U.S. patent application number 12/724704 was filed with the patent office on 2010-07-22 for polymers with low band gaps and high charge mobility.
This patent application is currently assigned to Konarka Technologies, Inc.. Invention is credited to Russell Gaudiana, Richard Kingsborough, Xiaobo Shi, David Waller, Zhengguo Zhu.
Application Number | 20100180944 12/724704 |
Document ID | / |
Family ID | 37669399 |
Filed Date | 2010-07-22 |
United States Patent
Application |
20100180944 |
Kind Code |
A1 |
Gaudiana; Russell ; et
al. |
July 22, 2010 |
Polymers with low band gaps and high charge mobility
Abstract
Polymers with low band gaps and high charge mobility, as well as
related systems, methods and components are disclosed.
Inventors: |
Gaudiana; Russell;
(Merrimack, NH) ; Kingsborough; Richard; (North
Chelmsford, MA) ; Shi; Xiaobo; (Centennial, CO)
; Waller; David; (Lexington, MA) ; Zhu;
Zhengguo; (Chelmsford, MA) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Konarka Technologies, Inc.
Lowell
MA
|
Family ID: |
37669399 |
Appl. No.: |
12/724704 |
Filed: |
March 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11485708 |
Jul 13, 2006 |
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12724704 |
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11450521 |
Jun 9, 2006 |
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11485708 |
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11375643 |
Mar 14, 2006 |
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11450521 |
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60699123 |
Jul 14, 2005 |
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Current U.S.
Class: |
136/256 |
Current CPC
Class: |
C08G 61/124 20130101;
H01L 51/0047 20130101; H01L 51/0043 20130101; C08G 61/126 20130101;
B82Y 10/00 20130101; H01L 51/0036 20130101; Y02E 10/549 20130101;
C08G 61/123 20130101; H01L 51/4253 20130101; C08G 61/02
20130101 |
Class at
Publication: |
136/256 |
International
Class: |
H01L 31/00 20060101
H01L031/00 |
Claims
1. A photovoltaic cell, comprising: a first electrode, a second
electrode, and a photoactive material disposed between the first
and second electrodes, the photoactive material comprising an
electron donor material and an electron acceptor material, the
electron donor material comprises a copolymer including a first
monomer repeat unit, and the first monomer repeat unit comprises a
thienothiophene moiety.
2. The photovoltaic cell of claim 1, wherein the thienothiophene
moiety is optionally substituted with at least one substituent
selected from the group consisting of C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2,
and SO.sub.2R, in which R is H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl.
3. The photovoltaic cell of claim 1, wherein the thienothiophene
moiety is optionally substituted with halo.
4. The photovoltaic cell of claim 1, wherein the thienothiophene
moiety is optionally substituted with fluoro.
5. The photovoltaic cell of claim 1, wherein the electron acceptor
material comprises a fullerene.
6. The photovoltaic cell of claim 1, wherein the electron acceptor
material comprises a substituted fullerene.
7. The photovoltaic cell of claim 1, wherein the electron acceptor
material comprises a PCBM.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Utility
application Ser. No. 11/485,708, filed Jul. 13, 2006, which in turn
is a continuation-in-part of U.S. Utility application Ser. No.
11/450,521, filed Jun. 9, 2006, which in turn is a
continuation-in-part of U.S. Utility application Ser. No.
11/375,643, filed Mar. 14, 2006, which claims priority to U.S.
Provisional Application Ser. No. 60/699,123, filed Jul. 14, 2005.
The contents of all parent applications are hereby incorporated by
reference.
TECHNICAL FIELD
[0002] This disclosure generally relates to the field of electron
donor materials, as well as related photovoltaic cells.
BACKGROUND OF THE INVENTION
[0003] Photovoltaic cells are commonly used to transfer energy in
the form of light into energy in the form of electricity. A typical
photovoltaic cell includes a photoactive material disposed between
two electrodes. Generally, light passes through one or both of the
electrodes to interact with the photoactive material. As a result,
the ability of one or both of the electrodes to transmit light
(e.g., light at one or more wavelengths absorbed by a photoactive
material) can limit the overall efficiency of a photovoltaic cell.
In many photovoltaic cells, a film of semiconductive material
(e.g., indium tin oxide) is used to form the electrode(s) through
which light passes because, although the semiconductive material
can have a lower electrical conductivity than electrically
conductive materials, the semiconductive material can transmit more
light than many electrically conductive materials.
SUMMARY
[0004] An aspect of the invention relates to a new combination of
monomers that produce polymers, wherein the polymers have
properties suitable for use as charge carriers in the active layer
of a photovoltaic cell.
[0005] In one aspect, the invention features a class of co-polymers
including at least two co-monomers, at least one of which is a
cyclopentadithiophene.
[0006] In another aspect, this invention features a photovoltaic
cell including a first electrode, a second electrode, and a
photoactive material disposed between the first and second
electrodes. The photoactive material includes a polymer having a
first comonomer repeat unit and a second comonomer repeat unit. The
first comonomer repeat unit includes a cyclopentadithiophene
moiety. The second comonomer repeat unit includes a silole moiety,
a thienothiophene moiety, a thienothiophene oxide moiety, a
dithienothiophene moiety, a dithienothiophene oxide moiety, or a
tetrahydroisoindole moiety.
[0007] In another aspect, this invention features a photovoltaic
cell including a first electrode, a second electrode, and a
photoactive material disposed between the first and second
electrodes. The photoactive material includes a polymer having a
first comonomer repeat unit and a second comonomer repeat unit
different from the first comonomer repeat unit. The first comonomer
repeat unit includes a cyclopentadithiophene moiety.
[0008] In another aspect, this invention features a polymer that
includes a first comonomer repeat unit containing a
cyclopentadithiophene moiety, and a second comonomer repeat unit
containing a benzothiadiazole moiety, a thiadiazoloquinoxaline
moiety, a cyclopentadithiophene oxide moiety, a benzoisothiazole
moiety, a benzothiazole moiety, a thiophene oxide moiety, a
fluorene moiety, a thiophene moiety, a silole moiety, a
thienothiophene moiety, a thienothiophene oxide moiety, a
dithienothiophene moiety, a dithienothiophene oxide moiety, a
tetrahydroisoindole moiety, or a moiety containing at least three
thiophene moieties.
[0009] In another aspect, this invention features a polymer that
includes a first comonomer repeat unit and a second comonomer
repeat unit different from the first comonomer repeat unit. The
first comonomer repeat unit contains a cyclopentadithiophene moiety
substituted with at least one substituent selected from the group
consisting of hexyl, ethylhexyl, dimethyloctyl, C.sub.1-C.sub.20
alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl, and
C.sub.3-C.sub.20 heterocycloalkyl.
[0010] In another aspect, this invention features a device (e.g., a
photovoltaic cell) that includes a first electrode, a second
electrode, and a photoactive material disposed between the first
and second electrodes. The photoactive material includes a polymer
having a first monomer repeat unit, which includes a
benzothiadiazole moiety, a thiophene oxide moiety, a
cyclopentadithiophene oxide moiety, a thiadiazoloquinoxaline
moiety, a benzoisothiazole moiety, a benzothiazole moiety, a
thienothiophene moiety, a thienothiophene oxide moiety, a
dithienothiophene moiety, a dithienothiophene oxide moiety, a
tetrahydroisoindole moiety, a fluorene moiety, a thiophene moiety,
a silole moiety, or a fluorene moiety.
[0011] In another aspect, this invention features a device (e.g., a
photovoltaic cell) that includes a first electrode, a second
electrode, and a photoactive material disposed between the first
and second electrodes. The photoactive material includes a polymer
having a first monomer repeat unit, which includes a
cyclopentadithiophene moiety substituted with at least one
substituent selected from the group consisting of hexyl,
ethylhexyl, dimethyloctyl, C.sub.1-C.sub.20 alkoxy, aryl,
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20
heterocycloalkyl halo, CN, NO.sub.2, or SO.sub.2R, in which R is
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20
heterocycloalkyl.
[0012] Embodiments can include one or more of the following
features.
[0013] In some embodiments, the cyclopentadithiophene moiety is
substituted with at least one substituent selected from the group
consisting of C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy,
aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20
heterocycloalkyl, halo, CN, NO.sub.2, and SO.sub.2R, in which R is
H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl,
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20
heterocycloalkyl. Examples of C.sub.1-C.sub.20 alkyl can be hexyl,
2-ethylhexyl, or 3,7-dimethyloctyl.
[0014] In some embodiments, the cyclopentadithiophene moiety can be
substituted at 4-position.
[0015] In some embodiments, the first monomer or comonomer repeat
unit can include a cyclopentadithiophene moiety of formula (I):
##STR00001##
In formula (I), each of R.sub.1, R.sub.2, R.sub.3, and R.sub.4,
independently, is H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20
alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl,
C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2, or
SO.sub.2R, in which R is H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl. In some
embodiments, at least one of R.sub.1 and R.sub.2, independently, is
hexyl, 2-ethylhexyl, or 3,7-dimethyloctyl. In certain embodiments,
each of R.sub.1 and R.sub.2, independently, is hexyl, 2-ethylhexyl,
or 3,7-dimethyloctyl. In some embodiments, one of R.sub.1 and
R.sub.2 is hexyl, ethylhexyl, dimethyloctyl, C.sub.1-C.sub.20
alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl, or
C.sub.3-C.sub.20 heterocycloalkyl, the other of R.sub.1 and R.sub.2
is H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl,
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20
heterocycloalkyl. In some embodiments, at least one of R.sub.1 and
R.sub.2, independently, is C.sub.1-C.sub.20 alkoxy optionally
further substituted with C.sub.1-C.sub.20 alkoxy or halo (e.g.,
(OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3). In certain
embodiments, each of R.sub.1 and R.sub.2, independently, is
C.sub.1-C.sub.20 alkoxy optionally further substituted with
C.sub.1-C.sub.20 alkoxy or halo.
[0016] In some embodiments, the second comonomer repeat unit can
include a benzothiadiazole moiety, a thiadiazoloquinoxaline moiety,
a cyclopentadithiophene oxide moiety, a benzoisothiazole moiety, a
benzothiazole moiety, a thiophene oxide moiety, a thienothiophene
moiety, a thienothiophene oxide moiety, a dithienothiophene moiety,
a dithienothiophene oxide moiety, a tetrahydroisoindole moiety, a
fluorene moiety, a thiophene moiety, or a silole moiety, each of
which is optionally substituted with at least one substituent
selected from the group consisting of C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2,
and SO.sub.2R, in which R is H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl. In some
embodiments, the second comonomer repeat unit can include a
3,4-benzo-1,2,5-thiadiazole moiety.
[0017] In some embodiments, the second comonomer repeat unit can
include a benzothiadiazole moiety of formula (II), a
thiadiazoloquinoxaline moiety of formula (III), a
cyclopentadithiophene dioxide moiety of formula (IV), a
cyclopentadithiophene monoxide moiety of formula (V), a
benzoisothiazole moiety of formula (VI), a benzothiazole moiety of
formula (VII), a thiophene dioxide moiety of formula (VIII), a
cyclopentadithiophene dioxide moiety of formula (IX), or a
cyclopentadithiophene tetraoxide moiety of formula (X):
##STR00002## ##STR00003##
in which each of R.sub.5, R.sub.6, and R.sub.7, independently, is
H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl,
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20
heterocycloalkyl, halo, CN, NO.sub.2, and SO.sub.2R, in which R is
H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl,
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20
heterocycloalkyl. In some embodiments, the second comonomer repeat
unit can include a benzothiadiazole moiety of formula (II). In
certain embodiments, R.sub.5 and R.sub.6 is H.
[0018] In some embodiments, the second comonomer repeat unit can
include at least three thiophene moieties. In some embodiments, at
least one of the thiophene moieties is substituted with at least
one substituent selected from the group consisting of
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl,
halo, CN, NO.sub.2, and SO.sub.2R, in which R is H,
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl.
In certain embodiments, the second comonomer repeat unit includes
five thiophene moieties.
[0019] In some embodiments, the second comonomer repeat unit can
include a thienothiophene moiety of formula (XI), a thienothiophene
tetraoxide moiety of formula (XII), a dithienothiophene moiety of
formula (XIII), a dithienothiophene dioxide moiety of formula
(XIV), a dithienothiophene tetraoxide moiety of formula (XV), a
tetrahydroisoindole moiety of formula (XVI), a thienothiophene
dioxide moiety of formula (XVII), or a dithienothiophene dioxide
moiety of formula (XVIII):
##STR00004##
in which each of X and Y, independently, is CH.sub.2, O, or S; each
of R.sub.5 and R.sub.6, independently, is H, C.sub.1-C.sub.20
alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2,
or SO.sub.2R, in which R is C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl; and R.sub.7 is H,
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20
heterocycloalkyl.
[0020] In some embodiments, the polymer can further include a third
comonomer repeat unit that contains a thiophene moiety or a
fluorene moiety. In some embodiments, the thiophene or fluorene
moiety is substituted with at least one substituent selected from
the group consisting of C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20
alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl, and
C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2, and
SO.sub.2R, in which R is H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl.
[0021] In some embodiments, the first monomer or comonomer repeat
unit can include a benzothiadiazole moiety of formula (II), a
thiophene dioxide moiety of formula (VIII), a cyclopentadithiophene
tetraoxide moiety of formula (X), or a fluorene moiety of formula
(XIX):
##STR00005##
in which each of R.sub.5 and R.sub.6, independently, is H,
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl,
halo, CN, NO.sub.2, or SO.sub.2R. R can be C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl. In some
embodiments, at least one of R.sub.5 and R.sub.6 can be
C.sub.1-C.sub.20 alkoxy optionally further substituted with
C.sub.1-C.sub.20 alkoxy or halo (e.g.,
(OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3).
[0022] In some embodiments, the polymer can include a second
monomer repeat unit different from the first monomer repeat unit.
The second monomer repeat unit can include a cyclopentadithiophene
moiety, a benzothiadiazole moiety, a thiophene oxide moiety, a
cyclopentadithiophene oxide moiety, a fluorene moiety, or a
thiophene moiety.
[0023] In some embodiments, the first or second monomer repeat unit
can include at least one substituent on a ring selected from the
group consisting of C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20
alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20 cycloalkyl,
C.sub.3-C.sub.20 heterocycloalkyl, halo, CN, NO.sub.2, and
SO.sub.2R, in which R is H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl. The substituent
can be hexyl, ethylhexyl, or C.sub.1-C.sub.20 alkoxy optionally
further substituted with C.sub.1-C.sub.20 alkoxy or halo (e.g.,
(OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3).
[0024] In some embodiments, the second monomer repeat unit can
include a cyclopentadithiophene moiety of formula (I), a
benzothiadiazole moiety of formula (II), a thiophene dioxide moiety
of formula (VIII), a cyclopentadithiophene tetraoxide moiety of
formula (X), a fluorene moiety of formula (XIX), a thiophene moiety
of formula (XX), or a silole moiety of formula (XXI):
##STR00006##
in which each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5,
R.sub.6, R.sub.7, and R.sub.8, independently, is H,
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20 heterocycloalkyl,
halo, CN, NO.sub.2, or SO.sub.2R. R can be C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl. In some
embodiments, at least one of R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, R.sub.6, R.sub.7, and R.sub.8, can be C.sub.1-C.sub.20
alkoxy optionally further substituted with C.sub.1-C.sub.20 alkoxy
or halo (e.g., (OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3).
[0025] In some embodiments, when the second comonomer contains a
silole moiety of formula (XXI), at least one of R.sub.5, R.sub.6,
R.sub.7 and R.sub.8 can be C.sub.1-C.sub.20 alkyl optionally
substituted with halo, or aryl optionally substituted with
C.sub.1-C.sub.20 alkyl. In certain embodiments, each of R.sub.5 and
R.sub.6, independently can be aryl optionally substituted with
C.sub.1-C.sub.20 alkyl, and each of R.sub.7 and R.sub.8,
independently, can be C.sub.1-C.sub.20 alkyl optionally substituted
with halo. An example of a silole moiety is
##STR00007##
[0026] In some embodiments, the polymer can be an electron donor
material or an electron acceptor material.
[0027] In some embodiments, the polymer can be
##STR00008##
in which n can be an integer greater than 1.
[0028] In some embodiments, the photovoltaic cell can be a tandem
photovoltaic cell.
[0029] In some embodiments, the photoactive material can include an
electron acceptor material. In some embodiments, the electron
acceptor material can be a fullerene (e.g., C61-phenyl-butyric acid
methyl ester, PCBM).
[0030] In some embodiments, the polymer and the electron acceptor
material each can have a LUMO energy level. The LUMO energy level
of the polymer can be at least about 0.2 eV (e.g., at least about
0.3 eV) less negative than the LUMO energy level of the electron
acceptor material.
[0031] In some embodiments, the device can be an organic
semiconductive device. In certain embodiments, the device can be a
member selected from the group consisting of field effect
transistors, photodetectors, photovoltaic detectors, imaging
devices, light emitting diodes, lasing devices, conversion layers,
amplifiers and emitters, storage elements, and electrochromic
devices.
[0032] Embodiments can provide one or more of the following
advantages.
[0033] In some embodiments, using a polymer containing a
cyclopentadithiophene moiety can be advantageous because the
cyclopentadithiophene moiety can contribute to a shift in the
maximum absorption wavelength toward the red or near IR region of
the electromagnetic spectrum. When such a polymer is incorporated
into a photovoltaic cell, the current and efficiency of the cell
can increase.
[0034] In some embodiments, substituted fullerenes or polymers
containing substituted monomer repeat units (e.g., substituted with
long-chain alkoxy groups such as oligomeric ethylene oxides or
fluorinated alkoxy groups) can have improved solubility in organic
solvents and can form an photoactive layer with improved
morphology.
[0035] In some embodiments, a polymer containing a silole moiety
can absorb light at a relatively long wavelength and have improved
solubility in organic solvents. In some embodiments, a polymer
containing a silole moiety can be used to prepare an electron donor
material with improved semiconductive properties.
[0036] In some embodiments, a polymer fullerene cell containing a
polymer described above can have a band gap that is relatively
ideal for its intended purposes.
[0037] In some embodiments, a photovoltaic cell having high cell
voltage can be created, whereby the HOMO level of the polymer is at
least about 0.2 electron volts more negative relative to the LUMO
or conduction band of an electron acceptor material.
[0038] In some embodiments, a photovoltaic cell containing a
polymer described above can have relatively fast and efficient
transfer of an electron to an electron acceptor material, whereby
the LUMO of the donor is at least about 0.2 electron volt (e.g., at
least about 0.3 electron volt) less negative than the conduction
band of the electron acceptor material.
[0039] In some embodiments, a photovoltaic cell containing a
polymer described above can have relatively fast charge separation,
whereby the charge mobility of the positive charge, or hole, is
relatively high and falls within the range of 10.sup.-4 to
10.sup.-1 cm.sup.2/Vs.
[0040] In some embodiments, the polymer is soluble in an organic
solvent and/or film forming.
[0041] In some embodiments, the polymer is optically
non-scattering.
[0042] In some embodiments, the polymer can be used in organic
field effect transistors and OLEDs.
[0043] Other features and advantages of the invention will be
apparent from the description, drawings, and claims.
DESCRIPTION OF DRAWING
[0044] FIG. 1 is a cross-sectional view of an embodiment of a
photovoltaic cell.
[0045] FIG. 2 is a schematic of a system containing one electrode
between two photoactive layers.
[0046] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0047] FIG. 1 shows a cross-sectional view of a photovoltaic cell
100 that includes a substrate 110, a cathode 120, a hole carrier
layer 130, an active layer 140 (containing an electron acceptor
material and an electron donor material), a hole blocking layer
150, an anode 160, and a substrate 170.
[0048] In general, during use, light impinges on the surface of
substrate 110, and passes through substrate 110, cathode 120, and
hole carrier layer 130. The light then interacts with active layer
140, causing electrons to be transferred from the electron donor
material (e.g., a polymer described above) to the electron acceptor
material (e.g., PCBM). The electron acceptor material then
transmits the electrons through hole blocking layer 150 to anode
160, and the electron donor material transfers holes through hole
carrier layer 130 to cathode 120. Anode 160 and cathode 120 are in
electrical connection via an external load so that electrons pass
from anode 160, through the load, and to cathode 120.
[0049] Electron acceptor materials of active layer 140 can include
fullerenes. In some embodiments, active layer 140 can include one
or more unsubstituted fullerenes and/or one or more substituted
fullerenes. Examples of unsubstituted fullerenes include C.sub.60,
C.sub.70, C.sub.76, C.sub.78, C.sub.82, C.sub.84, and C.sub.92.
Examples of substituted fullerenes include PCBM or fullerenes
substituted with C.sub.1-C.sub.20 alkoxy optionally further
substituted with C.sub.1-C.sub.20 alkoxy or halo (e.g.,
(OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3). Without wishing to be
bound by theory, it is believed that fullerenes substituted with
long-chain alkoxy groups (e.g., oligomeric ethylene oxides) or
fluorinated alkoxy groups have improved solubility in organic
solvents and can form an photoactive layer with improved
morphology.
[0050] In some embodiments, the electron acceptor materials can
include polymers (e.g., homopolymers or copolymers). A polymers
mentioned herein include at least two identical or different
monomer repeat units (e.g., at least 5 monomer repeat units, at
least 10 monomer repeat units, at least 50 monomer repeat units, at
least 100 monomer repeat units, or at least 500 monomer repeat
units). A copolymer mentioned herein refers to a polymer that
includes at least two co-monomers of differing structures. In some
embodiments, the polymers used as an electron acceptor material can
include one or more monomer repeat units listed in Tables 1 and 2
below. Specifically, Table 1 lists examples of the monomers that
can be used as an electron donating monomer and can serve as a
conjugative link. Table 2 lists examples of the monomers that can
be used as an electron withdrawing monomer. Note that depending on
the substituents, monomers listed in Table 1 can also be used as
electron withdrawing monomers and monomers listed in Table 2 can
also be used as electron donating monomers. Preferably, the
polymers used as an electron acceptor material include a high molar
percentage (e.g., at least about 50%, at least about 60%, at least
about 70%, at least about 80%, at least about 90%) of an electron
withdrawing monomer.
[0051] Electron donor materials of active layer 140 can include
polymers (e.g., homopolymers or copolymers). In some embodiments,
the polymers used as an electron donor material can include one or
more monomer repeat units listed Tables 1 and 2. Preferably, the
polymers used as an electron donor material include a high molar
percentage (e.g., at least about 50%, at least about 60%, at least
about 70%, at least about 80%, at least about 90%) of an electron
donating monomer. In some embodiments, the polymers include a
monomer containing C.sub.1-C.sub.20 alkoxy on a ring, which is
optionally further substituted with C.sub.1-C.sub.20 alkoxy or halo
(e.g., (OCH.sub.2CH.sub.2).sub.2OCH.sub.3 or
OCH.sub.2CF.sub.2OCF.sub.2CF.sub.2OCF.sub.3). Without wishing to be
bound by theory, it is believed that polymers containing monomers
substituted with long-chain alkoxy groups (e.g., oligomeric
ethylene oxides) or fluorinated alkoxy groups have improved
solubility in organic solvents and can form an photoactive layer
with improved morphology.
TABLE-US-00001 TABLE 1 ##STR00009## ##STR00010## ##STR00011##
TABLE-US-00002 TABLE 2 ##STR00012## ##STR00013## ##STR00014##
##STR00015## ##STR00016## ##STR00017## ##STR00018## ##STR00019##
##STR00020## ##STR00021## ##STR00022## ##STR00023## ##STR00024##
##STR00025## ##STR00026## ##STR00027## ##STR00028##
##STR00029##
[0052] Referring to formulas listed in Tables 1 and 2 above, each
of X and Y, independently, can be CH.sub.2, O, or S; each of
R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and
R.sub.8, independently, can be H, C.sub.1-C.sub.20 alkyl,
C.sub.1-C.sub.20 alkoxy, aryl (e.g., phenyl or substituted phenyl),
heteroaryl, C.sub.3-C.sub.20 cycloalkyl, C.sub.3-C.sub.20
heterocycloalkyl, halo, CN, NO.sub.2, or SO.sub.2R; and R.sub.7 can
be H, C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl (e.g.,
phenyl or substituted phenyl), heteroaryl, C.sub.3-C.sub.20
cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl; in which R is
C.sub.1-C.sub.20 alkyl, C.sub.1-C.sub.20 alkoxy, aryl, heteroaryl,
C.sub.3-C.sub.20 cycloalkyl, or C.sub.3-C.sub.20 heterocycloalkyl.
An alkyl can be saturated or unsaturated and branch or straight
chained. A C.sub.1-C.sub.20 alkyl contains 1 to 20 carbon atoms
(e.g., one, two, three, four, five, six, seven, eight, nine, 10,
11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples
of alkyl moieties include --CH.sub.3, --CH.sub.2--,
--CH.sub.2.dbd.CH.sub.2--, --CH.sub.2--CH.dbd.CH.sub.2, and
branched --C.sub.3H.sub.7. An alkoxy can be branch or straight
chained and saturated or unsaturated. An C.sub.1-C.sub.20 alkoxy
contains an oxygen radical and 1 to 20 carbon atoms (e.g., one,
two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples of alkoxy
moieties include --OCH.sub.3 and --OCH.dbd.C.sub.2H.sub.4. A
cycloalkyl can be either saturated or unsaturated. A
C.sub.3-C.sub.20 cycloalkyl contains 3 to 20 carbon atoms (e.g.,
three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15,
16, 17, 18, 19, and 20 carbon atoms). Examples of cycloalkyl
moieties include cyclohexyl and cyclohexen-3-yl. A heterocycloalkyl
can also be either saturated or unsaturated. A C.sub.3-C.sub.20
heterocycloalkyl contains at least one ring heteroatom (e.g., O, N,
and S) and 3 to 20 carbon atoms (e.g., three, four, five, six,
seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20
carbon atoms). Examples of heterocycloalkyl moieties include
4-tetrahydropyranyl and 4-pyranyl. An aryl can contain one or more
aromatic rings. Examples of aryl moieties include phenyl,
phenylene, naphthyl, naphthylene, pyrenyl, anthryl, and
phenanthryl. A heteroaryl can contain one or more aromatic rings,
at least one of which contains at least one ring heteroatom (e.g.,
O, N, and S). Examples of heteroaryl moieties include furyl,
furylene, fluorenyl, pyrrolyl, thienyl, oxazolyl, imidazolyl,
thiazolyl, pyridyl, pyrimidinyl, quinazolinyl, quinolyl,
isoquinolyl, and indolyl.
[0053] Alkyl, alkoxy, cycloalkyl, heterocycloalkyl, aryl, and
heteroaryl mentioned herein include both substituted and
unsubstituted moieties, unless specified otherwise. Examples of
substituents on cycloalkyl, heterocycloalkyl, aryl, and heteroaryl
include C.sub.1-C.sub.20 alkyl, C.sub.3-C.sub.20 cycloalkyl,
C.sub.1-C.sub.20 alkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy,
amino, C.sub.1-C.sub.10 alkylamino, C.sub.1-C.sub.20 dialkylamino,
arylamino, diarylamino, hydroxyl, halogen, thio, C.sub.1-C.sub.10
alkylthio, arylthio, C.sub.1-C.sub.10 alkylsulfonyl, arylsulfonyl,
cyano, nitro, acyl, acyloxy, carboxyl, and carboxylic ester.
Examples of substituents on alkyl include all of the above-recited
substituents except C.sub.1-C.sub.20 alkyl. Cycloalkyl,
heterocycloalkyl, aryl, and heteroaryl also include fused
groups.
[0054] The copolymers described above can be prepared by methods
known in the art. For example, a copolymer can be prepared by a
cross-coupling reaction between one or more comonomers containing
two alkylstannyl groups and one or more comonomers containing two
halo groups in the presence of a transition metal catalyst. As
another example, a copolymer can be prepared by a cross-coupling
reaction between one or more comonomers containing two borate
groups and one or more comonomers containing two halo groups in the
presence of a transition metal catalyst. The comonomers can be
prepared by the methods described herein or by the methods know in
the art, such as those described in Coppo et al., Macromolecules
2003, 36, 2705-2711 and Kurt et al., J. Heterocycl. Chem. 1970, 6,
629, the contents of which are hereby incorporated by
reference.
[0055] Table 3 below lists three exemplary polymers (i.e., polymers
1-3) described in the Summary section above. These polymers can
have unique properties, which make them particularly suitable as
charge carriers in the active layer of a photovoltaic cell.
Polymers 1 and 2 can be obtained by the methods described in
Examples 4 and 7 below.
TABLE-US-00003 TABLE 3 ##STR00030## ##STR00031## ##STR00032##
[0056] Generally, one co-monomer in the polymers described in the
Summary section above is a cyclopentadithiophene. An advantage of a
co-polymer containing a cyclopentadithiophene moiety is that its
absorption wavelength can shift toward the red and near IR portion
(e.g., 650-800 nm) of the electromagnetic spectrum, which is not
accessible by most other polymers. When such a co-polymer is
incorporated into a photovoltaic cell, it enables the cell to
absorb the light in this region of the spectrum, thereby increasing
the current and efficiency of the cell.
[0057] The polymers described above can be useful in solar power
technology because the band gap is close to ideal for a
photovoltaic cell (e.g., a polymer-fullerene cell). The HOMO level
of the polymers can be positioned correctly relative to the LUMO of
an electron acceptor (e.g., PCBM) in a photovoltaic cell (e.g., a
polymer-fullerene cell), allowing for high cell voltage. The LUMO
of the polymers can be positioned correctly relative to the
conduction band of the electron acceptor in a photovoltaic cell,
thereby creating efficient transfer of an electron to the electron
acceptor. For example, using a polymer having a band gap of about
1.4-1.6 eV can significantly enhance cell voltage. Cell
performance, specifically efficiency, cam benefit from both an
increase in photocurrent and an increase in cell voltage, and can
approach and even exceed 15% efficiency. The positive charge
mobility of the polymers can be relatively high and approximately
in the range of 10.sup.-4 to 10.sup.-1 cm.sup.-2/Vs. In general,
the relatively high positive charge mobility allows for relatively
fast charge separation. The polymers can also be soluble in an
organic solvent and/or film forming. Further, the polymers can be
optically non-scattering.
[0058] Components in photovoltaic cell other than the electro
acceptor materials and the electron donor materials are known in
the art, such as those described in U.S. patent application Ser.
No. 10/723,554, the contents of which are incorporated herein by
references.
[0059] In some embodiments, the polymer described above can be used
as an electron donor material or an electro acceptor material in a
system in which two photovoltaic cells share a common electrode.
Such a system is also known as tandem photovoltaic cell. Examples
of tandem photovoltaic cells are discussed in U.S. patent
application Ser. No. 10/558,878, filed Nov. 29, 2005, the contents
of which are hereby incorporated by reference.
[0060] As an example, FIG. 2 is a schematic of a tandem
photovoltaic cell 200 having a substrate 210, three electrodes 220,
240, and 260, and two photoactive layers 230 and 250. Electrode 240
is shared between photoactive layers 230 and 250, and is
electrically connected with electrodes 220 and 260. In general,
electrodes 220, 240, and 260 can be formed of an electrically
conductive material, such as those described in U.S. patent
application Ser. No. 10/723,554. In some embodiments, one or more
(i.e., one, two, or three) electrodes 220, 240, and 260 is a mesh
electrode. In some embodiments, one or more electrodes 220, 240,
and 260 is formed of a semiconductive material. Examples of
semiconductive materials include titanium oxides, indium tin
oxides, fluorinated tin oxides, tin oxides, and zinc oxides. In
certain embodiments, one or more (i.e., one, two, or three)
electrodes 220, 240, and 260 are formed of titanium dioxide.
Titanium dioxide used to prepare an electrode can be in any
suitable forms. For example, titanium dioxide can be in the form of
interconnected nanoparticles. Examples of interconnected titanium
dioxide nanoparticles are described, for example, in U.S. Pat. No.
7,022,910, the contents of which are incorporated herein by
reference. In some embodiments, at least one (e.g., one, two, or
three) of electrodes 220, 240, and 260 is a transparent electrode.
As referred to herein, a transparent electrode is formed of a
material which, at the thickness used in a photovoltaic cell,
transmits at least about 60% (e.g., at least about 70%, at least
about 75%, at least about 80%, at least about 85%, at least about
90%, at least about 95%) of incident light at a wavelength or a
range of wavelengths used during operation of the photovoltaic
cell. In certain embodiments, both electrodes 220 and 260 are
transparent electrodes.
[0061] Each of photoactive layers 230 and 250 can contain at least
one semiconductive material. In some embodiments, the
semiconductive material in photoactive layer 230 has the same band
gap as the semiconductive material in photoactive layer 250. In
certain embodiments, the semiconductive material in photoactive
layer 230 has a band gap different from that of the semiconductive
material in photoactive layer 250. Without wishing to be bound by
theory, it is believed that incident light not absorbed by one
photoactive layer can be absorbed by the other photoactive layer,
thereby maximizing the absorption of the incident light.
[0062] In some embodiments, at least one of photoactive layers 230
and 250 can contain an electron acceptor material (e.g., PCBM or a
polymer described above) and an electron donor material (e.g., a
polymer described above). In general, suitable electron acceptor
materials and electron donor materials can be those described
above. In certain embodiments, each of photoactive layers 230 and
250 contains an electron acceptor material and an electron donor
material.
[0063] Substrate 210 can be formed of one or more suitable
polymers, such as those described in U.S. patent application Ser.
No. 10/723,554. In some embodiments, an additional substrate (not
shown in FIG. 2) can be disposed on electrode 260.
[0064] Photovoltaic cell 200 can further contain a hole carrier
layer (not shown in FIG. 2) and a hole blocking layer (not shown in
FIG. 2), such as those described in U.S. patent application Ser.
No. 10/723,554.
[0065] While photovoltaic cells have been described above, in some
embodiments, the polymers described herein can be used in other
devices and systems. For example, the polymers can be used in
suitable organic semiconductive devices, such as field effect
transistors, photodetectors (e.g., IR detectors), photovoltaic
detectors, imaging devices (e.g., RGB imaging devices for cameras
or medical imaging systems), light emitting diodes (LEDs) (e.g.,
organic LEDs or IR or near IR LEDs), lasing devices, conversion
layers (e.g., layers that convert visible emission into IR
emission), amplifiers and emitters for telecommunication (e.g.,
dopants for fibers), storage elements (e.g., holographic storage
elements), and electrochromic devices (e.g., electrochromic
displays).
[0066] The following examples are illustrative and not intended to
be limiting.
Example 1
Synthesis of 4,4-Dihexyl-4H-cyclopenta[2,1-b;3,4-b']dithiophene
##STR00033##
[0068] 4H-Cyclopenta[2,1-b;3,4-b']dithiophene was synthesized
according to literature procedure illustrated in Coppo et al.,
Macromolecules 2003, 36, 2705-2711. All other starting materials
were purchased from Sigma-Aldrich and used as received.
[0069] 4H-Cyclopenta[2,1-b;3,4-b']dithiophene (1.5 g, 0.00843 mol)
was dissolved in DMSO (50 mL). The solution was purged with
nitrogen, and grounded KOH (1.89 g, 0.0337 mol) and sodium iodide
(50 mg) were added, followed by hexyl bromide (3.02 g, 0.0169 mol).
The reaction was stirred for 17 h under nitrogen at room
temperature. Water was added and the reaction was extracted with
t-butyl-methyl ether. The organic layer was separated and dried
over magnesium sulfate. Solvent was removed under vacuum and the
residue was purified by chromatography using hexanes as eluent.
Fractions containing pure
4,4-dixeyl-4H-cyclopenta[2,1-b;3,4-b]dithiophene product were
combined and the solvents evaporated. The product was obtained as a
colorless oil. Yield: 2.36 g (81%).
Example 2
The Synthesis of
4,4-Dihexyl-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-b;3,4-b']dithiop-
hene
##STR00034##
[0071] Starting material
4,4-dihexyl-4H-cyclopenta[2,1-b;3,4-b]dithiophene (1.5 g, 0.00433
mol) was dissolved in dry THF (30 mL). The solution was cooled to
-78.degree. C. and butyl lithium (6.1 mL, 0.0130 mol) was added
drop wise. The reaction was stirred at this temperature for 2 h and
warmed to room temperature, stirred for 3 h. Again reaction was
cooled to -78.degree. C. and trimethyltin chloride (1 M in hexanes,
16.0 mL, 16.0 mmol) was added dropwise. The reaction was allowed to
warm to rt and stirred for 17 h. Water was added and the reaction
was extracted with toluene. The organic layer was washed with water
and dried over sodium sulfate. Solvent was removed under vacuum and
the residue was dissolved in toluene, and quickly passed through a
plug of silica gel pretreated with triethyl amine. Solvent was
removed and the residue dried under vacuum to afford 2.65 g of the
bis(trimethyltin) monomer. .sup.1H NMR (CDCl.sub.3, 200 MHz): 6.97
(m, 2H), 1.84 (m, 4H), 1.20 (m, 16H), 0.88 (m, 6H), 0.42 (m,
18H).
Example 3
The Synthesis of
bis-(tributylstannyl)-4,4-dihexyl-cyclopenta[2,1-b:3,4-b']dithiophene
##STR00035##
[0073] 4,4-Dihexyl-4H-cyclopenta[2,1-b;3,4-b]dithiophene (2.2 g,
0.0065 mol) was dissolved in dry THF (20 mL). The solution was
cooled to -78.degree. C. BuLi (7.62, 2.5 M in hexanes, 0.019 mol)
was then added to the solution. The reaction mixture was allowed to
warm to room temperature and was stirred for 5 hours. The mixture
was then cooled again to -78.degree. C. and Bu.sub.3SnCl (7.44 g,
0.0229 mol) was added. The reaction mixture was allowed to warm to
room temperature and was stirred for another 48 hours. Water was
then added and the mixture was extracted with dihicholomethane.
Organic layer was collected, dried over anhydrous Na.sub.2SO.sub.4,
and concentrated. The residue thus obtained was dissolved in hexane
and quickly passed through a plug of silica gel pretreated with
triethylamine. The solvent was removed and the residue was dried
under vacuum to afford
bis-(tributylstannyl)-4,4-dihexyl-cyclopenta[2,1-b:3,4-b']dithiophene
(5.7 g).
Example 4
Polymerization of
bis-(tributylstannyl)-4,4-dihexyl-cyclopenta[2,1-b:3,4-b']dithiophene
and 4,7-dibromo-2,1,3-benzothiadiazole
##STR00036##
[0075]
Bis-(tributylstannyl)-4,4-dihexyl-cyclopenta[2,1-b:3,4-b']dithiophe-
ne (0.775 g, 0.000816 mol) and 4,7-dibromo-2,1,3-benzothiadiazole
(0.24 g, 0.000816 mol) were first dissolved in toluene. After the
reaction was purged with nitrogen, palladium
tretakistriphenylphosphine (15 mg, 0.0065 mmol) was added. The
reaction mixture was heated at 100.degree. C. for 24 hour. After
the solvent was removed, the residue was washed with acetone and
extracted in a Soxlet extractor for 8 hours to afford the product
as an insoluble blue solid.
Example 5
Synthesis of
4,4-Bis-(2-ethyl-hexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene
##STR00037##
[0077] 4H-Cyclopenta[2,1-b;3,4-b]dithiophene (1.5 g, 0.00843 mol)
was dissolved in DMSO (50 mL). After the solution was purged with
nitrogen, and grounded KOH (1.89 g, 0.0337 mol), sodium iodide (50
mg), and 2-ethylhexyl bromide (3.25 g, 0.0169 mol) were
sequentially added. The reaction mixture was stirred overnight
under nitrogen (c.a. 16 hours). Water was added and the reaction
was extracted with t-butylmethyl ether. The organic layer was
collected, dried over magnesium sulfate, and concentrated. The
residue was purified by chromatography using hexanes as eluent.
Fractions containing pure
4,4-Bis-(2-ethyl-hexyl)-4H-cyclopenta[2,1-b;3,4-b]dithiophene
product were combined and concentrated. The product was obtained as
a colorless oil after drying under vacuum. Yield: 2.68 g (79%).
.sup.1H NMR (CDCl.sub.3, 250 MHz): 7.13 (m, 2H), 6.94 (m, 2H), 1.88
(m, 4H), 0.94 (m, 16H), 0.78 (t, 6.4 Hz, 6H), 0.61 (t, 7.3 Hz,
6H).
Example 6
Synthesis of
4,4-Bis-(2-ethyl-hexyl)-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-b;3,-
4-b']dithiophene
##STR00038##
[0079] Starting material
4,4-Bis-(2-ethyl-hexyl)-4H-cyclopenta[2,1-b;3,4-b]dithiophene (1.5
g, 0.00372 mol) was dissolved in dry THF (20 mL). After the
solution was cooled to -78.degree. C., butyl lithium (5.21 mL,
0.0130 mol) was added dropwise. The reaction mixture was stirred at
this temperature for 1 hour. It was then warmed to room temperature
and stirred for another 3 hours. The mixture was again cooled to
-78.degree. C. and trimethyltin chloride (1 M in hexane, 15.6 mL,
15.6 mmol) was added dropwise. The reaction mixture was allowed to
warm to room temperature and stirred overnight (c.a. 16 hours).
[0080] Water was added and the reaction was extracted with toluene.
The organic layer was washed with water, dried over sodium sulfate,
and concentrated. The residue was dissolved in toluene, and quickly
passed through a small plug of silica gel pretreated with
triethylamine. The solvent was removed and the residue was dried
under vacuum. 1.25 g of the product was obtained. .sup.1H NMR
(CDCl.sub.3, 250 MHz): 6.96 (m, 2H), 1.85 (m, 4H), 1.29 (m, 2H),
0.92 (m, 16H), 0.78 (t, 6.8 Hz, 6H), 0.61 (t, 7.3 Hz, 6H), 0.38 (m,
18H).
Example 7
Polymerization of
Bis-(trimethylstannyl)-4,4-Di(2-ethylhexyl)-cyclopenta[2,1-b:3,4-b']dithi-
ophen and 4,7-dibromo-2,1,3-benzothiadiazole
##STR00039##
[0082]
Bis-(trimethylstannyl)-4,4-di(2-ethylhexyl)-cyclopenta[2,1-b:3,4-b]-
dithiophene (0.686 g, 0.000943 mol) and
4,7-dibromo-2,1,3-benzothiadiazole (0.269 g, 0.000915 mol) were
dissolved in toluene (20 mL). After the reaction was purged with
nitrogen, tris(dibenzylideneacetone)dipalladium(0) (25.1 mg, 0.0275
mmol) and triphenylphosphine (57.6 mg, 0.220 mmol) were added. The
reaction was further purged with nitrogen for 10 minutes and heated
to 120.degree. C. under nitrogen for 24 hours. The solvent was
removed under vacuum and the residue was dissolved in chloroform.
After the mixture was poured into methanol (500 mL), the blue
precipitate thus obtained was collected by filtration, washed with
methanol, and dried. The precipitate was dissolved in chloroform
(30 mL) under heating, and filtered through a 0.45 .mu.m membrane.
The solution was loaded on to recycling HPLC (2H+2.5H column on a
Dychrome recycling HPLC, 5 cycles for each injection), in 3 mL
portions for purification. Higher-molecular-weight fractions were
combined to give 120 mg pure polymer (Mn=35 kDa).
Example 8
Copolymerization of
4,4-Dihexyl-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-b;3,4-b']dithiop-
hene,
4,4-Bis-(2-ethyl-hexyl)-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-
-b;3,4-b']dithiophene, and 4,7-Dibromo-benzo[1,2,5]thiadiazole
##STR00040##
[0084]
4,4-Dihexyl-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-b;3,4-b]di-
thiophene (0.0863 g, 0.000128 mol),
4,4-bis-(2-ethyl-hexyl)-2,6-bis-trimethylstannanyl-4H-cyclopenta[2,1-b;3,-
4-b]dithiophene (0.187 g, 0.000257 mol), and
4,7-Dibromo-benzo[1,2,5]thiadiazole (0.111 g, 0.000378 g) were
dissolved in toluene (15 mL) and the solution was degassed and
purged with N.sub.2. Tris(dibenzylideneacetone)dipalladium(0) (6.78
mg, 0.0074 mmol) and triphenylphosphine (15.5 mg, 0.0 593 mmol)
were then added. The reaction was purged again with nitrogen for 30
minutes and heated at 120.degree. C. under nitrogen. The solvent
was then removed under vacuum. The residue was dissolved in
chloroform and the solution was added into methanol. The
precipitates were collected and extracted with hexane for 24 hours
and then extracted with chloroform for 8 hours. The resultant blue
solution was concentrated and added to methanol. The precipitates
were collected to afford a first fraction of the polymer (70 mg).
The remaining materials on the thimble was further extracted with
chloroform for 20 hours. 20 mg additional polymer was
collected.
Example 9
Preparation of
4H-4,4-bis(2'-ethylhexyl)cyclopenta[2,1-b:3,4-b']thiophene-2,6-bis(pinaco-
lborate) ester
##STR00041##
[0086] 100 mL oven dried Schlenk flask was charged with 1.097 g
(2.72 mmol) of
4H-4,4-bis(2'-ethylhexyl)cyclopenta[2,1-b:3,4-b']dithiophene. The
flask was evacuated and purged with argon three times. To this
flask was then added 20 mL of dry, distilled THF. The resulting
solution was cooled to -78.degree. C. and 4.35 mL (10.88 mmol, 4
equiv.) of 2.5M BuLi was added dropwise. The reaction was stirred
for 1 hour at -78.degree. C. and then warmed to room temperature
and stirred for an additional 3 hours. The solution was cooled
again to -78.degree. C. and 2.77 mL (13.6 mmol, 5 equiv.) of
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added in
one portion via syringe. The reaction was stirred at -78.degree. C.
for 1 hour and then allowed to warm to room temperature overnight.
The solution was poured into water and extracted with 4.times.150
mL of methyl tert-butyl ether. The organic layers were combined and
washed with 2.times.150 mL of brine, dried with anhydrous
MgSO.sub.4, and filtered. The solvent was removed under vacuum to
yield and orange oil, which was purified by column chromatography
(5% EtOAc in hexanes) to yield a colorless, viscous oil, 1.34 g
(75% yield).
Example 10
Preparation of a Pentathienyl-Cyclopentadithiophene Copolymer
##STR00042##
[0088] A 50 mL Schlenk flask was charged with 0.309 g (0.472 mmol)
of
4H-4,4-bis(2'-ethylhexyl)cyclopenta[2,1-b:3,4-b']dithiophene-2,6-bis(pina-
colborate) ester prepared in Example 9, 0.367 g (0.510 mmol) of
5,5'-dibromo-3'',4''-dihexyl-a-pentathiophene (its synthesis was
described in WO 2005/092947, which is incorporated herein by
reference) 0.0013 g (0.00185 mmol) of PdCl.sub.2(PPh.sub.3).sub.2,
and 0.057 g (0.142 mmol) of trioctylmethylammonium chloride
(Aliquot 336, Aldrich, St. Louis, Mo.). The flask was fitted with a
reflux condenser and the flask was evacuated and refilled with
nitrogen three times. The solids were dissolved in 6 mL of toluene
and then 0.88 mL of 2M Na.sub.2CO.sub.3 were added via syringe. The
reaction was then heated to 95.degree. C. with stiffing for 5
hours. Phenylboronic acid (0.031 g, 0.250 mmol) and 0.0016 g
(0.00228 mmol) of PdCl.sub.2(PPh.sub.3).sub.2 were dissolved in 1
mL of THF and added to the reaction mixture, and stiffing was
continued for 16 h at 95.degree. C. The reaction mixture was
diluted with toluene (50 mL) and the organic layer was separated
and washed with warm water (3.times.50 mL). The solution was then
treated with an aqueous solution of diethyldithiocarbamic acid
sodium salt trihydrate (7.5%, DDC, 5 mL) and heated at 80.degree.
C. overnight. The aqueous layer was separated and discarded and the
organic layer was washed with warm water (3.times.50 mL) and the
polymer precipitated into methanol (500 mL). The polymer was
collected by filtration, washed with methanol (50 mL) and
redissolved in hot toluene (200 mL). The hot polymer solution was
passed through a tightly packed column of celite (1.times.8 cm),
silica get (3.times.8 cm), and basic alumina (3.times.8 cm)
(previously rinsed with 200 mL of hot toluene). The polymer
solution was collected and the volume concentrated to approximately
50 mL. The polymer was precipitated into methanol (500 mL), washed
with methanol (100 mL), acetone (100 mL) and again with methanol
(100 mL). The polymer was then dried in vacuo overnight to yield a
brick red material. Yield: 0.327 g.
Example 11
Fabrication of Solar Cell
[0089] The polymer solar cells were fabricated by doctor-blading a
blend of the polymer prepared in Example 7 (PCPDTBT) and
PC.sub.61BM or PC.sub.71BM (purchased from Nano-C, Westwood, Mass.)
in a 1:3 w/w ratio sandwiched between a transparent anode and an
evaporated metal cathode. The transparent anode was an indium tin
oxide (ITO)-covered glass substrate (Merck, Whitehouse Station,
N.J.) which was coated with a .about.60 nm thick PEDOT:PSS layer
(Baytron PH from H. C. Starck) applied by doctorblading. The
ITO-glass-substrate was cleaned by ultrasonification subsequently
in acetone, isopropyl alcohol and deionized water. The cathode, a
bilayer of a thin (1 nm) LiF layer covered with 80 nm Al, was
prepared by thermal evaporation. PCPDTBT and PC.sub.61BM or
PC.sub.71BM were dissolved together in o-dichlorobenzene (ODCB) to
give an overall 40 mg/ml solution and was stirred overnight at
60-70.degree. C. inside a glovebox. The active layer thickness, as
determined by AFM, was between 150-250 nm. Device characterization
was done under AM 1.5G irradiation (100 mW/cm.sup.2) on an Oriel
Xenon solar simulator with a well calibrated spectral mismatch of
0.98 jV-characteristics were recorded with a Keithley 2400. Active
areas were in the range of 15 to 20 mm.sup.2. EQE was detected with
a lock-in amplifier under monochromatic illumination. Calibration
of the incident light was done with a monocrystalline silicon
diode. Mobility measurements were done using an Agilent 4155C
parameter analyzer. Absorption measurements were done inside the
glovebox with an Avantes fiberoptic spectrometer or outside with a
HP spectrometer.
[0090] The interaction with PCBM and the photoinduced charge
transfer was investigated by PL quenching. The PL of pristine
PCPDTBT versus PCPDTBT/PCBM composites was measured at liquid
N.sub.2 temperatures in a cryostat, excitation was provided by an
Ar laser at 488 nm.
[0091] Electrochemical experiments were carried out on dropcast
polymer films at room temperature in a glovebox. The supporting
electrolyte was tetrabutylammonium-hexafluorophosphate
(TBAPF.sub.6, electrochemical grade, Aldrich) .about.0.1 M in
acetonitrile anhydrous (Aldrich). The working electrode (WE), as
well as the counter electrode (CE), was a platinum foil. A silver
wire coated with AgCl was used as a reference electrode (RE). After
each measurement, the RE was calibrated with ferrocene (E.sup.0=400
mV vs. NHE) and the potential axis was corrected to NHE (using
-4.75 eV for NHE.sup.24,25) according to the difference of E.sup.0
(ferrocene) and the measured E.sup.1/2 (ferrocene). .lamda..sub.max
(CHCl.sub.3)=710 nm, .lamda..sub.band edge (CHCl.sub.3)=780 nm,
band gap (CHCl.sub.3)=1.59 eV, .lamda..sub.max (film)=700-760 nm,
.lamda..sub.band edge (film)=855 nm, band gap (film)=1.45 eV,
HOMO=-5.3 eV, -5.7 eV (electrochem), LUMO=-3.85 eV, -4.25 eV,
.mu..sub.+=2.times.10.sup.-2 cm.sub.2/Vs (TOF), 1.times.10.sup.-3
cm.sup.2/Vs (FET).
[0092] Other embodiments are in the claims.
* * * * *