Conjugated polymers

Abstract

The present invention comprises a conjugated polymer for optoelectronic devices, comprising a structural unit of formula (I) or formula (II):
-[A-D1-A-D2]n-(I)
-[A1-D1-A2-D2]n-(II)
wherein A is an acceptor group; A1 and A2 are acceptor M groups which differ from one another; D1 and D2 are donor groups which differ from one another; and n is an integer between 30 and 1000.

Claims

1. A regioregular conjugated polymer for optoelectronic devices, comprising a structural unit of formula (I) or formula (II):
-[A-D1-A-D2].sub.n-(I)
-[A1-D1-A2-D2].sub.n-(II) wherein A is an acceptor group; A1 and A2 are acceptor groups which differ from one another; D1 and D2 are donor groups which differ from one another; and n is an integer between 30 and 1000, wherein the acceptor is an asymmetric group and the acceptor groups A are disposed with mutual symmetry about the donor group D1.

2. The polymer according to claim 1, wherein the structural unit is of formula (I) and the acceptor group, A, is selected from the group consisting of: ##STR00048## ##STR00049## wherein R is alkyl or aryl; X is S or O; Y and Z are independently selected from the group consisting of CH, CR, CF, CCl, CCF.sub.3, CCN, N, CCOOH, CCOOR and CCONHR.

3. The polymer according to claim 1, wherein the acceptor group A at each occurrence is of formula (4): ##STR00050##

4. The polymer according to claim 1, wherein D1 and D2 are independently selected from the group consisting of: ##STR00051## ##STR00052## wherein R.sup.1 to R.sup.4 are independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted aryl, and optionally substituted heterocyclyl; and p is an integer from 1 to 3.

5. The polymer according to claim 4, wherein D1 and D2 are different monomer units independently selected from structural units of formula (Xa) ##STR00053## wherein R.sup.1 to R.sup.4 are independently selected from hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted carbocyclyl, optionally substituted aryl, and optionally substituted heterocyclyl.

6. The polymer according to claim 5, wherein R.sup.3 or R.sup.4 are hydrogen.

7. The polymer according to claim 6, wherein the substituents R.sup.1 or R.sup.2 are independently selected from hydrogen or an optionally substituted alkyl chain and at least one of R.sup.1 or R.sup.2 is optionally substituted alkyl.

8. The polymer according to claim 1, wherein the polymer has a number average molar mass in the range of 40,000 to 100,000 Daltons.

9. The polymer according to claim 1, wherein the polymer comprises thiophene or phenyl endcaps.

10. The polymer according to claim 1, which is a polymer of a macromonomer comprising a structural unit of formula (XI) and a donor monomer, D2:
A-D1-A(XI).

11. The polymer according to claim 1, which is a polymer of a macromonomer comprising formula (Xla) with a donor monomer of formula (XIII):
P-A-D1-A-P(Xla)
Q-D2-Q(XIII) wherein P and Q are reactive coupling partners; and wherein the acceptor groups, A, are disposed with mutual symmetry about donor group D1.

12. The polymer according to claim 11, wherein the macromonomer is of formula (Xlb): ##STR00054##

13. The polymer according to claim 11, wherein either (a) P is selected from the group consisting of bromine, iodine and pseudo-halides; and Q is selected from the group consisting of alkenyl, B(R.sup.5).sub.2,BF.sub.3K, SiR.sup.6.sub.3, SnR.sub.3, MgX, ZnCI, ZnBr, Znl; wherein R is alkyl or aryl; R.sup.5 is selected from the group consisting of R and (OR); and R.sup.6 is chlorine, fluorine or alkyl; and X is selected from the group consisting of bromine, iodine and pseudo-halides; or (b) P is selected from the group consisting of alkenyl, B(R.sup.5).sub.2, BF.sub.3K, SiR.sup.6.sub.3, SnR.sub.3, MgX, ZnCI, ZnBr, Znl; Q is selected from the group consisting of bromine, iodine and pseudo-halides; R is alkyl; R.sup.5 is selected from the group consisting of R and (OR); R.sup.6 is chlorine, fluorine or alkyl; and X is selected from the group consisting of bromine, iodine and pseudo-halides.

14. A method of preparing a polymer according to claim 1, comprising polymerising a macromonomer of formula (Xla) with a donor monomer of formula (XIII)
P-A-D1-A-P(Xla)
Q-D.sub.2-Q(XIII) wherein P and Q are reactive coupling partners; and wherein acceptor groups, A, are disposed with mutual symmetry about donor group D1.

15. The method according to claim 14, wherein the macromonomer of formula (XI) or (Xla) is prepared by reaction of D1 with an acceptor of any one of formulae shown in claim 2 to provide selective coupling of the acceptor, one unit of acceptor on each side of the donor wherein said acceptor is coupled with mutual symmetry about donor D1.

16. A photosensitive optoelectronic device comprising one or more polymers according to claim 1.

17. The device according to claim 16, wherein the device is a photovoltaic device, a photoconductive device or a photodetector.

18. A solar cell device fabricated using one or more polymers according to claim 1 and an electron acceptor polymer or molecule.

19. The solar cell device according to claim 18, wherein the electron acceptor polymer or molecule is one or more fullerene derivatives.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic cross-section view of a bilayer photosensitive aptoelectronic device having a semiconducting layer comprising the conjugated polymer and includes FIG. 1(a) showing generation of an incitron to generate a current as shown in FIG. 1(b).

(3) FIG. 2(a) and FIG. 2(b) are schematic cross-section views of a bilayer photosensitive optoelectronic device corresponding to FIG. 1 but differing in that both semiconducting layers are photosensitive layers.

(4) FIG. 3(a) and FIG. 3(b) schematic cross-sections of a bilayer device similar to corresponding drawing of FIG. 1 but differing in that the heterojunction device is a trilayer construction.

(5) FIG. 4(a) and FIG. 4(b) are schematic cross-sections of photosensitive optoelectronic devices similar to previous figures but differing in that they contain optional change transfer/blocking layers.

(6) FIG. 5 is a graph showing the photocurrent density for a range of applied bias for polymers 5a, 5b and 5c.

(7) FIG. 6 is a graph showing the IPCE results of the polymers for a range of light wavelengths.

(8) FIG. 7 shows 2DWAXS integrations for polymers 5a, 5b and 5c.

(9) FIG. 8 shows GIWAXS integrations along the meridional plane. The stacking peak of 5c is indicated at the plot.

(10) Referring to FIG. 1, there is shown a bilayer photosensitive optoelectronic device 100 including a heterojunction device formed from a first semiconducting layer 101 and a second semiconducting layer 102 which meet at a heterojunction 103. The heterojunction device is sandwiched between first and second electrodes 104, 105. Optionally, charge transfer layers 106, 107 or blocking layers may be provided between the first and second electrodes 104, 105 and the respective first and second semiconducting layers 101, 102.

(11) The first semiconducting layer 101 is a photosensitive layer which preferably includes a conjugated polymer as described above. The first semiconducting layer 101 may be an electron donor (n-type) material or an electron acceptor (p-type) material with the second semiconducting layer including an electron acceptor (p-type) or an electron donor (n-type) material. For the sake of convenience, as shown in FIG. 1, the semiconducting material of the first layer 101 is an electron transport material, and the semiconducting material of the second layer 102 is a hole transport material. The second semiconducting layer 102 may include any type of semiconducting material, but preferably includes an organic semiconducting material, such as a semiconducting polymer, small molecules or particles or nanoparticles of semiconducting materials.

(12) In modified embodiments, the second semiconducting layer 102 and one or at least one of the optional layers 106, 107 may include a component as described above whose primary function is not to generate a photocurrent, e.g., transporting electrons or holes or charge transfer.

(13) FIG. 1(a) shows the generation of an exciton 112 when a photon 110 with energy greater than Eg-Eb is absorbed in layer 101, where Eg is the band gap of layer 101 and Eb is the exciton binding energy. The exciton 112 diffuses to the heterojunction 103 where it dissociates to form an electron 114 and hole 116. Electron 114 percolates to the negative electrode (cathode) 104 and hole 116 to the positive electrode (anode) to generate a current as shown in FIG. 1(b).

(14) The photosensitive optoelectronic bilayer device 200 of FIG. 2 is similar to that of FIG. 1 in that it has a heterojunction device formed from first and second semiconducting layers 201, 202 which meet at heterojunction 203 sandwiched between first and second electrodes 204, 205 with optional charge transfer/blocking layers 206, 207. The device 200 differs from that of FIG. 1 in that both semiconducting layers 201, 202 are photosensitive layers, and preferably at least one, more preferably both, of the layers includes a conjugated polymer as described hereinbefore. As shown, the first photosensitive layer 201 is an electron transport material which absorbs photons 210 within a first range of wavelengths (e.g. UV-visible) to product excitons 212. The second photosensitive layer 202 is a hole transport material which absorbs photons 220 within a second range of wavelengths (e.g. infrared) to produce excitons 222 (FIG. 2(a)). As in FIG. 1, the excitons 212, 222 migrate to the heterojunction 203 to form charge carriers in the form of electrons 214, 224 and holes 216, 226 which migrate to the electrodes 204, 205 to generate a current (FIG. 2(b)). As excitons 214,224 can be generated in both semiconducting layers 201, 202 to form charge carriers, there is a potential for greater currents to be generated resulting in greater efficiency.

(15) The photosensitive optoelectronic device 300 shown in FIG. 3 is similar to that of FIG. 1 in that it has a heterojunction device including first and second semiconducting layers 301, 302 sandwiched between electrodes 304, 305 with optional charge transfer/blocking layers 306, 307. The device 300 differs from FIG. 1 in that the heterojunction device is a trilayer construction with an interlayer 308 forming the heterojunction between the first and second semiconducting layers 301, 302.

(16) As shown in FIG. 3, only the first semiconducting layer 301 includes a conjugated polymer as hereinbefore described which absorbs photons 310 to produce excitons 312 (FIG. 3(a)) that dissociate at the heterojunction interlayer 308 to form electrons 314 and holes 316. The second semiconducting layer 302 is formed from a hole transport material, though it will be appreciated that the layer 302 could also include a photosensitive material including, but not limited to, a conjugated polymer as hereinbefore described. The second layer 302 preferably includes an organic semiconducting material, such as a semiconducting polymer, small molecules or particles of semiconducting material. The interlayer 308 forming the heterojunction could be formed from a single semiconducting material or a mixture/blend of semiconducting materials. The semiconducting materials for interlayer 308 may include a compound described above, small molecules, polymers, particles and/or nanoparticles.

(17) The photosensitive optoelectronic device 400 of FIG. 4 differs from the previous devices in that a single photosensitive semiconducting layer 401 is sandwiched between electrodes 404, 405, with optional charge transfer/blocking layers 406, 407 between the layer 401 and the electrodes 404, 405. The photosensitive semiconducting layer 401 preferably includes at least one photosensitive material including a conjugated polymer as disclosed herein. The layer 401 may include a single compound, but is preferably a mixture or blend of a conjugated polymer as disclosed herein with another organic semiconducting material in the form of a polymer, small molecule or particles.

(18) As shown in FIG. 4, the semiconducting layer 401 is preferably a mixture/blend including a first photosensitive material that absorbs photons 410 within a first range of wavelengths to produce excitons 412 and a second photosensitive material that absorbs photons 420 within a second range of wavelengths to product excitons 422 (FIG. 4(a)). The layer 401 preferably includes both acceptor (n-type) and donor (p-type) materials so that the heterojunction is within the semiconducting layer 401 itself. As shown in FIG. 4(b), the excitons 412, 422 dissociate within the layer 401 to form electrons 414, 424 and holes 416, 426 which migrate to the respective electrodes 404, 405 (through the optional charge transfer layers 406, 407 where provided) to generate a current.

(19) The thicknesses of each of the semiconducting layers 101, 102; 201, 202; 301, 302; 401, 402 and the interlayer 308, where provided, will typically range from about 1 nm to about 500 nm, more preferably from about 10 nm to 300 nm, and most preferably from about 40 nm to 150 nm.

(20) In further embodiments the devices may also include compounds as hereinbefore described in the form of nanocrystals or quantum dots. Additionally or alternatively, other materials in the form of nanocrystals or quantum dots may be present in addition to the conjugated polymers hereinbefore described.

(21) Macromonomers and Polymers

(22) Macromonomers and polymers were prepared as shown in Scheme 1. The synthesis procedures are described in the worked examples.

(23) ##STR00015## ##STR00016##

(24) The conjugated polymer tacticity can be controlled by using different synthesis strategies (Scheme 1). In part (a), two building blocks (3a and 3b) as electron-donating units (D1 and D2) with various substituted alkyl-chains are utilised, as well as 3,6-dibromo-5-fluoro-2,1,3-benzothiadiazole (4) as electron-accepting units (A). In part (b), by using a direct Stille cross-coupling polymerization between one equivalent of 3a (D1) and one equivalent of 4 (A), a copolymer 5a was prepared, in which the orientation of fluorine atoms on accepting units were not controlled, with bromine ortho to the fluorine or meta to the fluorine reacting randomly with compound 3a. All repeating units in the polymer backbone were completely randomly arranged as in traditional donor-acceptor copolymers [J. Am. Chem. Soc. 134, 14932-14944, (2012)]. Thus, 5a is defined as a random (A-D1) copolymer. In part (c), a step-wise cross-coupling strategy was devised based on the asymmetric reactivity of the bromine atoms on compound 4. Therefore, macro-monomer 6 was first synthesized by coupling one equivalent of 3a (D1) with two equivalents of 4 (A). The bromine meta- to the fluorine substituent in 4 was selectively coupling with 3a. This proposed regiochemistry was confirmed by 2D NMR spectroscopy. Subsequently, the macro-monomer 6 (A-D1-A) was further reacted with one equivalent of 3a (D1) or 3b (D2) via a Stille cross-coupling polymerization, yielding copolymers 5b (A-D1-A-D1) and 5c (A-D1-A-D2), in which the orientation of the fluorine atoms on the accepting units was completely controllable. This stepwise synthesis strategy could afford a symmetric orientation of fluorine atoms on the accepting units in compound 6 and subsequently a defined, regio-controlled orientation of fluorine atoms in the polymer backbone of compounds 5b and 5c. The symmetric arrangement may result in stronger intermolecular interactions and thus significantly enhanced short-circuit current density (Jsc).

(25) It is surprising that polymer 5c when synthesised by step-wise Stille cross coupling procedures exhibits number average molar mass properties (high temperature GPC-determined number average molar mass against polystyrene standards) of about 80,000-100,000 Daltons, whereas the polymer 5a prepared by traditional Stille polycondensation routinely affords material of number average molar mass of only 40,000 Daltons (by high temperature GPC against polystyrene standards).

(26) Device Preparation and Performance

(27) Organic photovoltaic devices (OPV's) were fabricated using the three polymers (5a, 5b and 5c) as electron donor and PC61BM as electron acceptor. The device structure consisted of ITO/PEDOT:PSS/polymer:PC61BM/PFN/Al. The optimized weight ratio of polymer to PC61BM is 1:1.4. About 2% (1,8-diiodooctane (DIO)/1,2-dichlorobenzene (DCB), v/v) of DIO was added as an additive for improved photovoltaic performance. There were no thermal pre- or post-annealing processes applied during the device fabrication. Device J-V characteristics are shown in FIG. 1 and parameters listed in Table 1.

(28) The devices showed the following features: (a) A high open circuit voltage VOC in the range 0.8-1.1 V (b) A high fill factor in the range 55-75% (c) A significantly improved short-circuit current density JSC from 7-9 mA/cm2 (5a), 10-12 mA/cm2 (5b) up to 14-18 mA/cm2 (5c). (d) Surprisingly high energy conversion efficiencies for polymer 5c having A-D1-A-D2 type repeating units. (e) Strong evidence for A-D1-A-D2 type conjugated polymers providing more accurate control and design of the structure of repeating units in comparison with typical A-D type polymers, indicating obvious advantages in tailoring numerous polymer properties, including energy levels, side-chain sizes and lengths, backbone tacticity, intermolecular aggregates, thermal and chemical stabilities, polymer solubilities, processing conditions, etc. (f) Devices containing fullerene derivatives blended with polymer 5c show good device stability when thermally treated at up to 80-120? C. This is particularly advantageous for device fabrication in roll-to-roll printing where thermal treatment is often required for efficient layer by layer deposition of materials.

(29) TABLE-US-00001 TABLE 1 Photovoltaic properties of the OPVs based on 5a- 5c/PC.sub.61BM and hole mobilities of the polymers. V.sub.OC J.sub.SC FF PCE (%) ?.sub.hole Polymer (V) (mA/cm.sup.2) (%) Best Ave.sup.[a] (cm.sup.2V.sup.?1s.sup.?1).sup.[b] 5a 0.89 ?7.25 60.56 3.91 3.74 2.3 ? 10.sup.?5 5b 0.90 ?10.82 60.81 5.92 5.67 2.0 ? 10.sup.?4 5c 0.90 ?14.20 61.05 7.80 7.38 1.5 ? 10.sup.?3 .sup.[a]Averaged from 40 devices. .sup.[b]Measured by using the space-charge-limited current (SCLC) method.

(30) FIG. 5 of the drawings shows the OPV performance of 5a-5c polymers. a, Photocurrent density-voltage (J-V) curves of 5a (square), 5b (round) and 5c (triangle) under illumination of AM 1.5G, 100 mW cm?2.

(31) FIG. 6 of the drawings shows IPCE results of corresponding OPVs, 5a, 5b and 5c using the same identification.

(32) Selection of material with number average molar mass in the range 75,000-100,000 Daltons affords surprisingly high solar cell device efficiencies. For example a solar cell device fabricated with conventional geometry configuration using a 1:1.4 w/w blend of polymer 5c with PC61BM exhibits energy conversion efficiency of 7.8% compared with efficiencies of 3.9% for 5a and 5.9% for 5b using exactly the same fabrication conditions.

(33) It is expected that A-D1-A-D2 type conjugated polymers can replace typical A-D conjugated polymers, since the A-D1-A-D2 materials provide more controllable tailoring of polymer structures and thus more desirable bulk heterojunction morphology when blended with fullerene derivatives. Nanoscale domains with higher crystallinity may be present imparting improved charge transport. In addition, the A-D1-A-D2 conjugated polymers give higher molecular weight compared with traditional A-D polymers. This makes the material particularly suited for roll-to-roll fabrication of large area solar cell devices.

(34) Improving the J.sub.SC value of a photovoltaic device by means of molecular design has been realized using a stepwise approach. Applying asymmetric fluorine substitution to the building block has been proven to be an effective method to control the tacticity of polymer backbones as well as the size of pendant groups, which directly affects the intermolecular packing and interactions in a polymer/fullerene bulk-heterojunction layer. The well-ordered morphology in the polymer domain can dramatically increase the charge carrier mobility and thus J.sub.SC value. Based on the 5c polymer and PC.sub.61BM derivative system, photovoltaic devices with a PCE higher than 7% have been realised through design of a high performance polymer.

(35) In one embodiment, the inventors have found that a conjugated polymer having a structure of formula (I) comprising asymmetric fluorine acceptors exhibit improved performance over typical A-D-A-D type conjugated polymers (regioregular or random). The regioregular polymers of formula (I) enables variations in the donor moieties which allows tailoring of polymer regiochemistry and solubility. Without being bound by theory, the improved performance, in part may be attributed to improved intermolecular ?-stacking interactions which enhance charge-carrier mobility and is supported by X-ray diffraction measurements.

(36) X-Ray Diffraction in Bulk Solid State

(37) Random copolymer 5a and regioregular copolymers 5b and 5c in the bulk solid state were characterised using two-dimensional, wide angle X-ray scattering (2D-WAXS) techniques. The measurement procedures are described in the worked examples. Fibres of the neat polymers 5a-c were macroscopically aligned by extrusion and no further thermal pre- or post-annealing processes were performed in order to ensure the polymers undergo the same thermal treatment during device fabrication. The polymers at 30? C. exhibited characteristic reflections distributed in the equatorial and meridional planes. FIG. 7 shows 2DWAXS integrations for polymers 5a, 5b and 5c

(38) Polymers 5a and 5b showed equatorial small-angle reflections which were attributed to a chain-to-chain distance of 19.65 ?, the broad equatorial wide-angle scattering reflection (on the same plane) was attributed to a stacking distance of 4.18 ? and the meridional, middle-angle scattering reflection exhibited a d-spacing distance of 12.0 ? for 5a and 12.65 ? for 5b, corresponding to the single thienyl-dithiophene repeat unit distance.

(39) In contrast, polymer 5c exhibited sharper, more distinct and a higher number of reflections with a chain-to-chain distance of 24.51 ? and a significantly smaller stacking distance of 3.66 ?. Polymer 5c exhibited a similar single thienyl-dithiophene repeat unit distance of 12.8 ?. Therefore, 2D-WAXS measurements show significantly closer packing and higher crystallinity for regioregular asymmetric polymer 5c.

(40) X-Ray Diffraction on Thin Films

(41) Thin films of polymers 5a-c were prepared to analyse their surface organisation in the solar cell. The thin films were prepared in the same manner as for the devices including the PEDOT:PSS surface, blending with PC61BM and 1,8-diiodooctane to replicate polymer organisation in an OPV device. Grazing incidence WAXS (GIWAXS) on the thin films using the polymers 5a-c was performed. The meridional position of the wide-angle scattering intensity at qxy=0 ??1 and qz=1.72 ??1 in the spectra for 5c as shown in FIG. 6 was attributed to a stacking distance of 3.66 ?, which is characteristic for a face to face arrangement of the backbones toward the surface. In accordance with this alignment the chain-to-chain reflections appeared in the small-angle equatorial plane. Additional meridional small-angle reflections were due to an edge-on arrangement of a certain misaligned polymer fraction leading to a mixed organisation with a coexistent face- and edge-on arrangement in the film. Without being bound by theory, it is possible that a face-on polymer arrangement favors the charge carrier transport perpendicular to the solar cell surface as is the case in a solar cell device. In contrast, 5a and 5b exhibit only a meridional small-angle scattering reflection and no ?-stacking reflection indicating low order in edge-on arranged polymer layers. Therefore, with respect to both factors, X-ray diffraction data shows better packing and face-on arrangement for polymer 5c which may be more optimised for solar cell applications and shows improved performance. FIG. 8 b shows the GIWAXS integrations along the meridional plane.

EXAMPLES

Example 1

Monomer Synthesis

2-Ethylhexyl-3-hexyl thiophene (1a)

(42) 100 mL of (2-ethylhexyl) magnesium bromide (1.0M in diethyl ether) solution was added dropwise to a reaction mixture of 22 g (0.09 mol) of 2-bromo-3-hexylthiophene, and 0.001 mol Ni(dppp)Cl.sub.2 in 50 mL of anhydrous THF cooled in an ice bath. After addition, the brown solution was allowed to warm to room temperature, with stirring. An exothermic reaction starts within 30 minutes, and the ether begins to reflux gently. After stirring for 2 hours at room temperature, most of the magnesium bromide salt has deposited. The mixture is refluxed with stirring for overnight. Upon cooling to room temperature, the reaction mixture was poured into a mixture of crushed ice and diluted HCl (2N) and extracted from ether. The combined organic layer was dried over MgSO.sub.4. After filtration, the solvent was removed by rotary evaporation to afford brown oil that was purified by column chromatography on silica gel with n-heptane as eluent. The final product was obtained by using distillation under high vacuum, providing 20.0 g colourless oil in yield 87%.

(43) .sup.1H NMR (400 MHz, CDCl.sub.3) ? 7.01 (d, J=5.2Hz, 1H), 6.791 (d, J=5.2 Hz, 1H), 2.63 (d, J=7.1 Hz, 2H), 2.52-2.43 (m, 2H), 1.73-1.41 (m, 3H), 1.36-1.10 (m, 14H), 0.95-0.80 (m, 9H). .sup.13C NMR (100 MHz, CDCl.sub.3) ? 138.38, 137.72, 128.51, 121.09, 41.71, 32.51, 31.96, 31.73, 30.82, 29.24, 28.86, 28.32, 25.65, 23.02, 22.61, 14.09, 14.06, 10.84.

4,8-Di(2-(2-ethylhexyl)-3-hexylthiophen-5-yl)-benzo[1,2-b:4,5-b]dithiophene (2a)

(44) Compound 1a (8.4 g, 30 mmol) was dissolved in anhydrous THF (30 mL) in a three-neck flask under an argon atmosphere. The solution was cooled to 0? C., and a solution of n-BuLi (1.6 M in hexane, 20 mL, 32 mmol) was added dropwise with stirring. The reaction mixture was then heated to 50? C. for 2 hours. Subsequently, 4,8-dehydrobenzo[1,2-b:4,5-b]dithiophene-4,8-dione (2.20 g, 10 mmol) was quickly added, and the reaction mixture was stirred at 50? C. for 2 hours. Then the reaction mixture was cooled to ambient temperature. A solution of SnCl.sub.2 (15.2 g, 80 mmol) in 10% HCl (20 mL) was then added. The reaction mixture was stirred for an additional 1.5 hours and poured into ice water. The mixture was extracted twice with petroleum ether. The organic phase was dried over MgSO.sub.4 and concentrated. The crude product was purified by silica gel chromatography using petroleum ether as the eluent to yield the pure product as a yellowish viscous solid (5.23 g, 70% yield).

(45) .sup.1H NMR (400 MHz, CDCl.sub.3) ? 7.66 (d, J=5.7 Hz, 2H), 7.43 (d, J=5.7 Hz, 2H), 7.20 (s, 2H), 2.73 (d, J=7.1 Hz, 4H), 2.64-2.49 (m, 4H), 1.62 (m, 6H), 1.47-1.22 (m, 28H), 0.99-0.85 (m, 18H). .sup.13C NMR (100 MHz, CDCl.sub.3) ? 139.14, 138.82, 138.79, 138.76, 136.32, 135.30, 129.69, 127.26, 124.11, 123.53, 41.71, 32.66, 32.23, 31.77, 30.79, 29.23, 28.92, 28.42, 25.90, 23.03, 22.65, 14.14, 14.12, 14.09, 10.94. m/z (MALDI-TOF) 745.8 calcd. for C.sub.46H.sub.66S.sub.4 746.4.

2,6-Bis(trimethyltin)-4,8-di(2-(2-ethylhexyl)-3-hexylthiophen-5-yl)-benzo[1,2-b:4,5-b] dithiophene (3a)

(46) Compound 2a (5.0 g, 6.7 mmol) was dissolved anhydrous THF (60 mL) in a two-neck flask under the protection of argon. The solution was cooled to 0? C., and a solution of n-BuLi (1.6 M in hexane, 10 mL, 16 mmol) was added dropwise with stirring. After this addition, the reaction mixture was warmed to ambient temperature and stirred for 2 hours. Then the reaction mixture was cooled to 0? C. and a SnMe.sub.3Cl solution (1 M in THF, 20 mL, 20 mmol) was added in one portion. The reaction mixture was stirred at 0? C. for 30 minutes and then warmed to room temperature for 8 hours. Subsequently, the reaction mixture was pour into petroleum ether, washed by KF saturated aqueous solution twice and water twice. Then, the organic layer was dried over MgSO.sub.4 and concentrated to afford the yellow crude product. The crude product was further purified by recycle GPC system and finally afforded straw yellow sheet-shaped crystals (6.4 g, 89% yield).

(47) .sup.1H NMR (400 MHz, CDCl.sub.3) ? 7.76 (s, 2H), 7.26 (s, 2H), 2.77 (d, J=7.1 Hz, 4H), 1.90-1.86 (m, 4H), 1.71-1.67 (m, 2H), 1.50-1.35 (m, 32H), 1.00-0.92 (m, 18H), 0.42 (s, 18H). .sup.13C NMR (100 MHz, CDCl.sub.3) ? 145.37, 143.08, 141.89, 138.78, 138.64, 138.62, 137.14, 135.99, 131.38, 129.61, 127.51, 125.25, 122.46, 41.66, 32.68, 32.28, 31.84, 30.77, 29.19, 28.95, 28.40, 25.98, 23.06, 23.02, 22.67, 14.15, 14.13, 11.00, 10.95. m/z (MALDI-TOF) 1071.5 calcd. for C.sub.52H.sub.82S.sub.4Sn.sub.2 1072.3.

(48) The synthesis of the compound 3b was performed using 2-ethylhexyl thiophene 1b under the same conditions as for 3a, reported by Huo, L. J. et al [Angew. Chem. Int. Ed. 50, 9697-9702 (2011)].

(49) The synthesis of the compound 4 was as published by Van der Poll, T. S. et al [Adv. Mater. 24, 3646-3649 (2012)].

2,6-(Bis-4-(6-fluoro-7-bromo)benzo[c][1,2,5]thiadiazole))-4,8-di(2-(2-ethylhexyl)-3-hexyl thiophen-5-yl)-benzo[1,2-b:4,5-b]dithiophene (6, A-D1-A)

(50) Compound 3a (2.15 g, 2 mmol) and 4 (1.56 g, 5 mmol) were dissolved in toluene (100 mL) in a two-neck flask under the protection of argon. After adding Pd(PPh.sub.3).sub.4 (115 mg, 0.1 mmol) as catalyst, the reaction mixture was stirred and heated to reflux for 16 h. The solution was poured into water (50 mL) with vigorous stirring and the aqueous layer was extracted with dichloromethane. The combined organic layer was dried with MgSO.sub.4 and then rotary evaporated to remove the solvent. The dark red crude product was purified by column chromatography on silica gel with dichloromethane/n-heptane (40:60) as eluent, affording purple crystals as pure product (2.2 g, 90% yield).

(51) .sup.1H NMR (500 MHz, C.sub.2D.sub.2Cl.sub.4, 120? C.) ? 8.95 (s, 2H), 7.79 (d, J=9.8 Hz, 2H), 7.44 (s, 2H), 2.91 (d, J=6.7 Hz, 4H), 2.76 (t, J=7.4 Hz, 4H), 1.83 (d, J=7.1 Hz, 4H), 1.60-1.56 (m, 12H), 1.52-1.35 (m, 18H), 1.08-1.05 (t, J=7.3 Hz, 6H), 1.01-0.92 (m, 12H). .sup.13C NMR (125 MHz, C.sub.2D.sub.2Cl.sub.4, 120? C.) ? 161.50, 159.50, 154.36, 149.15, 139.98, 139.16, 139.04, 138.26, 137.97, 134.44, 130.31, 127.61, 127.53, 126.97, 125.03, 117.71, 117.46, 97.50, 97.30, 41.76, 33.01, 32.54, 31.57, 30.45, 29.00, 28.94, 28.36, 26.30, 22.76, 22.34, 13.66, 13.63, 10.90. m/z (MALDI-TOF) 1208.0 calcd. for C.sub.58H.sub.66Br.sub.2F.sub.2N.sub.4S.sub.6 1208.2.

(52) General Method of Stille-Coupling Polymerization for Random Polymers

(53) In a glove box, the monomer 3a (or 3b) (1 mmol) and monomer 4 (1 mmol) were mixed in a microwave reaction tube. After being dissolved in 5 mL of chlorobenzene, Pd(PPh.sub.3).sub.4 (50 ?mol) was added as the catalyst, and the tube was sealed with a Teflon? cap. The reaction mixture was heated to 100? C. for 1 minute, 135? C. for 1 minute, 170? C. for 1 hour, and 200? C. for 20 minutes using a Biotage microwave reactor. Then the achieved polymer was end-capped by reacting with 0.2 mL 2-(tributylstannyl)thiophene and 0.2 mL 2-bromothiophene at 170? C. for 20 minutes, respectively. The end-capped polymer was precipitated by addition of 50 mL methanol, filtered through a Soxhlet thimble. The precipitate was then subjected to Soxhlet extraction with acetone, ethyl acetate, n-heptane, dichloromethane and chloroform. The polymer was recovered as solid from the chloroform fraction by precipitation from methanol. The solid was dried under vacuum. The yield and HT-GPC results of the polymers are sown below.

(54) General Method of Stille-Coupling Polymerization for Symmetric Polymers

(55) In a glove box, the monomer 3b (0.5 mmol) and monomer 6 (0.5 mmol) were mixed in a microwave reaction tube. After being dissolved in 5 mL of chlorobenzene, Pd(PPh.sub.3).sub.4 (50 ?mol) was added as the catalyst, and the tube was sealed with a Teflon? cap. The reaction condition and purification process were similar to random polymers. The yield and HT-GPC results of the polymers are as follows. 5a (A-D1). Yield 76%, dark purple solid, M.sub.n=31 kDa, PDI=2.2, T.sub.d=390? C. 5b (A-D1-A-D1). Yield 87%, dark purple solid, M.sub.n=46 kDa, PDI=2.2, T.sub.d=397? C. 5c (A-D1-A-D2). Yield 89%, dark purple solid, M.sub.n=76 kDa, PDI=2.2, T.sub.d=400? C.
Device Fabrication and Characterization

(56) OPV Device Preparation: ITO-coated glass substrates (Lumtec, 5? sq.sup.?1) were cleaned by successively sonicating in detergent, Milli-Q water, acetone and iso-propanol (each 10 min). The substrates were then exposed to a UV-ozone clean (Novascan PDS-UVT, 10 min). PEDOT/PSS (HC Starck, Baytron P Al 4083) was filtered (0.2 ?m RC filter) and deposited by spin-coating (5000 rpm, 20 s). The PEDOT/PSS layer was then annealed on a hotplate in air (150? C., 10 min).

(57) For devices with spin-coated active layers, PDTBDTFBT polymer and PC.sub.61BM (w/w=1:1.4) were dissolved in 1,2-dichlorobenzene (Aldrich, anhydrous) with 2% (v/v) DIO as additive and deposited onto PEDOT:PSS coated substrates inside a glovebox by static spin-coating (900 rpm, 2 mins). The concentration and spin speed were optimised to match the film thickness of 100 nm. These devices were kept in a glove box overnight until all solvent evaporated, spin-coated with an interfacial PFN layer (0.5 mg/mL in methanol, 5000 rpm, 30s), as described in Huang, F. Novel electroluminescent conjugated polyelectrolytes based on polyfluorene, Chem. Mater. 16, 708-716 (2004), then transferred (without exposure to air) to a vacuum evaporator (Angstrom Engineering Inc.) equipped with a variety of masks and a gradient shutter. Subsequently, an Al electrode was deposited without breaking vacuum at pressures below 1?10.sup.?6 mbar and at a rate of 1 ? s.sup.?1. The area defined by the shadow mask gave device areas of 2 mm?5 mm. A device schematic is shown below.

(58) ##STR00017##

(59) The completed devices were then encapsulated with glass and a UV-cured epoxy (Summers Optical, Lens Bond type J-91) by exposing to 365 nm UV light inside a N.sub.2 glovebox (10 min). The encapsulated devices were then removed from the glovebox and tested within 1 h.

(60) Current-Voltage (J-V) Characteristics: OPV cells were tested with an Oriel solar simulator fitted with a 1000 W Xe lamp filtered to give an output of 100 mW cm.sup.?2 at AM 1.5G, The lamp was calibrated using a standard, filtered Si cell from Peccell Limited which was subsequently cross-calibrated with a standard reference cell traceable to the National Renewable Energy Laboratory. The devices were tested using a Keithley 2400 Sourcemeter controlled by Labview software. The J-V characteristics of the solar cells were measured and device performance extracted from the J-V data.

(61) IPCE Measurements: IPCE ratio data was collected using an Oriel 150 W Xe lamp coupled to a monochromator and an optical fibre. The output of the optical fiber was focussed to give a beam that was contained within the area of the device. IPCE data was calibrated with a standard, unfiltered Si cell.

(62) Space-Charge-Limited Current (SCLC) Mobility Measurement: The exact same device configuration as in working devices was used in the single carrier devices except that in the hole-only devices, Al was replaced by high work function MoO.sub.3/Au as the cathode; and in electron-only devices, a titanium(IV) oxide bis(2,4-pentanedionate) (TOPD) layer [Wang, F. Z. et al. Org. Electron. 13, 2429-2435 (2012)] was inserted between PEDOT:PSS and the active layer.

(63) X-Ray Diffraction Measurements

(64) 2D-WAXS: 2DWAXS measurements were performed using a rotating anode (Rigaku 18 kW), Osmic confocal MaxFlux optics, X-ray beam with pinhole collimation and a MAR345 image plate detector. The samples were prepared as a thin filament of 0.7 mm in diameter via filament extrusion at 80? C. For the measurements, the samples were positioned perpendicular to the incident X-ray beam and vertical to the 2D detector.

(65) GIWAXS: GIWAXS measurements were performed using a custom setup consisting of a Siemens Kristalloflex X-ray source (copper anode X-ray tube operated at 30 kV and 20 mA), Osmic confocal MaxFlux optics and a three pinhole collimation system (JJ X-ray). The samples were prepared according to the conditions for device fabrication (see above for details OPV device preparation) on top of 1?1 cm silicon substrates and were irradiated at the incident angle (?.sub.i) of 0.20?.

Examples 2 to 11

(66) Conjugated polymers of Examples 2 to 11 shown in Table 2 are prepared by reaction of the A-D-A macromonomer with monomer D2 (each provided with terminal coupling partners [in accordance with formula (XIa) and (XII)] as shown in Table 2 using the general approach shown in Scheme 1 above for preparation of compound 5c.

(67) Methods which are used may include Stille-coupling polymerisation and Suzuki-coupling polymerisation as described in the following general methods.

(68) General Method of Stille-Coupling for A-D1-A Macromonomer:

(69) Compound D1 (2 mmol, 1 eq.) and A (5 mmol, 2.5 eq.) were dissolved in toluene (100 mL) in a two-neck flask under the protection of argon. After adding Pd(PPh.sub.3).sub.4 (0.1 mmol, 5% eq.) as the catalyst, the reaction mixture was stirred and heated to 80? C. for 16 h. The solution was poured into water (50 mL) with vigorous stirring and the aqueous layer was extracted with dichloromethane. The combined organic layers were dried with MgSO.sub.4 and then rotary evaporated to remove the solvent. The dark red crude product was purified by column chromatography on silica gel with dichloromethane/n-heptane as eluent, affording crystals as pure product (80-90% yield).

(70) General Method of Stille-Coupling Polymerization for Symmetric Polymers

(71) In a glove box, the monomer D1 (or D2) (0.5 mmol) and monomer A-D1-A (0.5 mmol) were mixed in a microwave reaction tube. After being dissolved in 5 mL of o-xylene, Pd.sub.2(dba).sub.3 (20 ?mol) and tri(o-tolyl)phosphine (80 ?mol) was added as the catalyst, and the tube was sealed with a Teflon? cap. The reaction mixture was heated to 100? C. for 1 minute, 135? C. for 1 minute, 170? C. for 1 hour, and 200? C. for 20 minutes using a Biotage microwave reactor. The resulting polymer was end-capped by reacting with 0.2 mL 2-(tributylstannyl)thiophene and 0.2 mL 2-bromothiophene at 170? C. for 20 minutes, respectively. The end-capped polymer was precipitated by addition of 50 mL methanol and filtered through a Soxhlet thimble. The precipitate was then subjected to Soxhlet extraction with acetone, ethyl acetate, n-heptane, dichloromethane and chloroform. The polymer was recovered as a solid from the chloroform fraction by precipitation from methanol. The solid was dried under vacuum. The yield and HT-GPC results of the polymers are given below.

(72) General Method of Suzuki-Coupling Polymerization for Symmetric Polymers

(73) In a glove box, the monomer D1 (or D2) (0.5 mmol) and monomer A-D1-A (0.5 mmol) were mixed in a microwave reaction tube. After being dissolved in 5 mL of o-xylene, the solution was blend with 5 mL 2M K.sub.2CO.sub.3 aqueous solution and 2 drops of Aliquat 336. Under agron atmosphere, Pd(PPh.sub.3).sub.4 (20 ?mol) was added as the catalyst, and the tube was sealed with a Teflon? cap. The reaction condition and purification processes were similar to those used for the Stille-coupling polymers.

A-D1-A and D2 Examples

(74) TABLE-US-00002 TABLE No A-D1-A D2 2 3 0 4 5 6 7 8 0 9 10 11 No A-D1-A-D2 2 3 4 0 5 6 7 8 9 10 11