Pyrrolo[3,4‐c]pyrrole‐1,3‐dione‐based large band gap polymers containing benzodithiophene derivatives for highly efficient simple structured polymer solar cells

Pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (DPPD)‐based large band gap polymers, P(BDT‐TDPPDT) and P(BDTT‐TDPPDT), are prepared by copolymerizing electron‐rich 4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) unit with novel electron deficient 2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (TDPPDT) unit. The absorption bands of polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) cover the region from 300 to 600 nm with an optical band gap of 2.11 eV and 2.04 eV, respectively. The electrochemical study illustrates that the highest occupied/lowest unoccupied molecular orbital energy levels of P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) are ?5.39 eV/?3.28 eV and ?5.44 eV/?3.40 eV, respectively. The single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/P(BDT‐TDPPDT) or P(BDTT‐TDPPDT):PC70BM+DIO/Al offers a maximum power conversion efficiency (PCE) of 6.74% and 6.57%, respectively. The high photovoltaic parameters such as fill factor (～72%), open circuit voltage (V_oc, ～0.90 V), incident photon to collected electron efficiency (～76%), and PCE obtained for the PSCs made from polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) make them as promising large band gap polymeric candidates for PSC application. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3564–3574     

A vinylene‐linked benzo[1,2‐b:4,5‐b']dithiophene‐2,1,3‐benzothiadiazole low‐bandgap polymer

A new heteroarylene‐vinylene donor–acceptor polymer P(BDT‐V‐BTD) with reduced bandgap has been synthesized and its photophysical, electronic and photovoltaic properties investigated both experimentally and theoretically. The structure of the polymer comprises an unprecedented combination of a strong donor (4,8‐dialkoxy‐benzo[1,2‐b:4,5‐b']dithiophene, BDT), a strong acceptor (2,1,3‐benzothiadiazole, BTD) and a vinylene spacer. The new polymer was obtained by a metal‐catalyzed cross‐coupling Stille reaction and fully characterized by NMR, UV–vis absorption, GPC, TGA, DSC and electrochemistry. Detailed ab initio computations with solvation effects have been performed for the monomer and model oligomers. The electrochemical investigation has ascertained the ambipolar character of the polymer and energetic values of HOMO, LUMO and bandgap matching materials‐design rules for optimized organic photovoltaic devices. The HOMO and LUMO energies are consistently lower than those of previous heteroarylene‐vinylene polymer while the introduction of the vinylene spacer afforded lower bandgaps compared to the analogous system P(BDT‐BTD) with no spacer between the aromatic rings. These superior properties should allow for enhanced photovoltages and photocurrents in photovoltaic devices in combination with PCBM. Preliminary photovoltaic investigation afforded relatively modest power conversion efficiencies of 0.74% (AM 1.5G, 100 mW/cm²), albeit higher than that of previous heteroarylene‐vinylene polymers and comparable to that of P(BDT‐BTD). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Using Cyclopenta[2,1‐b:3,4‐c′]dithiophene‐4‐one as a Building Block for Low‐Bandgap Conjugated Copolymers Applied in Solar Cells

A novel electron‐accepting unit cyclopenta[2,1‐b:3,4‐c′]dithiophene‐4‐one (CPDTO‐c′), which is an isomer of CPDTO‐b′ was developed. CPDTO‐c′ can be incorporated into the D–A backbone through 5, 7 positions. The 2 position of CPDTO‐c′ can be easily functionalized with an electron‐withdrawing chain. By copolymerizing CPDTO‐c′ with four different donor units: benzo[1,2‐b:4,5‐b′]dithiophene (BDT), dithieno[3,2‐b:2′,3′‐d]silole (DTS), carbazole, and fluorene, four new conjugated copolymers P1 – P4 were obtained. All these polymers have good solubility and low‐lying HOMO energy levels (−5.41 ∼ −5.92 eV). Among them, P1 and P2 exhibit broad absorption and narrow optical bandgaps of 1.91 and 1.72 eV, respectively. Solar cells based on P1 /PC₇₁BM afforded a PCE up to 2.72% and a high V_oc up to ∼0.9 V.     

Synthesis and characterization of new low band‐gap polymers containing electron‐accepting acenaphtho[1,2‐c]thiophene‐S,S‐dioxide groups

Two donor–acceptor conjugated polymers, PTSSO‐TT and PTSSO‐BDT, composed of acenaphtho[1,2‐c]thiophene ‐ S,S‐dioxide (TSSO) as a new electron acceptor and thienothiophene (TT) or benzo[1,2‐b:4,5‐b']dithiophene (BDT) as electron donors, were synthesized with Stille cross‐coupling reactions. The number‐averaged molecular weights (M_n) of PTSSO‐TT and PTSSO‐BDT were found to be 15100 and 26000 Da, with dispersity of 1.8 and 2.4, respectively. The band‐gap energies of PTSSO‐TT and PTSSO‐BDT are 1.56 and 1.59 eV, respectively. The HOMO levels of PTSSO‐TT and PTSSO‐BDT are ?5.4 and ?5.5 eV, respectively. These results indicate that the inclusion of TSSO accepting units into polymers is a very effective method for lowering their HOMO energy levels. The field‐effect mobilities of PTSSO‐TT and PTSSO‐BDT were determined to be 1.5 × 10^?3 and 4.5 × 10^?4 cm² V^?1 s^?1, respectively. A polymer solar cell device prepared with PTSSO‐TT as the active layer was found to exhibit a power conversion efficiency (PCE) of 3.79% with an open circuit voltage of 0.71 V under AM 1.5 G (100 mW cm^?2) conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 498–506     

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     

Pyromellitic diimide‐based copolymers for ambipolar field‐effect transistors: Synthesis,characterization, and device applications

A pyromellitic diimide building block, 2,6‐bis(2‐decyltetradecyl)?4,8‐di(thiophen‐2‐yl)pyrrolo[3,4‐f]isoindole‐1,3,5,7(2H,6H)‐tetraone ( 4 ), is synthesized. Based on this building block and other electron‐rich units such as 2,2′‐bithiophene, thieno[3,2‐b]thiophene and 4,8‐bis(dodecyloxy)benzo[1,2‐b:4,5‐b′]dithiophene, three conjugated polymers P1 , P2 , and P3 are prepared in good yield via Stille coupling polymerization. These new copolymers have good solubility in common organic solvents and exhibit good thermal stability. The optical, electrochemical, and thermal properties of these polymers P1–P3 are carefully investigated, and their applications in solution‐processed organic field‐effect transistors are also studied. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2454–2464     

Low‐bandgap quinoxaline‐based D–A‐type copolymers: Synthesis,characterization, and photovoltaic properties

Three classes of quinoxaline (Qx)‐based donor–acceptor (D–A)‐type copolymers, poly[thiophene‐2,5‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diyl] P(T‐Qx), poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diy} P(BDT‐Qx), and poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(5′,8′‐di‐2‐thienyl‐2,3‐bis(4‐octyloxyl)phenyl)‐quinoxaline‐5,5‐diyl} P(BDT‐DTQx), were synthesized via a Stille coupling reaction. The Qx unit was functionalized at the 2‐ and 3‐positions with 4‐(octyloxy)phenyl to provide good solubility and to reduce the steric hindrance. The absorption spectra of the Qx‐containing copolymers could be tuned by incorporating three different electron‐donating moieties. Among these, P(T‐Qx) acted as an electron donor and yielded a high‐performance solar cell by assuming a rigid planar structure, confirmed by differential scanning calorimetry, UV–vis spectrophotometer, and density functional theory study. In contrast, the P(BDT‐Qx)‐based solar cell displayed a lower power conversion efficiency (PCE) with a large torsional angle (34.7°) between the BDT and Qx units. The BDT unit in the P(BDT‐DTQx) backbone acted as a linker and interfered with the formation of charge complexes or quinoidal electronic conformations in a polymer chain. The PCEs of the polymer solar cells based on these copolymers, in combination with [6,6]‐phenyl C70 butyric acid methyl ester (PC₇₁BM), were 3.3% [P(T‐Qx)], 1.9% [P(BDT‐Qx)], and 2.3% [P(BDT‐DTQx)], respectively, under AM 1.5G illumination (100 mW cm^?2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Effect of Extended π‐Conjugation Structure of Donor–Acceptor Conjugated Copolymers on the Photoelectronic Properties

New donor–acceptor conjugated copolymers based on alkylthienylbenzodithiophene (BDTT) and alkoxynaphthodithiophene (NDT) have been synthesized and compared with their benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based analogues to investigate the effect of the extended π conjugation of the polymer main chain on the physicochemical properties of the polymers. A systematic investigation into the optical properties, energy levels, field‐effect transistor characteristics, and photovoltaic characteristics of these polymers was conducted. Both polymers demonstrated enhanced photovoltaic performance and increased hole mobility compared with the BDT‐based analogue. However, the BDTT‐based polymer (with π‐conjugation extension perpendicular to main chain) gave the highest power conversion efficiency of 5.07 % for the single‐junction polymer solar cell, whereas the NDT‐based polymer (with π‐conjugation extension along the main chain) achieved the highest hole mobility of approximately 0.1 cm² V^?1 s^?1 based on the field‐effect transistor; this indicated that extending the π conjugation in different orientations would have a significant influence on the properties of the resulting polymers.     

Donor–acceptor‐structured naphtodithiophene‐based copolymers for organic thin‐film transistors

New donor–acceptor (D‐A) polymers, poly(4,5‐bis(2‐octyldodecyloxy)naphto[2,1‐b:3,4‐b']dithiophenebenzo[c][1,2,5]thiadiazole) (PNDT‐B) and poly(4,5‐bis(2‐octyldodecyloxy)naphto [2,1‐b:3,4‐b′]dithiophene‐4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole) (PNDT‐TBT), with the extended π‐electron delocalization of naphtho[2,1‐b:3,4‐b']dithiophene, were successfully synthesized by Suzuki and Stille coupling reactions. The structure and physical properties of polymers were characterized by DFT calculation, UV–vis absorption, cyclovoltammetry, TGA and DSC analyses. X‐ray diffraction studies indicated a relatively highly ordered intermolecular structure in PNDT‐TBT after annealing. This high degree of molecular order resulted from the crystallinity and increasing planarity, provided by the thiophene linker groups and the interdigitation of the long alkoxy side chains. The new D‐A polymer, PNDT‐TBT, exhibited a p‐type carrier mobility of 0.028 cm²/Vs and an on/off ratio of 5.9 × 10³. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 525–531     

Conjugated random terpolymers based on benzodithiophene,diketopyrrolopyrrole, and 8,10‐bis(thiophen‐2‐yl)‐2,5‐di(nonadecan‐3‐yl)bis[1,3]thiazolo[4,5‐f:5′,4′‐h]thieno[3,4‐b]quinoxaline for Efficient Polymer Solar Cell

A series of novel donor–acceptor (D–A) random conjugated terpolymers P2‐P4 along with the homopolymers P1 (BDT‐DPP) and P5 (BDT‐BTDQ) were designed and synthesized by copolymerizing a benzo[1,2‐b:4,5‐b]dithiophene (BDT) donor with an electron‐deficient diketopyrrolo[3,4‐c]pyrrole (DPP) unit and a benzothiadiazolo[3,4‐e]quinoxaline (BTDQ) moieties of different electron‐withdrawing strengths, and the resultant terpolymers showed broad absorption profile ranging from 300 to 1200 nm. The HOMO levels of the polymers were adjusted from ?5.23 to ?5.11 eV, and the optical bandgaps were controlled from 1.32 to 1.13 eV by changing the molar ratio of DPP and BTDQ acceptors. These terpolymers were used as a donor along with PC₇₁BM as an acceptor for the creation of polymer solar cells, and the performance was optimized via variable the donor to acceptor ratio and solvent vapor annealing. The polymer solar cells made from the random terpolymer P3 showed the highest overall power conversion efficiency of (9.27%), which is higher than that for the corresponding homo‐polymers counterparts, that is, P1 (7.27%) and P5 (7.68%). The results demonstrate that the designing of random D‐A1‐D‐A2 terpolymers may be the best approach for efficient polymer solar cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1478–1485     

Benzodithiophene‐based poly(aryleneethynylene)s: Synthesis,optical properties,and applications in organic solar cells

The synthesis and characterization of building block of ethynylene‐substituted benzo[1,2‐b:4,5‐b′]dithiophene (BDT), and its application in the construction of poly(aryleneethynylene)s (PAEs) are described in this article. Alkoxy‐substituted BDT and thiazolothiazole are selected as the other copolymerized units, and polymers of PEBBDT and PEBTTZ were synthesized by Pd‐catalyzed Sonogashira coupling reaction. These polymers showed intense interchain π–π interaction and deep HOMO levels (≤ ?5.50 eV). Bulk heterojunction solar cell fabricated using PEBBDT or PEBTTZ as electron donor and PC₆₁BM as acceptor display power conversion efficiency of 0.85 and 2.40%, respectively, under the illumination of AM1.5G, 100 mW cm^?2. This study shows good prospect for the application of PAEs‐type polymers in organic solar cell. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 208–215     

The new low‐band gap polymers comprising C‐, Si‐, or N‐bridged dithiophene and alkoxy‐modified 2,1,3‐benzooxadiazole units for bulk heterojunction solar cells

In this study, we used Stille coupling polymerization to synthesize a series of new low‐band gap‐conjugated polymers— PCyTBO , PCySiTBO , and PCyNTBO —comprising mainly electron‐rich C‐, Si‐, and N‐bridged dithiophene units in conjugation with electron‐deficient alkoxy‐modified 2,1,3‐benzooxadiazole moieties. The highest occupied molecular orbital energy levels of these polymers become higher as the electron‐donating ability of C‐, Si‐, or N‐bridged dithiophene units increases. These polymers also displayed excellent thermal stability and broad spectral absorptions, with PCySiTBO revealing some crystallinity. As a result, the photovoltaic device incorporating the PCySiTBO /PC₇₁BM (1:1) blend system and 1,8‐diiodooctane (2 vol %) as an additive exhibited excellent performance, under AM 1.5 G irradiation (100 mW cm^?2), with a value of V_oc of 0.64 V, a short‐circuit current density of 13.8 mA cm^?2, a fill factor of 0.57, and a promising power conversion efficiency of 5.0%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and photovoltaic properties of 2,6‐bis(2‐thienyl) benzobisazole and 4,8‐bis(thienyl)‐benzo[1,2‐B:4,5‐B′]dithiophene copolymers

In an effort to design efficient low‐cost polymers for use in organic photovoltaic cells the easily prepared donor–acceptor–donor triad of a either cis‐benzobisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole flanked by two thiophene rings was combined with the electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)‐thien‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (?5.2 to ?5.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from ?3.1 to ?3.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC₇₁BM ([6,6]‐phenyl C₇₁‐butyric acid methyl ester) as the acceptor, the trans‐benzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 316–324     

High‐performing random terpolymer‐based nonfullerene polymer solar cells fabricated using solvent additive‐free as‐cast blend films

Two new random terpolymers containing 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) as a donating unit, methyl‐3‐thiophenecarboxylate (3MT) as a weak accepting unit, and the more electron‐deficient benzo[c][1,2,5]thiadiazole (BTz) or 5,5′‐bis(2‐ethylhexyl)‐4H,4′H‐1,1′‐bithieno[3,4‐c]pyrrole‐4,4′,6,6′(5H,5′H)‐tetraone (BiTPD) unit as a third monomer (respectively yielding 3MTB and 3MTT ) were synthesized in order to achieve improved physical and optoelectronic properties relative to the 3MT‐Th copolymer bearing only BDT and 3MT. The UV–vis absorption spectra and optical bandgap energies of these terpolymers were broader and smaller than those of the 3MT‐Th copolymer. In thin films, the terpolymers displayed the face‐on polymer chain orientation, indicating that the BTz or BiTPD unit in the terpolymer backbones did not affect the molecular arrangement on the substrate. In comparison with 3MT‐Th ‐based polymer solar cells (PSCs) as control devices, the PSCs employing blend films of these terpolymers as the donor and 2,2′‐[[6,6,12,12‐Tetrakis(4‐hexylphenyl)‐6,12‐dihydrodithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,8‐diyl]bis[methylidyne(3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile] (ITIC) as the acceptor exhibited higher power conversion efficiencies (>8.0%) for the same device configuration. In addition, the 3MTB‐ and 3MTT‐ based PSC devices displayed excellent shelf‐life even after aging for over 1000 h. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1528–1535     

New quinoxaline derivatives as accepting units in donor–acceptor type low‐band gap polymers for organic photovoltaic cells

A series of new donor–acceptor‐type low‐band‐gap semiconducting polymers were synthesized as electron donors for organic photovoltaic cells. The polymers comprised quinoxaline derivatives as the acceptors and a benzodithiophene (BDT) derivative as the donors. 5,8‐Dibromoquinoxaline (Qx), 8,11‐dibromobenzo[a]phenazine (BPz), 10,13‐dibromodibenzo[a,c]phenazine (DBPz), and 8,11‐dibromo‐5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine) (CBPz) were synthesized and polymerized with 2,6‐bis(trimethyltin)?4,8‐diethylhexyloxybenzo‐[1,2‐b;3,4‐b]dithiophene (BDT) through Stille cross‐coupling to produce four types of fully conjugated semiconducting polymers: PBDT‐Qx, PBDT‐BPz, PBDT‐DBPz, and PBDT‐CBPz , respectively. Intramolecular charge transfer between the electron donating and accepting units in the polymeric backbone induced a broad absorption from 300 to 800 nm. The optical band gap energies of the polymers were measured from their absorption onsets to be 1.54–1.80 eV depending on the polymer structure. Solution‐processed field‐effect transistors were fabricated to measure the hole mobilities of the polymers, and bulk hetero‐junction photovoltaic devices were fabricated using the synthesized polymers as electron donors and fullerene derivatives as electron acceptors. One of these devices showed a high power conversion efficiency of 3.87% with an open‐circuit voltage of 0.78 V, a short‐circuit current of 9.68 mA/cm², and a fill factor of 0.51 under air mass 1.5 global (AM 1.5 G) illumination conditions (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4136–4149     

A‐D‐A Type Small Molecules Based on Boron Dipyrromethene for Solution‐Processed Organic Solar Cells

The unique properties of boron dipyrromethene (BODIPY) dyes including facile synthesis, high absorption coefficients, and delocalized molecular orbitals as well as excellent photochemical and thermal stability, make them promising as materials for organic solar cells. Accordingly, in this study three A‐D ‐A structural small molecules of BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY have been synthesized, in which two BODIPY acceptor units are symmetrically conjugated to 4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)benzo[1,2‐b:4,5‐b]dithiophene (BDTT), 9,9‐dioctyl‐9H‐fluorene (FL), and thieno[3,2‐b]thiophene (TT) donor cores, respectively. The manipulation of the structural parameters significantly improves the performances of the BHJ OSCs, which show power conversion efficiencies of 4.75 %, 1.51 %, and 1.67 % based on [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as the acceptor material and BDTT‐BODIPY, FL‐BODIPY, and TT‐BODIPY as the donor materials, respectively.     

Benzo[1,2‐b:4,5‐b′]dithiophene Building Block for the Synthesis of Semiconducting Polymers

This review covers the synthesis and polymerization of benzo[1,2‐b: 4,5‐b′]dithiophene (BDT) to generate semiconducting polymers used in organic field‐effect transistors (OFET) and organic solar cells applications.     

High‐performance fluorine‐containing BDT‐based copolymer for organic solar cells with a high open circuit voltage

A new donor–acceptor (D‐A) conjugated copolymer (PBDTT(ff)‐ttTPD) based on fluorine‐substituted benzodithiophene (BDT) and 6‐alkylthienothienyl thieno[3,4‐c]pyrrole‐4,6‐dione (ttTPD) has been synthesized via a Stille cross‐coupling reaction. As a control, the nonfluorinated BDT‐based ttTPD copolymer (PBDTT‐ttTPD) was also synthesized by using the same polymerization method. The number‐average molecular weights (M _n) of PBDTT(ff)‐ttTPD and PBDTT‐ttTPD were found to be 48,000 g/mol (? = 2.2) and 43,000 g/mol (? = 2.1), respectively. The HOMO levels of PBDTT(ff)‐ttTPD and PBDTT‐ttTPD were calculated to be ?5.65 and ?5.45 eV, respectively. The inclusion of fluorinated BDT units is a very effective approach to lowering the polymer's HOMO level. The SCLC mobilities of PBDTT(ff)‐ttTPD and PBDTT‐ttTPD were determined to be 5.9 × 10^?4 and 3.0 × 10^?4 cm²/Vs, respectively. Polymer solar cell devices prepared with PBDTT(ff)‐ttTPD and PBDTT‐ttTPD as their active layers were found to exhibit power conversion efficiencies of 7.45 and 6.79% with open circuit voltages of 0.98 and 0.84 V, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 2506–2512     

Enhancement of the Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells through a Dichlorobenzene‐Functionalized Hole‐Transporting Material

A dichlorobenzene‐functionalized hole‐transporting material (HTM) is developed for a CH₃NH₃PbI₃‐based perovskite solar cell. Notwithstanding the similarity of the frontier molecular orbital energy levels, optical properties, and hole mobility between the functionalized HTM [a polymer composed of 2′‐butyloctyl‐4,6‐dibromo‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate (TT‐BO), 3′,4′‐dichlorobenzyl‐4,6‐dibromo‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate (TT‐DCB), and 2,6‐bis(trimethyltin)‐4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐EH), denoted PTB‐DCB21] and the nonfunctionalized polymer [a polymer composed of thieno[3,4‐b]thiophene (TT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT), denoted PTB‐BO], a higher power conversion efficiency for PTB‐DCB21 (8.7 %) than that for PTB‐BO (7.4 %) is achieved because of a higher photocurrent and voltage. The high efficiency is even obtained without including additives, such as lithium bis(trifluoromethanesulfonyl)imide and/or 4‐tert‐butylpyridine, that are commonly used to improve the conductivity of the HTM. Transient photocurrent–voltage studies show that the PTB‐DCB21‐based device exhibits faster electron transport and slower charge recombination; this might be related to better interfacial contact through intermolecular chemical interactions between the perovskite and the 3,4‐dichlorobenzyl group in PTB‐DCB21.     

Synthesis and photovoltaic properties of copolymers based on benzo[1,2‐b:4,5‐b′]dithiophene and thiophene with electron‐withdrawing side chains

Six alternating conjugated copolymers ( PL1 – PL6 ) of benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thiophene, containing electron‐withdrawing oxadiazole (OXD), ester, or alkyl as side chains, were synthesized by Stille coupling reaction. The structures of the polymers were confirmed, and their thermal, optical, electrochemical, and photovoltaic properties were investigated. The introduction of conjugated electron‐withdrawing OXD or formate ester side chain benefits to decrease the bandgaps of the polymers and improve the photovoltaic performance due to the low steric hindrance of BDT. Bulk heterojunction polymer solar cells (PSCs) were fabricated based on the blend of the as‐synthesized polymers and the fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) in a 1:2 weight ratio. The maximum power conversion efficiency of 2.06% was obtained for PL5 ‐based PSC under the illumination of AM 1.5, 100 mW/cm². © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011