Synthesis and Photovoltaic Properties of Thieno[3,4‐c]pyrrole‐4,6‐dione‐based donor–acceptor Copolymers

Three donor–acceptor (D–A) 1,3‐di(thien‐2‐yl)thieno [3,4‐c]pyrrole‐4,6‐dione‐based copolymers, poly{9,9‐dioctylfluorene‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, poly{N‐(1‐octylnonyl)carbazole‐2,7‐diyl‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione}, and poly {4,8‐bis(2‐ethylhexyloxyl) benzo[1,2‐b:3,4‐b′]dithiophene‐alt‐1,3‐bis(4‐hexylthien‐2‐yl)‐5‐octylthieno[3,4‐c] pyrrole‐4,6‐dione} were synthesized by Suzuki or Stille coupling reaction. By changing the donor segment, the bandgaps and energy levels of these copolymers could be finely tuned. Cyclic voltammetric study shows that the highest occupied molecular orbital (HOMO) energy levels of the three copolymers are deep‐lying, which implies that these copolymers have good stability in the air and the relatively low HOMO energy level assures a higher open‐circuit potential when they are used in photovoltaic cells. Bulk‐heterojunction photovoltaic cells were fabricated with these polymers as the donors and PC₇₁BM as the acceptor. The cells based on the three copolymers exhibited power conversion efficiencies of 0.22, 0.74, and 3.11% with large open‐circuit potential of 1.01, 0.99, and 0.90 V under one sun of AM 1.5 solar simulator illumination (100 mW/cm²). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

One donor–two acceptor (D–A1)‐(D–A2) random terpolymers containing perylene diimide,naphthalene diimide,and carbazole units

A series of one donor–two acceptor (D–A₁)‐(D–A₂) random terpolymers containing a 2,7‐carbazole donor and varying compositions of perylene diimide (PDI) and naphthalene diimide (NDI) acceptors was synthesized via Suzuki coupling polymerization. The optical properties of the terpolymers are weighted sums of the constituent parent copolymers and all show strong absorption over the 400 to 700 nm range with optical bandgaps ranging from 1.77 to 1.87 eV, depending on acceptor composition. The copolymers were tested as acceptor materials in bulk heterojunction all‐polymer solar cells using poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b;4,5‐b′]dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene)‐2,6‐diyl] (PBDTTT‐C) as the donor material. In contrast to the optoelectronic properties, the measured device parameters are not composition dependent, and rather depend solely on the presence of the NDI unit, where the devices containing any amount of NDI perform half as well as those using the parent polymer containing only carbazole and PDI. Overall this is the first example of a one donor–two acceptor random terpolymer system containing perylene diimide (PDI) and naphthalene diimide (NDI) acceptor units, and demonstrates a facile method of tuning polymer optoelectronic properties while minimizing the need for complicated synthetic and purification steps. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3337–3345     

Medium band gap conjugated polymers from thienoacene derivatives and pentacyclic aromatic lactam as promising alternatives of poly(3‐hexylthiophene) in photovoltaic application

Two alternating medium band gap conjugated polymers (PBDT‐TPTI and PDTBDT‐TPTI) derived from 4,8‐bis(4,5‐dioctylthien‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐T) or 5,10‐bis(4,5‐didecylthien‐2‐yl)dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:4,5‐b′]dithiophene (DTBDT‐T) with pentacyclic aromatic lactam of N,N‐didodecylthieno[2′,3′:5,6]pyrido[3,4‐g]thieno[3,2‐c]‐iso‐quinoline‐5,11‐dione (TPTI), are synthesized and characterized. The comparative investigation of the photostabilities of the copolymers revealed that the PDTBDT‐TPTI film exhibited the comparable photostability in relative to P3HT. Meanwhile, the inverted photovoltaic cells (i‐PVCs) from the blend films of PBDT‐TPTI and/or PDTBDT‐TPTI with PC₇₁BM, in which poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] were used as cathode modifying interlayer, presented higher power conversion efficiencies (PCEs) of 5.98% and 6.05% with photocurrent response ranging from 300 nm to 650 nm in contrast with the PCEs of 4.48% for the optimal inverted PVCs from P3HT/PC₇₁BM under AM 1.5 G 100 mW/cm². The PCEs of the i‐PVCs from PBDT‐TPTI and PDTBDT‐TPTI were improved to 7.58% and 6.91% in contrast to that of 0.02% for the P3HT‐based i‐PVCs, and the photocurrent responses of the devices were extended to 300–792 nm, when the ITIC was used as electron acceptor materials. The results indicate that the PBDT‐TPTI and PDTBDT‐TPTI can be used as the promising alternatives of notable P3HT in the photovoltaic application. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 85–95     

Conjugated polymers based on dicarboxylic imide‐substituted isothianaphthene and their applications in solar cells

Four new polymers containing a benzo[c]thiophene‐N‐dodecyl‐4,5‐dicarboxylic imide (DIITN) unit including the homopolymer and three donor–acceptor copolymers were designed, synthesized, and characterized. For these copolymers, DIITN unit with low bandgap was selected as an electron acceptor, whereas 5,5′‐(2,7‐bisthiophen‐2‐yl)‐9‐(2‐decyltetradecyl)‐9H‐carbazole), 5,5′‐(3,3′‐di‐n‐octylsilylene‐2,2′‐bithiophene), and 5,5′‐(2,7‐bisthiophen‐2‐yl‐9,9‐bisoctyl‐9H‐fluoren‐7‐yl) were chosen as the electron donor units to tune the highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) levels of the copolymers for better light harvesting. These polymers exhibit extended absorption in the visible and near‐infrared range and are soluble in common organic solvents. The relative low lying HOMO of these polymers promises good air stability and high open‐circuit voltage (V_oc) for photovoltaic application. Bulk heterojunction solar cells were fabricated by blending the copolymers with [6,6]‐phenyl‐C61‐butyric acid methyl ester or [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM). The best power conversion efficiency of 1.6% was achieved under simulated sunlight AM 1.5G (100 mW/cm²) from solar cells containing 20 wt % of the fluorene copolymer poly[5,5′‐(2,7‐bisthiophen‐2‐yl‐9,9‐bisoctyl‐9H‐fluoren‐7‐yl)‐alt‐2,9‐(benzo[c]thiophene‐N‐dodecyl‐4,5‐dicarboxylic imide)] and 80 wt % of PC71BM with a high open‐circuit voltage (V_oc) of 0.84 V. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

New low band‐gap semiconducting polymers consisting of 5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine as a new acceptor unit for organic photovoltaic cells

A new carbazole‐based electron accepting unit, 5‐(2,7‐dibromo‐9H‐carbazol‐9‐yl)benzo[a]phenazine (CBP), was newly designed and synthesized as the acceptor part of donor‐acceptor type low band‐gap polymers for polymer solar cells. The CBP was copolymerized with electron donating monomers such as benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(2‐octyl‐2‐thienyl)‐benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) through Stille cross‐coupling polymerization, and produced two alternating copolymers, PBDT‐CBP and PBDTT‐CBP. An alternating copolymer (PBDT‐CBZ) consisted of 2,7‐dibromo‐9‐(heptadecan‐9‐yl)‐9H‐carbazole (CBZ) and BDT units was also synthesized for comparison. PBDT‐CBZ showed the maximum absorption at 430 nm and did not show absorption at wavelengths longer than 513 nm. However, CBP containing polymers (PBDT‐CBP and PBDTT‐CBP) showed a broad absorption between 300 and 850 nm due to the intramolecular charge transfer interaction between the electron donating and accepting blocks in the polymeric backbone. Bulk heterojunction photovoltaic devices were fabricated using the synthesized polymers as electron donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as electron acceptor. One of these devices showed a power conversion efficiency of 2.33%, with an open‐circuit voltage of 0.81 V, a short‐circuit current of 6.97 mA/cm², and a fill factor (FF) of 0.41 under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2354–2365     

Synthesis and photovoltaic performance of donor–acceptor polymers containing benzo[1,2‐b:4,5‐b′]dithiophene with thienyl substituents

Three alternating donor–acceptor copolymers have been synthesized by Stille coupling polymerization of 2,6‐(trimethyltin)?4,8‐bis(5‐dodecylthiophene‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene with 1,3‐dibromo‐5‐hexylthieno[3,4‐c]pyrrole‐4,6‐dione, 4,7‐dibromo‐1,3‐benzothiadiazole, and 5,7‐dibromo‐2,3‐didodecylthieno[3,4‐b]pyrazine, respectively. The synthesized polymers were tested in bulk heterojunction solar cells as blends with the acceptor [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). The thienopyrroledione copolymer displayed a power conversion efficiency of 3.00% which was increased to 3.86% by application of the additive 1,8‐diiodooctane (DIO). Tapping mode atomic force microscopy analysis indicated that there was an increase in the phase separation between polymer and PCBM, leading to an improvement in the performance upon the addition of DIO. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2622–2630     

Synthesis and characterization of isoindigo‐based polymers using CH‐arylation polycondensation reactions for organic photovoltaics

A series of three new low bandgap donor–acceptor–donor–acceptor^/ (D–A–D–A^/) polymers have been successfully synthesized based on the combination of isoindigo as the electron‐deficient acceptor and 3,4‐ethylenedioxythiophene as the electron‐rich donor, followed by CH‐arylation with different acceptors (4,7‐dibromo[c][1,2,5]‐(oxa, thia, and/or selena)diazole ( 4a‐c )). These polymers were used as donor materials for photovoltaic applications. All of the polymers are highly stable and show good solubility in chlorinated solvents. The highest power conversion efficiency of 1.6% was achieved in the bulk heterojunction photovoltaic device that consisted of poly ((E)?6‐(7‐(benzo‐[c][1,2,5]‐thiadiazol‐4‐yl)?2,3‐dihydrothieno‐[3,4‐b][1,4]dioxin‐5‐yl)?6′‐(2,3‐dihydrothieno‐[3,4‐b][1,4]‐dioxin‐5‐yl)?1,1′‐bis‐(2‐octyldodecyl)‐[3,3′‐biindolinylidene]‐2,2′‐dione) as the donor and PC₆₁BM as the acceptor, with a short‐circuit current density (J_sc) of 8.10 mA/cm², an open circuit voltage (V_oc) of 0.56 V and a fill factor of 35%, which indicates that these polymers are promising donors for polymer solar cell applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2926–2933     

Alternating narrow band gap copolymers derived from indeno[1,2‐b]fluorene and thiophene‐cored‐thieno[3,4‐b]pyrazine derivatives—Synthesis,characterization and comparative studies of photochemical stability

Alternating narrow band gap (NBG) conjugated polymers derived from 6,6′,12,12′‐tetraoctylindeno[1,2‐b]fluorene (IF) and 2,3‐dimethyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTTP), 2,3‐diphenyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DPTP) or 2,3‐dioctyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DOTP), named as PIF‐DTTP, PIF‐DPTP, and PIF‐DOTP, respectively, were synthesized by Suzuki coupling reaction and characterized. The photochemical stabilities of the copolymers and copolymer derived from IF and 5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTP) were investigated by the UV absorptions, PL spectra, FT‐IR spectra, and photovoltaic properties of the copolymers as a function of UV irradiation time. The studies revealed that the degradation of thieno[3,4‐b]pyrazine (TP) ring under UV irradiation can be retarded or eliminated by introducing phenyl group into the 2,3‐positions of TP ring, and indicated that 2,3‐diphenylthieno[3,4‐b]pyrazine could be used as durable electron deficient moiety to achieve donor–acceptor NBG‐conjugated polymers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Dithienocyclopentathieno[3,2‐b]thiophene Hexacyclic Arene for Solution‐Processed Organic Field‐Effect Transistors and Photovoltaic Applications

We have developed a ladder‐type dithienocyclopentathieno[3,2‐b]thiophene ( DTCTT ) hexacyclic unit in which the central thieno[3,2‐b]thiophene ring was covalently fastened to two adjacent thiophene rings through carbon bridges, thereby forming two connected cyclopentadithiophene ( CPDT ) units in a hexacyclic coplanar structure. This stannylated Sn‐DTCTT building block was copolymerized with three electron‐deficient acceptors, dibromo‐thieno[3,4‐c]pyrrole‐4,6‐dione ( TPD ), dibromo‐benzothiadiazole ( BT ), and dibromo‐phenanthrenequinoxaline ( PQX ), by Stille polymerization, thereby furnishing a new class of alternating donor–acceptor copolymers: PDTCTTTPD , PDTCTTBT , and PDTCTTPQX , respectively. Field‐effect transistors based on PDTCTTPQX and PDTCTTBT yielded high hole mobilities of 0.017 and 0.053 cm² V^?1 s^?1, respectively, which are among the highest performances among amorphous donor–acceptor copolymers. A bulk heterojunction solar cell that incorporated PDTCTTTPD with the lower‐lying HOMO energy level delivered a higher V_oc value of 0.72 V and a power conversion efficiency (PCE) value of 2.59 %.     

Syntheses of Three New Pyridyl Thienopyridine Ligands via the Hurtley Reaction

The tridentate pyridyl thienopyridines 5‐phenyl‐7‐(pyridin‐2‐yl)thieno[2,3‐c]pyridine ( L1 ), 7‐(pyridin‐2‐yl)‐5‐(thiophen‐2‐yl)‐thieno[2,3‐c]pyridine ( L2 ) and 5,7‐di(pyridin‐2‐yl)thieno[2,3‐c]pyridine ( L3 ) have been synthesized via the Hurtley reaction. L1 and L2 were synthesized by condensing 3‐bromothiophene‐2‐carboxylic acid with phenyl‐1,3‐butanedione and 1‐thienyl‐1,3‐butanedione respectively. L3 was synthesized by condensing 3‐bromothiophene‐2‐carboxylic acid with benzoylacetonitrile. Ring closure and a subsequent Negishi or Stille cross‐coupling afforded L1 , L2 , and L3 in an overall yield of 20, 3, and 6%, respectively.     

Thieno[3,2‐b]thiophene‐substituted benzodithiophene in donor–acceptor type semiconducting copolymers: A feasible approach to improve performances of organic photovoltaic cells

Thieno[3,2‐b]thiophene‐substituted benzo[1,2‐b:4,5‐b′]dithiophene donor units (TTBDT) serve as novel promising building blocks for donor–acceptor (D‐A) copolymers in organic photovoltaic cells. In this study, a new D‐A type copolymer (PTTBDT‐TPD) consisting of TTBDT and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) is synthesized by Stille coupling polymerization. A PTTBDT‐TPD analog consisting of TTBDT and alkylthienyl‐substituted BDT (PTBDT‐TPD) is also synthesized to compare the optical, electrochemical, morphological, and photovoltaic properties of the polymers. Bulk heterojunction photovoltaic devices are fabricated using the polymers as p‐type donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as the n‐type acceptor. The power conversion efficiencies of the devices fabricated using PTTBDT‐TPD and PTBDT‐TPD are 6.03 and 5.44%, respectively. The difference in efficiency is attributed to the broad UV–visible absorption and high crystallinity of PTTBDT‐TPD. The replacement of the alkylthienyl moiety with thieno[3,2‐b]thiophene on BDT can yield broad UV–visible absorption due to extended π‐conjugation, and enhanced molecular ordering and orientation for organic photovoltaic cells. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3608–3616     

Ethynylene‐containing donor–acceptor alternating conjugated polymers: Synthesis and photovoltaic properties

Four ethynylene‐containing donor‐acceptor alternating conjugated polymers P1 – P4 with 2,5‐bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC₇₁BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (V_oc) higher than 0.8 V were obtained. P4 , with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a V_oc of 0.94 V, a J_sc of 4.2 mA/cm², an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Multichromic benzimidazole‐containing polymers: Comparison of donor and acceptor unit effects

This study reports a comparative study on electrochromic properties of two donor–acceptor–donor (DAD)‐type polymers namely poly(2‐heptyl‐4,7‐di(thiophen‐2‐yl)‐1H‐benzo [d]imidazole) (BImTh) and poly(4,7‐bis(2,3‐dihydrothieno[3,4‐b] [1,4]dioxin‐5‐yl)‐2‐heptyl‐1H‐benzo[d]imidazole) (BImEd). DAD‐type monomers were polymerized electrochemically on indium tin oxide‐coated glass slides to determine the optical properties of the polymers. Electrochemical p‐doping experiments were performed to determine the band gap and absorption band values of the polymer films at different redox states. Polymerization of BImTh and BImEd yields multichromic polymers. Donor and acceptor effects are studied by comparing the PBImEd and PBImTh with corresponding benzotriazole derivatives. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Diketopyrrolopyrrole‐based liquid crystalline conjugated donor–acceptor copolymers with reduced band gap for polymer solar cells

A new liquid crystalline (LC) acceptor monomer 2,5‐bis[4‐(4′‐cyanobiphenyloxy)dodecyl]‐3,6‐dithiophen‐2‐yl‐pyrrolo[3,4‐c]pyrrole‐1,4‐dione (TDPPcbp) was synthesized by incorporating cyanobiphenyl mesogens into diketopyrrolopyrrole (DPP). The monomer was copolymerized with bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′] dithiophene (BDT) and N‐9′‐heptadecanylcarbazole (CB) donors to obtain donor–acceptor alternating copolymers poly[4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3,6‐bis(thiophen‐5‐yl)‐2,5‐bis[4‐(4′‐cyanobiphenyloxy)dodecyl]‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione] (PBDTDPPcbp) and poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐3,6‐bis(thiophen‐5‐yl)‐2,5‐bis[4‐(4′‐cyano‐biphenyloxy)dodecyl]‐2,5‐dihydropyrrolo[3, 4‐c]pyrrole‐1,4‐dione] (PCBTDPPcpb) with reduced band gap, respectively. The LC properties of the copolymers, the effects of main chain variation on molecular packing, optical properties, and energy levels were analyzed. Incorporating the mesogen cyanobiphenyl units not only help polymer donors to pack well through mesogen self‐organization but also push the fullerene acceptor to form optimized phase separation. The bulk heterojunction photovoltaicdevicesshow enhanced performance of 1.3% for PBDTDPPcbp and 1.2% for PCBTDPPcbp after thermal annealing. The results indicate that mesogen‐controlled self‐organization is an efficient approach to develop well‐defined morphology and to improve the device performance. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and applications of 2,7‐carbazole‐based conjugated main‐chain copolymers containing electron deficient bithiazole units for organic solar cells

A series of low‐band‐gap (LBG) donor–accepor conjugated main‐chain copolymers ( P1 – P4 ) containing planar 2,7‐carbazole as electron donors and bithiazole units (4,4′‐dihexyl‐2,2′‐bithiazole and 4,4′‐dihexyl‐5,5′‐di(thiophen‐2‐yl)‐2,2′‐bithiazole) as electron acceptors were synthesized and studied for the applications in bulk heterojunction (BHJ) solar cells. The effects of electron deficient bithiazole units on the thermal, optical, electrochemical, and photovoltaic (PV) properties of these LBG copolymers were investigated. Absorption spectra revealed that polymers P1 – P4 exhibited broad absorption bands in UV and visible regions from 300 to 600 nm with optical band gaps in the range of 1.93–1.99 eV, which overlapped with the major region of the solar emission spectrum. Moreover, carbazole‐based polymers P1 – P4 showed low values of the highest occupied molecular orbital (HOMO) levels, which provided good air stability and high open circuit voltages (V_oc) in the PV applications. The BHJ PV devices were fabricated using polymers P1 – P4 as electron donors and (6,6)‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) or (6,6)‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as electron acceptors in different weight ratios. The PV device bearing an active layer of polymer blend P4:PC₇₁BM (1:1.5 w/w) showed the best power conversion efficiency value of 1.01% with a short circuit current density (J_sc) of 4.83 mA/cm², a fill factor (FF) of 35%, and V_oc = 0.60 V under 100 mW/cm² of AM 1.5 white‐light illumination. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Recent Progress in All‐Polymer Solar Cells Based on Wide‐Bandgap p‐Type Polymers

All‐polymer solar cells (all‐PSCs), with the photoactive layer exclusively composed of polymers as both donor and acceptor, have attracted growing attention due to their unique merits in optical, thermal and mechanical durability. Through the combined strategies in materials design and device engineering, recently the power conversion efficiencies of single‐junction all‐PSCs have been boosted up to 11 %. This review focuses on the recent progress of all‐PSCs comprising of wide band‐gap p‐type polymers, especially those based on the units of thieno[3,4‐c]pyrrole‐4,6(5H)‐dione], fluorinated benzotriazole, benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione, and pyrrolo[3,4‐f]benzotriazole‐5,7(6H)‐dione. Meantime, several categories of n‐type polymers used to match with these polymer donors are also reviewed. Finally, a brief summary of the strategies of molecular design and morphology optimization is given, and strategies toward further improving performance of all‐PSCs are outlined.     

Incorporation of different conjugated linkers into low band gap polymers based on 5,6‐Bis(octyloxy)‐2,1,3 benzooxadiazole for tuning optoelectronic properties

Four new 2,1,3‐benzooxadiazole‐based donor–acceptor conjugated polymers, namely poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSC), poly{9‐(9‐heptadecanyl)‐9H‐carbazole‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFC), poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(selenophen‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PSBSFL), and poly{9,9‐dioctyl‐9H‐fluorene‐alt‐5,6‐bis(octyloxy)‐4,7‐di(furan‐2‐yl)benzo[c][1,2,5]oxadiazole)}(PFBFFL), were synthesized via Stille polycondensation reaction. All polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. Their structures were verified by ¹H‐NMR and the molecular weights were determined by gel permeation chromatography (GPC). The polymer films exhibited broad absorption bands. Among all polymers, photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PSBSC:PC₇₁BM(1:3, w/w)/LiF/Al revealed an open‐circuit voltage of 0.62 V, a short circuit current of 7.63 mA cm^?2 and a power conversion efficiency of 1.89%. This work demonstrates a good example for tuning absorption range, energy level, and photovoltaic properties of the polymers with different spacers and donor units can offer a simple and effective method to improve the efficiency of PSCs. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2459–2467     

Low band‐gap modulation of isoindigo‐based copolymers toward high open‐circuit voltage of polymer solar cells

Designing low band‐gap‐conjugated polymers coupled with low HOMO levels attracts great attention in the field of polymer solar cells (PSCs). By using donor–acceptor (D‐A) copolymerization strategy, we designed and synthesized a series of low band‐gap copolymers with deep HOMO levels via introducing an isoindigo (IID) acceptor unit in the copolymers with the donor unit of fluorene (F) (PIID‐F), carbazole (Cz) (PIID‐Cz), thiophene (Th) (PIID‐Th), dithiophene (DTh) (PIID‐DTh), or dithienosilole (DTS) (PIID‐DTS). The HOMO level of the copolymers, measured by electrochemical cyclic voltammetry, varies from ?5.3 eV to ?5.8 eV, depending on different donor units in the copolymers. However, the LUMO levels of all the copolymers are fixed at about ?3.6 eV, which is mainly determined by IID acceptor unit due to its strong electron‐withdrawing ability. The new results will provide an effect help in designing IID based molecular structures. Among the copolymers, PIID‐DTS has a low band gap of 1.58 eV and possesses a low‐lying HOMO energy level of ?5.33 eV. The PSCs based on PIID‐DTS as donor and PC₇₀BM as acceptor exhibited a high open‐circuit voltage (V_oc) of 0.93 V and a primary power conversion efficiency of 2.45%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3477–3485     

Thieno[3,4‐c]pyrrole‐4,6‐dione‐3,4‐difluorothiophene Polymer Acceptors for Efficient All‐Polymer Bulk Heterojunction Solar Cells

Branched‐alkyl‐substituted poly(thieno[3,4‐c]pyrrole‐4,6‐dione‐alt‐3,4‐difluorothiophene) (PTPD[2F]T) can be used as a polymer acceptor in bulk heterojunction (BHJ) solar cells with a low‐band‐gap polymer donor (PCE10) commonly used with fullerenes. The “all‐polymer” BHJ devices made with PTPD[2F]T achieve efficiencies of up to 4.4 %. While, to date, most efficient polymer acceptors are based on perylenediimide or naphthalenediimide motifs, our study of PTPD[2F]T polymers shows that linear, all‐thiophene systems with adequately substituted main chains can also be conducive to efficient BHJ solar cells with polymer donors.     

Exploring the influence of acceptor content on semi‐random conjugated polymers

A family of diketopyrrolopyrrole (DPP)‐incorporated P3HT based semi‐random copolymers was synthesized and their optical, electronic and photovoltaic properties were investigated. For the first time, the influence of acceptor content on semi‐random copolymers was explored in the broad range of 10–40% acceptor. A mixture of DPP acceptor units with different side chains (ethylhexyl and decyltetradecyl) was incorporated into each copolymer to improve solubility and film quality. Increased DPP content in the polymer backbone resulted in broadened absorption between 350 and 900 nm, resulting in a monotonic decrease in optical band gap (E_g) of the polymers from 1.49 to 1.37 eV. Highest occupied molecular orbital (HOMO) energy levels showed an increase from 10% DPP to 20–30% DPP, while decreasing for 40% DPP. V_oc values followed a consistent trend with HOMO energy levels. Semi‐random copolymers showed significantly improved photovoltaic properties compared with P3HT. Bulk heterojunction solar cells fabricated from the semi‐random copolymers blended with PC₆₁BM exhibited high short‐circuit current densities (J_sc) up to 10.29 mA/cm² and efficiencies up to 4.43%. A new method of methanol treatment was developed and applied to the semi‐random copolymers resulting in high fill factors approaching 0.70 under ambient conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3884–3892