
Inventors: |
Zeng; Xiao Cheng; (Lincoln,
NE) ; Huang; Jinsong; (Chapel Hill, NC) ; Jun;
Dai; (Lincoln, NE) ; Yang; Shuang; (Chapel
Hill, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NUtech Ventures |
Lincoln |
NE |
US |
|
|
Family ID: |
63170710 |
Appl. No.: |
16/248420 |
Filed: |
January 15, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US2018/018706 |
Feb 20, 2018 |
|
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16248420 |
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62460266 |
Feb 17, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 51/0072 20130101;
H01L 51/442 20130101; H01L 51/448 20130101; H01L 2251/308 20130101;
H01G 9/0036 20130101; H01L 51/0077 20130101; H01L 51/0003 20130101;
H01L 51/424 20130101; H01G 9/2018 20130101; H01L 51/0035 20130101;
H01L 51/4253 20130101; H01L 51/0046 20130101; H01G 9/2059 20130101;
H01L 2251/301 20130101; H01G 9/2009 20130101 |
International
Class: |
H01G 9/20 20060101
H01G009/20; H01G 9/00 20060101 H01G009/00; H01L 51/00 20060101
H01L051/00; H01L 51/42 20060101 H01L051/42; H01L 51/44 20060101
H01L051/44 |
Goverment Interests
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was made with government support under
01A1538893 and DMR1420645 awarded by the National Science
Foundation and FA9550-16-1-0299 awarded by the Air Force Office of
Scientific Research. The government has certain rights in the
invention.
Claims
1. A semiconductor device, comprising: a cathode layer; an anode
layer; an active layer disposed between the cathode layer and the
anode layer, where the active layer includes a perovskite layer;
and a passivation layer disposed directly on a surface of the
active layer between the cathode layer and the active layer, the
passivation layer comprising a layer of material that passivates
both cationic and anionic defects in the surface of the active
layer, wherein the layer of material comprises a zwitterionic amino
acid.
2. The semiconductor device of claim 1, wherein the perovskite
layer includes organometal trihalide perovskite having the formula
ABX.sub.3, or A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion , B is a metal cation, and X is a halide
anion, thiocyanate (SCN-) or a mixture thereof.
3. The semiconductor device of claim 1, further comprising: a first
carrier transport layer disposed between the passivation layer and
the cathode; and a second carrier transport layer disposed between
the active layer and the anode, the first carrier transport layer
having a higher electron conductivity than the second carrier
transport layer, the second carrier transport layer having a higher
hole conductivity than the first carrier transport layer.
4. The semiconductor device of claim 3, wherein: the first carrier
transport layer comprises at least one C60, a fullerene, a
fullerene-derivative, LiF, CsF, LiCoO2, CS2CO3, TiOx, TiO2 nanorods
(NRs), ZnO, ZnO nanorods (NRs), ZnO nanoparticles (NPs), ZnO,
Al2O3, CaO, bathocuproine (BCP), copper phthalocyanine (CuPc),
pentacene, pyronin B, pentadecafluorooctyl phenyl-C60-butyrate
(F-PCBM), C60, C60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene
derivative (C-PCBSD), single walled carbon nanotubes (SWCNT),
poly(ethylene glycol) (PEG), Polyethylenimine (PEI),
poly(dimethylsiloxaneblock-methyl methacrylate) (PDMS-b-PMMA),
polar polyfluorene (PF-EP), polyfluorene bearing lateral amino
groups (PFN), polyfluorene bearing quaternary ammonium groups in
the side chains (WPF-oxy-F), polyfluorene bearing quaternary
ammonium groups in the side chains (WPF-6-oxy-F), fluorene
alternating and random copolymer bearing cationic groups in the
alkyl side chains (PFNBr-DBTI5), fluorene alternating and random
copolymer bearing cationic groups in the alkyl side chains
(PFPNBr), or poly(ethylene oxide) (PEO).; and the second carrier
transport layer comprises at least one
poly(3,4-ethylenedioxithiophene) (PEDOT) doped with poly(styrene
sulfonicacid) (PSS),
4,4'bis[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl
(TPD-Si2), poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60,
copper phthalocyanine (CuPc), poly[3,4-(1hydroxymethyl)
ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic
acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s,
poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI),
poly[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine]
(PFT), 4,4'bis[(p-trichlorosilylpropylphenyl)phenylamino] biphenyl
(TSPP), 5,5'-bis[(p-trichlorosilylpropylphenyl)
phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane,
3,3,3-trifluoropropyltrichlorosilane or
3-aminopropyltriethoxysilanePoly[bis(4-phenyl)(2,4,6-trimethylphenyl)amin-
e] (PTAA), V2O5, VOx, MoO3, WO3, ReO3, NiOx, AgOx/PEDOT:PSS, Cu2O,
CuSCN/P3HT, or Au nanoparticles.
5. The semiconductor device of claim 1, further comprising a
fullerene layer disposed on the passivation layer between the
passivation layer and the first carrier transport layer.
6. The semiconductor device of claim 5, wherein the fullerene layer
comprises a layer of C.sub.60 having a thickness of between about 1
nm and about 100 nm.
7. The semiconductor device of claim 1, wherein the anode layer
includes at least one of indium tin oxide (ITO), fluorine-doped tin
oxide (FTO), aluminum-doped zinc oxide (AZO), antimony-tin mixed
oxide (ATO), a conductive polymer, a network of metal nanowire, a
network of carbon nanowire, nanotube, nanosheet, nanorod, carbon
nanotube, silver nanowire, or graphene.
8. The semiconductor device of claim 1, wherein the cathode layer
includes at least one of copper, aluminum, calcium, magnesium,
lithium, sodium, potassium, strontium, cesium, barium, iron,
cobalt, nickel, silver, zinc, tin, samarium, ytterbium, chromium,
gold, graphene, an alkali metal fluoride, an alkaline-earth metal
fluoride, an alkali metal chloride, an alkaline-earth metal
chloride, an alkali metal oxide, an alkaline-earth metal oxide, a
metal carbonate, a metal acetate, or a combination of at least two
of the above materials.
9. The semiconductor device of claim 1, wherein the passivation
layer has a thickness of between about 1 nm and about 30 nm.
10. The semiconductor device of claim 1, wherein the zwitterionic
amino acid comprises one of valine or phenylalanine.
11. A semiconductor device, comprising: a cathode layer; an anode
layer; an active layer disposed between the cathode layer and the
anode layer, where the active layer includes an organometal
trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), an alkali metal ion or formamidinium
(H.sub.2NCHNH.sub.2.sup.+), B is a metal cation, and X is a halide
anion, thiocyanate (SCN-) or a mixture thereof; a passivation layer
disposed directly on a surface of the active layer between the
cathode layer and the active layer, the passivation layer
comprising a layer of material that passivates both cationic and
anionic defects in the surface of the active layer, wherein the
layer of material comprises a zwitterionic amino acid; an electron
extraction layer disposed directly on the passivation layer between
the passivation layer and the cathode layer, the electron
extraction layer comprising a layer of C.sub.60; a first carrier
transport layer comprising bathocuproine (BCP) and disposed between
the electron extraction layer and the cathode; and a second carrier
transport layer comprising
Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and disposed
between the active layer and the anode.
12. The semiconductor device of claim 11, wherein the anode layer
includes indium tin oxide (ITO) and wherein the cathode layer
includes copper.
13. The semiconductor device of claim 11, wherein the layer of
C.sub.60 has a thickness of between about 1 nm and about 100
nm.
14. The semiconductor device of claim 11, wherein the active layer
has a thickness of between about 1 nm and about 10 .mu.m.
15. The semiconductor device of claim 11, wherein the passivation
layer has a thickness of between about 1 nm and about 30 nm.
16. The semiconductor device of claim 11, wherein the zwitterionic
amino acid comprises one of valine or phenylalanine.
17. A method of making a semiconductor device, the process
comprising: providing an active layer, where the active layer
includes a perovskite material; and applying a passivation layer
directly on a surface of the active layer, the passivation layer
comprising a first material that passivates both cationic and
anionic defects in the surface of the active layer, wherein the
first material comprises a zwitterionic amino acid.
18. The method of claim 17, further comprising forming a cathode
layer on the passivation layer.
19. The method of claim 18, further comprising forming an anode
layer on a side of the active layer so that the active layer is
disposed between the cathode layer and the anode layer.
20. The method of claim 19, further comprising forming a first
carrier transport layer disposed between the passivation layer and
the cathode layer; and forming a second carrier transport layer
disposed between the active layer and the anode layer, the first
carrier transport layer having a higher electron conductivity than
the second carrier transport layer, the second carrier transport
layer having a higher hole conductivity than the first carrier
transport layer.
21. The method of claim 17, wherein the perovskite material
includes organometal trihalide perovskite having the formula
ABX.sub.3, or A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion , B is a metal cation, and X is a halide
anion, thiocyanate (SCN-) or a mixture thereof.
22. The method of claim 17, wherein the zwitterionic amino acid
comprises one of valine or phenylalanine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present Application for Patent is a continuation-in part
of, and claims priority to, U.S. International Patent Application
No. PCT/US2018/018706 by Huang et al., entitled "Passivation of
Defects in Perovskite Materials For Improved Solar Cell Efficiency
and Stability," filed Feb. 20, 2018, which claims the benefit of
U.S. Provisional Patent Application No. 62/460,266, filed Feb. 17,
2017, entitled "Passivation of Defects in Perovskite Materials For
Improved Solar Cell Efficiency and Stability," each of which is
incorporated in its entirety herein by reference.
BACKGROUND AND SUMMARY
[0003] The present disclosure generally provides photodetector
systems and methods, and more particularly photodetector systems
and methods including perovskite photoactive or photoresponsive
materials.
[0004] The ionic defects at the surfaces and grain boundaries of
organic-inorganic halide perovskites (OIHPs) films are detrimental
to both the efficiency and stability of OIHP devices such as solar
cells. There are both negatively and positively charged defects in
ionic OIHPs, while generally only one type of the defects is
passivated. In certain embodiments, quaternary ammonium halides
(QAHs), which are B-complex vitamins, are used to effectively
passivate both cationic and anionic defects of OIHPs with negative-
and positive-charged components, respectively. The dual-defect
passivation advantageously reduces the charge trap density and
elongates the carrier recombination lifetime. The dual-defect
passivation also advantageously increases open-circuit-voltage of
the device with bandgap of 1.55 eV to 1.15 V, and boosts the
efficiency to 21.0%. QAHs universally passivate other types of
OIHPs with bandgaps ranging from 1.51 eV to 1.72 eV and
advantageously increase efficiency by 10-35%. Moreover, the defect
healing also significantly enhances the stability of OIHP films.
The various embodiments provide a new paradigm for defects
passivation to further improve both the efficiency and stability of
OIHPs devices such as solar cells.
[0005] According to an embodiment, a semiconductor device is
provided that typically includes a cathode layer, an anode layer,
an active layer disposed between the cathode layer and the anode
layer, wherein the active layer includes a perovskite layer, and a
passivation layer disposed directly on a surface of the active
layer between the cathode layer and the active layer, the
passivation layer comprising a layer of material that passivates
both cationic and anionic defects in the surface of the active
layer. In certain aspects, the perovskite layer includes
organometal trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion (e.g., Cs.sup.+, Rb.sup.+), B is a metal
cation, and X is a halide anion (e.g., Cl, Br, I), thiocyanate
(SCN-) or a mixture thereof. In certain aspects, the layer of
material comprises a quaternary ammonium halide (QAH). In certain
aspects, the layer of material comprises a zwitterion molecule. In
certain aspects, the layer of material comprises a choline
zwitterion molecule. In certain aspects, the layer of material
comprises a zwitterionic amino acid. In certain aspects, the
zwitterionic amino acid comprises one of valine or phenylalanine.
In certain aspects, the semiconductor device further includes a
first carrier transport layer disposed between the passivation
layer and the cathode; and a second carrier transport layer
disposed between the active layer and the anode, the first carrier
transport layer having a higher electron conductivity than the
second carrier transport layer, the second buffer layer having a
higher hole conductivity than the first buffer layer.
[0006] According to another embodiment, a semiconductor device is
provided that typically includes a cathode layer, an anode layer,
and an active layer disposed between the cathode layer and the
anode layer, wherein the active layer includes an organometal
trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium (CH.sub.3NH.sub.3+),
an alkali metal ion (e.g., Cs.sup.+, Rb.sup.+) or formamidinium
(H.sub.2NCHNH.sub.2.sup.+), B is a metal cation, and X is a halide
anion(e.g., Cl, Br, I), thiocyanate (SCN-) or a mixture thereof.
The semiconductor device also typically includes a passivation
layer disposed directly on a surface of the active layer between
the cathode layer and the active layer, the passivation layer
including a layer of material that passivates both cationic and
anionic defects in the surface of the active layer. In certain
aspects, the layer of material comprises a zwitterionic amino acid.
In certain aspects, the zwitterionic amino acid comprises one of
valine or phenylalanine. The semiconductor device further typically
includes an electron extraction layer disposed directly on the
passivation layer between the passivation layer and the cathode
layer, the electron extraction layer comprising a layer of
C.sub.60, a first charge transport layer comprising bathocuproine
(BCP) and disposed between the electron extraction layer and the
cathode, and a second charge transport layer comprising Poly
[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and disposed
between the active layer and the anode. In certain aspects, the
layer of C60 has a thickness of between about 1 nm and about 100
nm.
[0007] According to yet another embodiment, a method of making or
of forming a semiconductor device is provided. The process
typically includes providing an active layer, wherein the active
layer includes a perovskite material, and applying a passivation
layer directly on a surface of the active layer, the passivation
layer comprising a first material that passivates both cationic and
anionic defects in the surface of the active layer. In certain
aspects, the method also typically includes forming a cathode layer
on the passivation layer. In certain aspects, the method also
typically includes forming an anode layer on a side of the active
layer so that the active layer is disposed between the cathode
layer and the anode layer. In certain aspects, the method also
typically includes forming a first carrier transport layer disposed
between the passivation layer and the cathode layer, and forming a
second carrier transport layer disposed between the active layer
and the anode layer, the first carrier transport layer having a
higher electron conductivity than the second carrier transport
layer, the second carrier transport layer having a higher hole
conductivity than the first carrier transport layer. In certain
aspects, the first material comprises a quaternary ammonium halide
(QAH) or a zwitterion molecule. In certain aspects, the layer of
material comprises a zwitterionic amino acid. In certain aspects,
the zwitterionic amino acid comprises one of valine or
phenylalanine. In certain aspects, the perovskite material includes
organometal trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion , B is a metal cation, and X is a halide
anion, thiocyanate (SCN-) or a mixture thereof.
[0008] According to a further embodiment, a semiconductor device is
provided that typically includes a cathode layer, an anode layer,
an active layer disposed between the cathode layer and the anode
layer, wherein the active layer includes a perovskite layer, and a
passivation layer disposed directly on a surface of the active
layer between the cathode layer and the active layer, the
passivation layer comprising a zwitterionic amino acid that
passivates both cationic and anionic defects in the surface of the
active layer. In certain aspects, the perovskite layer includes
organometal trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion (e.g., Cs.sup.+, Rb.sup.+), B is a metal
cation, and X is a halide anion (e.g., Cl, Br, I), thiocyanate
(SCN-) or a mixture thereof. In certain aspects, the zwitterionic
amino acid comprises one of valine or phenylalanine.
[0009] For the various semiconductor devices, and formation
processes, in certain aspects, the anode layer includes indium tin
oxide (ITO) and the cathode layer includes copper. In certain
aspects, the active layer has a thickness of between about 1 nm and
about 10 .mu.m. In certain aspects, the passivation layer has a
thickness of between about 1 nm and about 30 nm.
[0010] Reference to the remaining portions of the specification,
including the drawings and claims, will realize other features and
advantages of the present invention. Further features and
advantages of the present invention, as well as the structure and
operation of various embodiments of the present invention, are
described in detail below with respect to the accompanying
drawings. In the drawings, like reference numbers indicate
identical or functionally similar elements.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0011] The detailed description is described with reference to the
accompanying FIG.s. The use of the same reference numbers in
different instances in the description and the FIG.s may indicate
similar or identical items.
[0012] FIGS. 1A and 1B show embodiments of device structures of
organic-inorganic halide perovskite (OIHP) devices.
[0013] FIG. 2 shows the passivation mechanism by quaternary
ammonium halides (QAHs). The quaternary ammonium ions are expected
to only passivate MA.sup.+ vacancies by occupying cuboctahedral
sites to compensate the MA.sup.+ loss on the film surfaces, and the
halide vacancies are compensated by additional halide ions from
QAHs.
[0014] FIG. 3 shows trap density of states (tDOS) obtained by
thermal admittance spectroscopy for devices with PCBM and Choline
chloride passivation layers.
[0015] FIG. 4A shows current density-voltage (J-V) characteristics
of two-step processed MAPbI.sub.3 devices with different
passivation layers.
[0016] FIG. 4B shows J-V curves for the two-step processed
MAPbI.sub.3 devices passivated by choline chloride and choline
iodide.
[0017] FIG. 4C shows statistics of V.sub.OC distribution for
devices with PCBM, L-.alpha.-Phosphatidylcholine, Choline iodide,
and Choline chloride, where solid lines represent the Gauss
distribution fitting for the statistic of V.sub.OC.
[0018] FIGS. 5A-5D show stability assessment of perovskite solar
cells with different passivation layers: Evolution of PCE (FIG.
5A), J.sub.SC (FIG. 5B), V.sub.OC (FIG. 5C), and FF (FIG. 5D)
relative to the initial parameters for the device over 35 days of
storage in air. Each average (symbol) and standard deviation (error
bar) was calculated from three solar cells. The initial efficiency
is 19.5% and 20.1% for devices with L-.alpha.-Phosphatidylcholine,
Choline chloride, respectively.
[0019] FIG. 5E shows photographic images of the OIHP films with
different treatments. The first and second rows show the images of
the pristine films, with L-.alpha.-Phosphatidylcholine, and with
Choline chloride from left to right, respectively, before after
exposure to humidity of 90.+-.5% for 2.5 h (the size of the film is
15 mm).
[0020] FIG. 6A shows a schematic of normal and zwitterionic forms
of amino acids according to an embodiment.
[0021] FIG. 6B show a slab model of clean PbI.sub.2-terminated
MAPbI.sub.3.
[0022] FIG. 6C shows calculated transition levels (q'/q) of
intrinsic acceptors on MAPbI.sub.3 surface.
[0023] FIG. 6D shows calculated transition levels (q'/q) of
intrinsic donors on MAPbI.sub.3 surface.
[0024] FIG. 6E shows the structure of valine and phenylalanine.
[0025] FIG. 6F shows I interstitial defects on a 9-layer
PbI.sub.2-terminated MAPbI.sub.3 surface.
[0026] FIG. 6G shows Pb interstitial defects on a 9-layer
PbI.sub.2-terminated MAPbI.sub.3 surface.
[0027] FIG. 6H shows Pb.sub.2 interstitial defects on a 9-layer
PbI.sub.2-terminated MAPbI.sub.3 surface.
[0028] FIG. 7A shows a schematic diagram of zwitterionic amino
acids passivation of perovskite surface defects according to an
embodiment.
[0029] FIG. 7B shows calculated transition levels (q'/q) of I.sub.i
and Pb.sub.i after valine and phenylalanine passivation according
to an embodiment.
[0030] FIG. 8 shows in panels a)-c) density of states (DOS) for
MAPbI.sub.3 surface with Pb interstitial defects, charge density of
the highest occupied band (HOB) for unpassivated MAPbI.sub.3
surface with Pb interstitial defects, and charge density of HOB for
passivated MAPbI.sub.3 surface with Pb interstitial defects,
respectfully, and in panels d)-f) DOS for MAPbI.sub.3 surface with
Pb.sub.2 interstitial defects, charge density of the highest
occupied band (HOB) for unpassivated MAPbI.sub.3 surface with
Pb.sub.2 interstitial defects, and charge density of HOB for
passivated MAPbI.sub.3 surface with Pb.sub.2 interstitial defects,
respectfully, and in panels g)-i), DOS for MAPbI.sub.3 surface with
I interstitial defects, charge density of the highest occupied band
(HOB) for unpassivated MAPbI.sub.3 surface with I interstitial
defects, and charge density of HOB for passivated MAPbI.sub.3
surface with I interstitial defects, respectfully
[0031] FIG. 9A shows a device structure of a perovskite planar
heterojunction solar cell including an amino acid passivation layer
according to an embodiment.
[0032] FIG. 9B shows current density-voltage (J-V) characteristics
of two-step-processed devices with different passivation layers,
PCBM (control), phenylalanine (black), valine (blue).
[0033] FIG. 9C shows statistics of V.sub.OC distribution for
devices with valine (black), phenylalanine (red) and PCBM
(green).
[0034] FIG. 9D shows trap density of states obtained by thermal
admittance spectroscopy for devices with PCBM (blue), valine
(yellow) and phenylalanine (red).
DETAILED DESCRIPTION
[0035] The history of power conversion efficiency (PCE) enhancement
for thin-film and polycrystalline photovoltaic cells has witnessed
the importance of reducing charge recombination loss both inside
the photoactive layer and at the electrode contacts. Passivation of
defects at the film surface becomes critical when the charge
recombination inside the photoactive layer is negligible, which is
the case for the organic-inorganic halide perovskite (OIHP) devices
such as solar cells. Solution-processed OIHP devices embrace many
intriguing optoelectronics attributes, such as strong light
absorption, high charge carrier mobility, and long intrinsic
carrier recombination lifetime. The insensitivity to point defects
and easy crystallization of OIHP materials give rise to negligible
charge recombination in perovskite polycrystalline thin films.
However, the much shorter measured photoluminescence (PL)
recombination lifetime of the polycrystalline films than the
intrinsic carrier recombination lifetime from a single crystal
interior indicates there is still high density of defects at the
surface and grain boundaries of polycrystalline grains which are
not benign electronically. These defects originate most likely from
the low thermal stability, or low formation energy of OIHP
materials containing organic components which tends to easily
evaporate away from the surface during the thermal annealing
process. These surface and grain boundary (GB) defects may not
dramatically reduce device photocurrent output, because a portion
of the trapped charges may still escape over a long time and be
collected by the electrodes, as evidenced by the relative large
short circuit current (J.sub.SC) of many non-optimized devices,
while they would significantly impact open circuit voltage
(V.sub.OC) of the devices due to their energy disorder and reduced
carrier concentration which pull down the quasi-Fermi level
splitting. In addition, these defects can cause other device
instability issues, including ion migration and associated current
hysteresis, and device degradation in ambient environment. A recent
study of moisture dependent perovskite grain stability showed that
the degradation of perovskite grains was initialized by the
defective surface and GBs, while some single crystals with low
surface defect density and no GBs could be stable in air for
several years. The ionic defects (e.g., iodine or methylammonium
vacancies) in the polycrystalline film have small migration
activation energy (e.g., <0.1 eV) under 1 sun illumination. The
defects could also initialize the permeation of moisture or oxygen
into the perovskite films to accelerate the degradation of
perovskite devices. Thus, it is desirable to electronically
passivate the defects at the surface and GB to boost the PCE, and
to heal these defects to prolong the durability of OIHP
devices.
[0036] The ionic nature of OIHP materials imposes different
requirements for the defects passivation with covalent-bonding
semiconductors such as silicon (Si). The passivation of Si is
mainly achieved by the elimination of the Si dangling bonds by
formation of Si--O, Si--N or Si--H covalent bonds, which is however
not applicable to strong ionic OIHPs. So far different passivation
molecules have been reported to perform as electron donors or
electron acceptors that can interact with the charged defects of
OIHPs, and thereafter annihilate the relevant defect-induced charge
traps. Lewis acids, such as phenyl-C61-butyric acid methyl ester
(PCBM), as the good electron transporting materials could accept an
electron from the negative charged Pb-I antisite defects,
Pbl.sub.3.sup.- or under-coordinated halide ions and thus passivate
the halide-induced deep traps. Lewis base molecules, such as
thiophene or pyridine, usually perform as the electron donors which
could bind to the positively charged, under-coordinated Pb.sup.2+
ions. However, these molecules could only passivate one type of
defects, either positive charged or negative charged defects, but
not both together. The defects in OIHP materials are charged,
either positively or negatively, and therefore the passivation of
them should take the charge neutrality into consideration.
[0037] In certain embodiments, a system of materials, including
quaternary ammonium halides (QAHs), are used to passivate both
cationic and anionic defects in OIHP with its negative- and
positive-charged components. The dual-modality passivation
remarkably reduces the trap density and prolongs the carrier
lifetime, which universally enhances the V.sub.OC of the OIHP
planar heterojunction devices with different bandgaps and
consequently increases the PCE by 10%-35%. This strategy can also
enhance the stability of OIHPs devices, with almost no efficiency
loss after 800 h of storage in ambient condition. The general rules
for the passivation of ionic OIHPs include: the molecules or ions
should have similar size with that of the ionic defects, and the
molecules should have positive or negative charged components for
self-assembling with the charged defects. These results highlight
the importance of all-round passivation of charged ionic defects
for improvement of the efficiency and durability of OIHPs
devices.
[0038] Methods
[0039] Perovskite material layers are formed, e.g. a two-step
method may be used to make MAPbI.sub.3 films, e.g., fabricated by a
thermal annealing-induced interdiffusion method. See, e.g., U.S.
Pat. No. 9,391,287, which is hereby incorporated by reference in
its entirety. Perovskite materials may also be formed using a
one-step, solvent engineering method, e.g., as described in Jeon,
N. J. et al., "Solvent Engineering for High performance
Inorganic-Organic Hybrid Perovskite Solar Cells," Nat. Mater. 13,
897-903 (2014), which is incorporated by reference. The hole
transport layer (HTL)
poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) with
concentration of 2 mg/ml dissolved in toluene were spin coated at
the speed of 6,000 r.p.m for 35 s and then annealed at 100.degree.
C. for 10 min. PbI2 beads (99.999% trace metals basis) were
purchased from Sigma-Aldrich. After dissolved in
N,N-Dimethylformamide (DMF) at temperature of 100.degree. C.,
around 50 .mu.l of hot (-90 .degree. C.) 630 mg/ml PbI.sub.2 DMF
precursor solutions was quickly dropped onto the substrate and spin
coated at the speed of 6,000 r.p.m. The as-fabricated PbI.sub.2
films were dried and annealed at 90.degree. C. for 10 min. After
the PbI.sub.2 films cooled to 70.degree. C., 60 .mu.l of 63 mg/ml
methylammonium iodide (MAI) 2-propanol (IPA) precursor solution at
the temperature of 70.degree. C. was spun on the PbI.sub.2 films.
Subsequently, the sample was annealed at 70.degree. C. for 20 min
and 100.degree. C. for 60 min. During the thermal annealing
process, around 10 p.1 of DMF was added to the edge of the petri
dish when the temperature reached 100.degree. C.
[0040] The functional layer was applied to or disposed on the
perovskite material layer (active layer). For example, the
functional layer may be coated onto the perovskite substrate by
spin coating, e.g., at 4,000 r.p.m. for 35 s, and annealing, e.g.,
at 100.degree. C. for 30 min. The devices were finished by
disposing or applying other layers thereto, e.g., thermally
evaporating additional layers thereon, such as C.sub.60 (23 nm),
BCP (8 nm) and copper (80 nm) in sequential order.
[0041] FIG. 1A illustrates a device structure of an OIHP
photodetector device 1 according to an embodiment. As shown, device
1 includes a cathode layer 10, an anode layer 20, and an active
layer 30 disposed between the cathode layer 10 and the anode layer
20. Device 1 also includes a passivation layer 40 disposed directly
on a surface of the active layer between the active layer 30 and
the cathode layer 10. The passivation layer 30 includes a layer of
material that passivates both cationic and anionic defects in the
surface of the active layer as discussed herein. The passivation
layer 40 should generally have a thickness of between about 1 nm
and about 30 nm or more, depending on the specific application. The
active layer 30 in an embodiment includes a layer of perovskite
material, where the perovskite material includes organometal
trihalide perovskite having the formula ABX.sub.3, or
A.sub.2BX.sub.4, wherein A is methylammonium
(CH.sub.3NH.sub.3.sup.+), formamidinium (H.sub.2NCHNH.sub.2.sup.+),
or an alkali-metal ion (e.g., Cs.sup.+, Rb.sup.+), B is a metal
cation, and X is a halide anion (e.g., Cl, Br, or I), thiocyanate
(SCN-) or a mixture thereof. For example, in an embodiment, active
layer 30 may include an organometal trihalide perovskite having the
formula FA.sub.xMA.sub.1-xBX.sub.3 where FA is formamidinium
(H.sub.2NCHNH.sub.2.sup.+), and MA is methylammonium
(CH.sub.3NH.sub.3.sup.+) and x is a fractional value between (and
including) 0 and 1. In an embodiment, X may be a mixture of two or
more halides. For example, the active layer 40 may include
FA.sub.xMA.sub.1-xB(Br.sub.1-yI.sub.y).sub.3 where y is a
fractional value between (and including) 0 and 1 and where x may
have the same value of y or a different value. Specific examples
might include FA.sub.0.85MA.sub.0.15B(Br.sub.0.15I.sub.0.85).sub.3,
FA.sub.0.83MA.sub.0.17B(Br.sub.0.17I.sub.0.83).sub.3, and
FA.sub.0.83MA.sub.0.17B(Br.sub.0.4I.sub.0.6).sub.3. The active
layer 30 should generally have a thickness of between about 1 nm
and about 10 .mu.m depending on the specific application. For
example, for typical photodetection applications, a perovskite
active layer will have a thickness of about 100 nm to about 2
.mu.m. Additionally, the active layer 30 should generally have an
active device area e.g., the cross-sectional light-capturing area,
of between about 0.04 mm.sup.2 to about 7 mm.sup.2, where a smaller
active area may be more desirable as will be discussed below.
[0042] The anode layer 20 and the cathode layer 10 generally
include conductive materials suited for the particular application.
Useful materials for the anode layer 20 includes indium tin oxide
(ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide
(AZO), antimony-tin mixed oxide (ATO), a conductive polymer, a
network of metal nanowire, a network of carbon nanowire, nanotube,
nanosheet, nanorod, carbon nanotube, silver nanowire, or graphene.
Useful materials for the cathode layer include copper, aluminum,
calcium, magnesium, lithium, sodium, potassium, strontium, cesium,
barium, iron, cobalt, nickel, silver, zinc, tin, samarium,
ytterbium, chromium, gold, graphene, an alkali metal fluoride, an
alkaline-earth metal fluoride, an alkali metal chloride, an
alkaline-earth metal chloride, an alkali metal oxide, an
alkaline-earth metal oxide, a metal carbonate, a metal acetate, or
a combination of at least two of the above materials.
[0043] FIG. 1B illustrates a perspective view of a specific device
structure of an OIHP photodetector device 100 according to an
embodiment. The specific structure of device 100 is composed of
anode 20 including conductive layer 24: e.g., indium tin oxide
(ITO) and second buffer layer 22: e.g.,
poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA)/active layer
30: e.g., CH.sub.3NH.sub.3PbI.sub.3(MAPbI.sub.3)/functional layer
40/and cathode layer 10 including electron extraction layer 12:
e.g., fullerene, C.sub.60, first buffer layer 14: e.g.,
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and conductive
material layer 16: e.g., Copper(Cu). As shown, the electron
extraction layer 12 includes only fullerene (C.sub.60), but may
include a combination of material layers, such as a
phenyl-C61-butyric acid methyl ester (PC.sub.61BM)/C.sub.60 double
layer. In this embodiment, the functional layer 40 is disposed
directly on the organic-inorganic halide perovskite (OIHP) film 30
to passivate of the ionic defects of the perovskite film to enhance
both the performance and the stability of the OIHP device.
[0044] In device 100, cathode layer 10 further includes an electron
extraction layer 12 disposed between the cathode material layer 16
and the active layer 30. The electron extraction layer 12, in one
embodiment, includes a layer of fullerene such as C.sub.60 directly
disposed on the passivation layer 40.
[0045] Cathode layer 10 optionally includes a first charge
transport layer 14 disposed between the electron extraction layer
12 and the cathode material layer 16. Anode layer 20 optionally
includes a second charge transport layer 22 disposed between the
active layer 30 and the anode material layer 24. When present, the
first charge transport layer 14 should have a higher electron
conductivity than the second charge transport layer 22, and the
second charge transport layer 22 should have a higher hole
conductivity than the first charge transport layer 14, e.g., the
first transport layer 14 acts as an electron transport layer (ETL)
and the second charge transfer layer 22 acts as a hole transport
layer (HTL).
[0046] In certain embodiments, the first charge transport layer 14
includes at least one of C.sub.60, a fullerene, a
fullerene-derivative, LiF, CsF, LiCoO.sub.2, CS.sub.2CO.sub.3,
TiOx, TiO.sub.2 nanorods (NRs), ZnO, ZnO nanorods (NRs), ZnO
nanoparticles (NPs), ZnO, Al.sub.2O.sub.3, CaO, bathocuproine
(BCP), copper phthalocyanine (CuPc), pentacene, pyronin B,
pentadecafluorooctyl phenyl-C.sub.60-butyrate (F-PCBM),
C.sub.60/LiF, ZnO NRs/PCBM, ZnO/cross-linked fullerene derivative
(C-PCBSD), single walled carbon nanotubes (SWCNT), poly(ethylene
glycol) (PEG), Polyethylenimine (PEI),
poly(dimethylsiloxaneblock-methyl methacrylate) (PDMS-b-PMMA),
polar polyfluorene (PF-EP), polyfluorene bearing lateral amino
groups (PFN), polyfluorene bearing quaternary ammonium groups in
the side chains (WPF-oxy-F), polyfluorene bearing quaternary
ammonium groups in the side chains (WPF-6-oxy-F), fluorene
alternating and random copolymer bearing cationic groups in the
alkyl side chains (PFNBr-DBTI5), fluorene alternating and random
copolymer bearing cationic groups in the alkyl side chains
(PFPNBr), or poly(ethylene oxide) (PEO). Representative fullerene
groups include C.sub.60, C70, C71, C76, C78, C80, C82, C84, and
C92. C.sub.60 derivative is at least one C.sub.60 derivative
selected from the group consisting of C.sub.60PCBM, bis-adduct
C.sub.60PCBM, tris-adduct C.sub.60PCBM, tetra-adduct C.sub.60PCBM,
penta-adduct C.sub.60PCBM, hexa-adduct C.sub.60PCBM, C.sub.60ThCBM,
bis-adduct C.sub.60ThCBM, tris-adduct C.sub.60ThCBM, tetra-adduct
C.sub.60ThCBM, penta-adduct C.sub.60ThCBM, hexa-adduct
C.sub.60ThCBM, C.sub.60 mono-indene adduct, C.sub.60 bis-indene
adduct, C.sub.60 tris-indene adduct, C.sub.60 tetra-indene adduct,
C.sub.60 penta-indene adduct, C.sub.60 hexa-indene adduct, C.sub.60
mono-quinodimethane adduct, C.sub.60 bis-quinodimethane adduct,
C.sub.60 tris-quinodimethane adduct, C.sub.60 tetra-quinodimethane
adduct, C.sub.60 penta-quinodimethane adduct, C.sub.60
hexa-quinodimethane adduct, C.sub.60 mono-(dimethyl
acetylenedicarboxylate) adduct, C.sub.60 bis-(dimethyl
acetylenedicarboxylate) adduct, C.sub.60 tris-(dimethyl
acetylenedicarboxylate) adduct, C.sub.60 tetra-(dimethyl
acetylenedicarboxylate) adduct, C.sub.60 penta-(dimethyl
acetylenedicarboxylate) adduct, C.sub.60 hexa-(dimethyl
acetylenedicarboxylate) adduct, and a mixture thereof. C70 and C84
derivatives include PC70BM, IC70BA, and PC84BM.
[0047] In certain embodiments, the second charge transport layer 22
includes at least one of poly(3,4-ethylenedioxithiophene) (PEDOT)
doped with poly(styrene sulfonicacid) (PSS), 4,4' bis
[(ptrichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si2),
poly(3-hexyl-2,5-thienylene vinylene) (P3HTV) and C60, copper
phthalocyanine (CuPc), poly[3,4-(lhydroxymethyl)
ethylenedioxythiophene] (PHEDOT), n-dodecylbenzenesulfonic
acid/hydrochloric acid-doped poly(aniline) nanotubes (a-PANIN)s,
poly(styrenesulfonic acid)-graft-poly(aniline) (PSSA-g-PANI), poly
[(9,9-dioctylfluorene)-co-N-(4-(1-methylpropyl)phenyl)diphenylamine]
(PFT), 4,4' bis [(p-trichlorosilylpropylphenyl)phenylamino]
biphenyl (TSPP), 5,5'-bis[(p-trichlorosilylpropylphenyl)
phenylamino]-2,20-bithiophene (TSPT), N-propyltriethoxysilane,
3,3,3 -trifluoropropyltrichlorosane or
3-aminopropyltriethoxysilanePoly
[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), V2O5, VOx,
MoO3, WO3, ReO3, NiOx, AgOx/PEDOT:PSS, Cu2O, CuSCN/P3HT, or Au
nanoparticles.
[0048] Functional layer 40 may include one or more different
structured molecules with varied functional groups, including, for
example, phenyl-C61-butyric acid methyl ester (PCBM),
L-.alpha.-Phosphatidylcholine, Tween-20,
Polyethylene-block-poly(ethylene glycol) (PE-PEG), Choline
chloride, and/or Choline iodide. In certain embodiments, the
functional layer includes a QAH having a structure of
NR.sub.4.sup.+X.sup.-, where R is an alkyl or aryl group and X is a
halide.
[0049] FIG. 4A shows the current density-voltage (J-V) curves of
the MAPbI.sub.3 (active layer) devices with deposition of different
functional/passivation layers. The control device with PCBM layer
showed typical performance with a short circuit current density
(J.sub.SC) of 22.5 mAcm.sup.-2, a V.sub.OC of 1.04 V, a fill factor
(FF) of 73.0%, and a PCE of 17.1%. Compared to the device with PCBM
layers, the performances of the MAPbI.sub.3 devices with Tween, and
PE-PEG buffer layers were even worse with maximum PCE between 13.6%
and 15.5%, even after optimization of the concentration of Tween
and PE-PEG solution. It indicates that Tween and PE-PEG cannot
passivate the surface defects on MAPbI.sub.3. In striking contrast,
the devices with L-.alpha.-Phosphatidylcholine layer showed a
significantly improved performance with an average J.sub.SC of 22.7
mA cm.sup.-2, V.sub.OC of 1.08 V, FF of 80.0%, and PCE of 19.6%.
The performance enhancement and hysteresis-free behavior were
tentatively attributed to the passivation effect of
L-.alpha.-Phosphatidylcholine molecules.
[0050] In comparison to Tween and PE-PEG,
L-.alpha.-Phosphatidylcholine has the same long alkyl chain, while
the difference is that L-.alpha.-Phosphatidylcholine has a choline
phosphate zwitterion structure. The zwitterion structure with the
choline group most likely passivates MAPbI.sub.3. To verify, two
other choline zwitterion molecules, also known as quaternary
ammonium halides (QAHs), including choline iodide and choline
chloride which have no long alkyl chain, were used as the
interfacial layer. As shown in FIG. 4B, the V.sub.OC of the
perovskite devices was significantly increased by choline iodide
and choline chloride as passivation layers without sacrificing the
J.sub.SC and FF of the devices, which confirmed the speculation.
The devices with choline iodide and choline chloride showed higher
V.sub.OC of 1.14 and 1.15 V. Consequently, PCEs of the
CH.sub.3NH.sub.3PbI.sub.3 devices with choline iodide and choline
chloride passivation layers were increased to 20.1%, and 20.0%,
respectively. FIG. 4C shows the V.sub.OC distribution of the
devices with different passivation layers. The average V.sub.OC
values are 1.04, 1.09, 1.13, and 1.13 V for the statistic V.sub.OC
of the devices with PCBM, L-.alpha.-Phosphatidylcholine, choline
iodide and choline chloride, respectively. The larger average
V.sub.OC of the devices passivated by QAHs than by
L-.alpha.-Phosphatidylcholine indicates there is an additional
passivation effect from the halide ions, because both of them have
the quaternary ammonium component. There are both
positively-charged cationic and negatively-charged anionic defects
in OIHPs, such as I.sup.- and MA.sup.+ vacancies, respectively,
while quaternary ammonium ions are expected to only passivate
MA.sup.+ vacancies by occupying cuboctahedral sites to compensate
the MA.sup.+ loss on the film surfaces, as illustrated in FIG. 2.
Loss of halide ions by the evaporation of MAI during thermal
annealing process needs to be compensated by additional halide
ions. Therefore, the dual passivation effect is critical in
achieving the high efficiency devices according to various
embodiments herein. The notable better passivation effect of
choline chloride than choline iodide can be explained by the
stronger Pb--Cl bonding than Pb--I bond, and small amount of Cl
addition has been broadly reported to enhance the charge
recombination lifetime in MAPbI.sub.3. Based on the mechanism of
passivation presented herein, any Zwitterion molecular structure
should have a good passivation effect, because they have both
negative and positive electric charges. A Zwitterion molecule may
passivate both cationic and anion defects if the spacing of these
defects is similar to or the same as the size of the Zwitterion
molecule. However, the defects at the surface of perovskite films
may have a very complicated distribution and compositions. The
positive and negative charge defects may distribute away from each
other, and their ratio may not be 1:1, because the perovskite film
surface does not necessarily reach thermal dynamic stable states
right after annealing processing, and the surfaces defects may pair
up with bulk defects. In this context, the QAH molecule with
separated positive and negative ions have the advantage of
self-adaptive selection of defects with opposite charges for
passivation, which is not limited by the complicated surface defect
composition or distribution.
[0051] To further analyze the passivation effect of the QAH,
measurements of the trap density of states (tDOS) were made for the
devices fabricated by two-step processed MAPbI.sub.3 perovskite
with choline chloride or PCBM passivation. The trap densities were
extracted using thermal admittance spectroscopy (TAS) analysis,
which is a well-established and effective technique to characterize
both shallow and deep defects of thin film and organic solar cells.
FIG. 3 shows that the device with choline chloride layers had
overall the lowest tDOS over the whole trap depth region. The
device with choline chloride layer had low tDOS in deeper trap
region (0.40-0.52 eV) which were assigned to defects at the film
surface. In addition, the density of shallower trap states
(0.35-0.40 eV), which was assigned to traps at grain boundaries, in
the choline chloride passivated devices was about three times
smaller than in the PCBM passivated devices. This indicates that
choline chloride may also diffuse into grain boundaries to
passivate them. The better passivation effect of choline chloride
than PCBM verifies that both cationic and anionic defects in OIHPs
need to be considered in passivation techniques.
[0052] The stability of OIHPs devices in the ambient condition is
challenged by their sensitivity to moisture and oxygen due to the
hydroscopic nature of the OIHP films. Recent studies revealed that
the degradation of perovskite films was generally initialized at
the defects sites at the film surface and grain boundaries where
the molecules have highest activity and diffusivity. The
passivation may also enhance the stability of the perovskite films
in ambient environment, because the healing of the defective sites
on the film surface may inhibit the permeation of moisture and
oxygen through the defects. To verify this, the stability of OIHPs
devices with choline chloride and L-.alpha.-Phosphatidylcholine
functional layers were monitored by placing the unencapsulated
devices in ambient atmosphere at room temperature and relative
humidity of 50%-85%; the device performance is summarized in FIGS.
5A-5D. The devices with choline chloride layers retained almost
100% of the initial PCEs after storage in the ambient condition for
over one month. Interestingly, the V.sub.OC of the devices
increased during the first 5 days of storage in both types of
devices with choline chloride passivation. This phenomenon may be
caused by the additional passivation effect at the anode side by
the diffusion of sodium ions into the perovskite films. The
L-.alpha.-Phosphatidylcholine modified devices showed inferior
performance, 30% loss of the initial PCE after 800 h storage in the
ambient condition, despite that the long hydrophobic alkane tails
could hinder the permeation of moisture. The difference in
stability of the devices with two passivation layers highlighted
the importance of healing both types of defects. The humidity
stability test for the bare OIHP films (FIG. 5e) shows that the
films with QAHs have much slower degradation rate than the control
films without QAHs when they were exposed to the humidity of
90.+-.5% for same time intervals. This result confirmed that the
healing of the defect sites by choline chloride effectively
improves the moisture stability of OIHPs films.
[0053] Based on the passivation mechanism, there are at least two
kinds of molecules that have the desired passivation effect. A
first kind of molecule includes molecules that have a functional
group (ammonium (--NH.sub.2), halides, small atomic radius metal
ions) which have the similar size to the corresponding vacancy, and
thereafter fill these vacancies. The following molecules are
expected to have the passivation effect because of this mechanism:
Guanidine thiocyanate, aniline, benzylamine, and phenethylamine,
Poly(ethylene glycol) bis(amine), (2-Methylbutyl)amine,
4-Pentyn-1-amine, N-Isopropylpyridin-2-amine, isochroman-6-amine,
2-phenylbutan-1-amine, 1-benzofuran-5-amine,
2-methylcyclopropan-1-amine, 3-Buten-1-amine,
1,4-Benzodioxan-6-amine, 5-methylpyrimidin-2-amine,
1-Methyl-1H-pyrazol-4-amine, 2,4,6-Trifluorobenzyl amine,
1,6-naphthyridin-2-amine, 1,2-benzisoxazol-3-amine,
1-Cyclohexyl-1H-pyrazol-5-amine, Methylammonium iodide,
Methylammonium bromide, Methylammonium chloride,
phenylethylammonium Iodide, phenylethylammonium bromide,
phenylethylammonium chloride, n-butylammonium Iodide,
n-butylammonium bromide, n-butylammonium chloride, NaCl, KCl, Ki,
NaI, CsCl, CsI, RbCl, RbI, CoI.sub.2, CoCl.sub.2, SrCl.sub.2,
SrI.sub.2. A second kind of molecule includes molecules that have
the Zwitterionic structure which is composed of positive and
negative charged components that could self-assemble with different
charged defects, resulting in the healing of the charged defects.
The following molecules are expected to have the passivation effect
because of the above mechanism: Choline chloride, Choline iodide,
Choline bromide, L-.alpha.-Phosphatidylcholine, Betaine,
Tetrabutylammonium iodide, 1-Ethyl-3-methylimidazolium iodide,
Tetrabutylammonium phosphate monobasic,
3-(4-tert-Butyl-1-pyridinio)-1-propanesulfonate,
3-(1-Pyridinio)-1-propanesulfonate,
3-(Benzyldimethylammonio)propanesulfonate,
3-(Decyldimethylammonio)-propane-sulfonate inner salt, Guanidinium
iodide, Guanidinium thiocyanate, Guanidinium chloride. The
functional molecules having at least one feature of the suitable
size or Zwitterionic structure have the passivation effect on the
OIHPs devices.
Defect Passivation Using Zwitterionic Amino Acids
[0054] Amino acids are known to have two forms, namely, regular
form and zwitterion form (see FIG. 6A on the right). In the regular
form, the N atom in the --NH.sub.2 functional group has a lone pair
of electrons which can passivate positive charged metal cations.
Meanwhile, the oxygen site in carboxyl group (--COOH) can passivate
the positively charged defects. While in the zwitterion form, amino
acids have a positive charged --NH.sub.3 end and a negative charged
--COO end, thereby may passivate both positive and negative charged
defects
[0055] In certain embodiments, zwitterionic amino acids are used
for passivating ionic defects in perovskite materials, including
hybrid perovskite materials, at both surface and grain boundaries.
Specific examples of zwitterionic amino acids include valine (VA)
and phenylalanine (PA), which both are representative of amino
acids with a hydrophobic side chain (see, FIG. 6E). For example,
DFT calculations show that valine and phenylalanine are able to
passivate both positively and negatively charged defects.
Experiments have confirmed that the charge trap density in a
valine- or phenylalanine-passivated device is reduced, e.g. as
compared to a PCBM passivated device, that an improved
open-circuit-voltage results, and that efficiency is enhanced up to
21.2%.
[0056] In certain embodiments, non-zwitterion amino acids (e.g.,
having unionized structure) may be used to passivate defects in
perovskite materials.
[0057] Advantages of amino acids include their ability to behave as
either electron donor or acceptor, as the amino acid has both
electron rich and electron deficient ends in its zwitterionic form
(as shown in FIG. 6A), thus allowing them to passivate both
positive charged and negative charged defects. Further, the sizes
of amino acids are relatively small, therefore enabling efficient
penetration into the grain boundaries to passivate the defects.
Moreover, with a proper choice of the side chain, amino acids can
be hydrophobic, thus enabling enhancement of moisture resistance.
Valine (VA) and phenylalanine (PA), two typical hydrophobic amino
acids, are discussed herein. Theoretical results predicted that
these molecules could effectively passivate both negatively charged
iodide and positively charged lead ions, which is further confirmed
from the experiment, showing that amino acids passivation
remarkably reduced the trap density and enhanced the V.sub.OC,
consequently, the PCE of valine and phenylalanine passivated
devices were boosted to 20.6% and 21.2%, respectively. These
results highlight the importance of dual passivation of the surface
and grain boundary defects to improve the efficiency of OIHP
devices.
Valine and Phenylalanine Passivation
[0058] To simulate the surface defects, a 9-layer
PbI.sub.2-terminated slab model of the tetragonal structure of
MAPbI.sub.3 as shown in FIG. 6B is used. The MAPbI.sub.3 in this
example was synthesized under the condition of slightly excess of
PbI.sub.2. Six intrinsic point defects at the surface were
considered, including two vacancies (V.sub.1, V.sub.Pb), two
interstitials (Pb.sub.i, I.sub.i) and two antisites (Pb.sub.i,
I.sub.Pb). The calculated transition levels ( (q'/q)) of donor-like
and acceptor-like defects are plotted in FIG. 6C and FIG. 6D.
V.sub.I is a shallow donor with a (0/+1) lies 0.04 eV below
conduction band minimum (CBM), while V.sub.Pb has a (0/-1)
transition level at 0.09 eV above valance band maximum (VBM) and a
(-1/-2) transition level at 0.62 eV above VBM, acting as deep
acceptors. I and Pb interstitials, and Pb.sub.2 interstitials are
shown in FIGS. 6E-6H; I interstitial is a typical negative charged
defect, while the other two are representative positive charged
defects. For two interstitials, Pb.sub.i exhibits deep transition
levels in the band gap, including (0/+1)=1.09 eV, and (+1/+2)=1.52
eV, thus acting as deep donors, while L has a (0/-1) transition
level at 0.35 eV above VBM, makes it a deep acceptor defect. For
the antisite IPb, it has (-1/-2) and (-2/-3) transition levels
above CBM, but the (0/-1) transition level lies at 0.48 eV above
VBM, making it a deep acceptor. Pb.sub.I is deep donor, with (0/1+)
and (1+/3+) transition levels at 0.29 eV and 0.43 eV below CBM. As
compared to the transition levels of intrinsic point defects in
bulk MAPbI.sub.3 (see, Yin W-J, Shi T, Yan Y. Unusual defect
physics in CH3NH3PbI3 perovskite solar cell absorber. Applied
Physics Letters 104, 063903 (2014)), the transition levels of
points defects at the surface shows a quite different picture, for
example, both I.sub.i and Pb.sub.i are benign in bulk but have deep
transition levels on the surface. This could be accounted from the
missing of space confinement effect as well as the different
bonding nature of defect sites with its neighbors on the surface as
compared to its bulk counterpart.
[0059] Although I.sub.i, V.sub.Pb, Pb.sub.i, Pb.sub.I, I.sub.Pb all
have deep transition levels, I.sub.i and Pb.sub.i defects were used
for the amino acid passivation, for the reason that under the
condition of slight excess of PbI.sub.2, the formation energy of
I.sub.i and Pb.sub.i defects are relatively lower than others. A
schematic passivation diagram can be found in FIG. 7A, where the
electron-rich --NH.sub.3 end is supposed to passivate the positive
charged defects, while the electron deficient --COO end is presumed
to neutralize the negative charged defects. The calculated
transition levels of I.sub.i and Pb.sub.i defects on valine and
phenylalanine passivated MAPbI.sub.3 surfaces are plotted in FIG.
7B. It can be clearly seen that upon valine or phenylalanine
passivation, both the deep acceptor and deep donor states become
shallower. For example, the (0/1-) transition level of I.sub.i are
at 0.15 eV and 0.18 eV above VBM for valine and phenylalanine
passivated models, respectively, while it is 0.35 eV in the
unpassivated model. For the Pb.sub.i defect, the (1+/2+) transition
level at 0.18 eV below CBM goes to above CBM after valine or
phenylalanine passivation, while the (0/1+) transition level goes
to 0.17 eV and 0.15 eV below CBM upon valine or phenylalanine
passivation, respectively, in comparison with 0.61 eV when the
surface is unpassivated.
[0060] For the I interstitial defect, additional calculations were
performed for the electronic properties of the aforementioned
passivated and unpassivated three defected surface models. From the
density of states (DOS) as plotted in FIG. 8, panels a), d) and g),
one can see that PbI.sub.2-terminated MAPbI.sub.3 surface with I
and Pb.sub.2 interstitial appear to have deep trap states (as
marked with arrows), the deep acceptor states (unoccupied) of I
interstitial are located at about 0.6 eV above the valence band
maximum (VBM), while the deep donor states (occupied) of Pb.sub.2
interstitial are located at about 0.7 eV below the conduction band
maximum (CBM). While for the Pb interstitial the defect donor state
is quite shallow, lies at about 0.04 eV below CBM. The charge
density of these defect states are plotted in FIG. 8, panels b), e)
and h), from which one can clearly see that these states are
relatively localized around the defects. For the valine passivated
ones, it is found that I interstitial can interact with the
--NH.sub.2 end in valine. The interstitial I defect gains electron
from valine, thus the deep acceptor state in the unpassivated
structure becomes an occupied state, and the new acceptor state in
the passivated structure becomes a rather delocalized one, as shown
in FIG. 8, panel i). Similarly, for the Pb.sub.2 interstitial
defect, one finds the Pb.sub.2 bond with the two O atoms in the
carboxyl group of valine in its zwitterion form, the valine gains
electron from the Pb.sub.2, and the localized donor state becomes
much more delocalized states after passivation, as shown in FIG. 8,
panel f). For the Pb interstitial defect, although the computed
energy level of the donor state is quite shallow, the charge
density of the state as plotted in FIG. 8, panel a) shows that it
is still a relatively localized state, although the passivation
does not significantly change the energy level, the new donor state
after valine passivation shows it is a delocalized one.
Photovoltaic Device Architecture and Performance
[0061] To confirm the predicted passivation effects of valine and
phenylalanine amino acids, experimental studies of the valine and
phenylalanine amino acid passivated perovskites were conducted. The
planar heterojunction perovskite solar cells in this specific
embodiment were built as poly
[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA)/CH3NH3PbI3/amino
acid passivation layer/fullerene
(C60)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/copper
(Cu), as shown in FIG. 9A. The low-temperature two-step
inter-diffusion of lead iodide (PbI.sub.2) and a methyl ammonium
iodide (MAI) stacking layer followed by a solvent annealing process
was used to synthesize the perovskite layer. PCBM is used in the
control device here. The current density-voltage (J-V) curves of
the devices with different passivation are shown in FIG. 9B. The
control device with PCBM layer shows a performance with a short
circuit current density (J.sub.SC) of 22.4 mA cm.sup.-2, an open
circuit voltage (V.sub.OC) of 1.06 eV, a fill factor (FF) of 78.4%,
and a PCE of 18.63%. Both valine and phenylalanine show
significantly improved performance, with a J.sub.SC of 22.41 mA
cm.sup.-2, a V.sub.OC of 1.14 eV, a FF of 80.5% and a PCE of 20.57%
for valine; and a J.sub.SC of 22.5 mA cm.sup.-2, a V.sub.OC of 1.19
eV, a FF of 79% and a PCE of 21.2% for phenylalanine. The V.sub.OC
of the perovskite devices was significantly increased with valine
and phenylalanine as passivation layers without sacrificing the
J.sub.SC and FF of the devices. FIG. 9C shows the V.sub.OC
distribution of the devices with different passivation layers. The
average V.sub.OC values are 1.06, 1.14, and 1.19V for the devices
with PCBM, valine and phenylalanine as passivation layer,
respectively. To further verify the passivation effect of valine
and phenylalanine amino acids, the trap density of states (tDOS)
was also measured for the devices with PCBM, valine or
phenylalanine passivation. The trap densities were extracted from
the thermal admittance spectroscopy analysis. As shown in FIG. 9D,
the devices with valine and phenylalanine have lower tDOS than PCBM
over the entire trap depth region, specifically, the device with
phenylalanine owns the lowest tDOS over the deeper trap region
(0.40-0.52 eV) and the shallower trap region (0.30-0.40 eV). It is
noted that the deeper trap states were assigned to the surface
defects, while the shallower trap region was assigned to the
defects at grain boundaries. In the shallower trap region, tDOS of
the valine passivated device is about one order lower than the PCBM
passivated device, while the phenylalanine passivated device is
strikingly more than two orders lower than that of PCBM, indicating
valine and phenylalanine amino acids can also efficiently diffuse
into the grain boundary regions, and passivate the defects
there.
Example Methods
[0062] First principles calculations. First-principles calculation
was carried out in the framework of density functional theory as
implemented in the VASP program. The generalized gradient
approximation in the form of Perdew-Burke-Ernzerhof (PBE) was used
for the exchange-correlation function. The ion-electron interaction
was treated with the projector-augmented wave method. Surface slabs
were modelled as PbI.sub.2-terminated slabs of the tetragonal
structure as the MAPbI.sub.3 was synthesized with slight excess
PbI.sub.2, the slab model has 9 layers of MAI and PbI.sub.2 in
total. About 30 .ANG. vacuum was added on top of the slab surface
to minimize the interaction between the adjacent slabs. An energy
cutoff of 500 eV was employed, and atomic positions were optimized
until the maximum force on each atom is less than 0.02 eV/.ANG..
Grimme's DFT-D3 correction was also adopted to describe the
long-range Van der Waals interaction. The thermodynamic transition
levels between different charge states of the defects were
calculated according to: (q'/q)=[DFE(q', E.sub.F=0)-DFE(q,
E.sub.F=0)]/(q-q'), where DFE(q, E.sub.F=0) is the formation energy
of defect at q charge state.
[0063] Device fabrication: Patterned ITO substrates were cleaned by
ultra-sonication with soap, acetone and isopropanol for 15 minutes,
respectively. The hole transport layer
poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA) with a
concentration of 2 mg.ml.sup.-1 dissolved in toluene was
spin-coated at a speed of 4,000 RPM for 35 s, followed by annealing
at 100.degree. C. for 10 min. The PTAA film was pre-wetted by
spinning 75 .mu.l dimethyl formamide (DMF) at 4,000 RPM for 15 s to
improve the wetting property of the perovskite precursor solution.
The perovskite precursor solution composed of mixed cations (lead
(Pb), cesium(Cs), formamidinium (FA) and methylammonium (MA)) and
halides (I, Br) was dissolved in mixed solvent (DMF/DMSO=4:1) with
a chemical formula of
Cs.sub.0.05FA.sub.0.81MA.sub.0.14PbI.sub.2.55Br.sub.0.45. The
amino-acid was added into perovskite precursor solution with the
concentration of 1.5 mg/mL. Then 80 .mu.l precursor solution was
spin-coated at 2000 RPM for 2 s and 4000 RPM for 25 s, and the film
was quickly washed with 130 .mu.l toluene at 20 s during the
procedure. The sample was annealed at 65.degree. C. and 100.degree.
C. each for 10 min. C.sub.60 (30 nm), BCP (8 nm) and copper layers
(140 nm) were thermally evaporated in sequential order to finish
the devices.
[0064] Characterization: J-V analysis of solar cells was performed
using a solar light simulator (Oriel 67005, 150 W Solar Simulator)
and the power of the simulated light was calibrated to 100
mW.cm.sup.-2 by a silicon (Si) diode (Hamamatsu S1133) equipped
with a Schott visible-color glass filter (KG5 color-filter). All
cells were measured using a Keithley 2400 source-meter with a scan
rate of 0.1 V.s.sup.-1. External quantum efficiency curves were
characterized with a Newport QE measurement kit by focusing a
monochromatic beam of light onto the devices. The tDOS of solar
cells were derived from the frequency-dependent capacitance (C-f)
and voltage dependent capacitance (C-V), which were obtained from
the TAS measurement performed by a LCR meter (Agilent E4980A).
[0065] The use of the terms "a" and "an" and "the" and "at least
one" and similar referents in the context of describing the
disclosed subject matter (especially in the context of the
following claims) are to be construed to cover both the singular
and the plural, unless otherwise indicated herein or clearly
contradicted by context. The use of the term "at least one"
followed by a list of one or more items (for example, "at least one
of A and B") is to be construed to mean one item selected from the
listed items (A or B) or any combination of two or more of the
listed items (A and B), unless otherwise indicated herein or
clearly contradicted by context. The terms "comprising," "having,"
"including," and "containing" are to be construed as open-ended
terms (i.e., meaning "including, but not limited to,") unless
otherwise noted. Recitation of ranges of values herein are merely
intended to serve as a shorthand method of referring individually
to each separate value falling within the range, unless otherwise
indicated herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context. The use of any and all examples, or example language
(e.g., "such as") provided herein, is intended merely to better
illuminate the disclosed subject matter and does not pose a
limitation on the scope of the invention unless otherwise claimed.
No language in the specification should be construed as indicating
any non-claimed element as essential to the practice of the
invention.
[0066] Certain embodiments are described herein. Variations of
those embodiments may become apparent to those of ordinary skill in
the art upon reading the foregoing description. The inventors
expect skilled artisans to employ such variations as appropriate,
and the inventors intend for the embodiments to be practiced
otherwise than as specifically described herein. Accordingly, this
disclosure includes all modifications and equivalents of the
subject matter recited in the claims appended hereto as permitted
by applicable law. Moreover, any combination of the above-described
elements in all possible variations thereof is encompassed by the
disclosure unless otherwise indicated herein or otherwise clearly
contradicted by context.
* * * * *