Dithieno[3,2‐b:2′,3′‐d]pyrrole and Benzothiadiazole‐Based Semicrystalline Copolymer for Photovoltaic Devices with Indene‐C₆₀ Bisadduct

Abstract

A semicrystalline low-bandgap polymer (PDTPBT) based on alternating dithienopyrrole and benzothiadiazole moieties as a pair of the indene-C 60 bisadduct (ICBA) for polymeric solar cells is reported. The lowest unoccupied molecular orbital (LUMO) level of PDTPBT is measured to be −3.47 eV, ensuring suffi cient energy offset for photoinduced charge transfer to ICBA. Photovoltaic cells are fabricated with ICBA and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) as an acceptor. By replacing PC 71 BM with ICBA, the open-circuit voltage is increased by 0.23 V and the resulting power conversion efficiency is improved from 1.17% to 1.71%. To optimize the ICBAbased devices, crystalline low-bandgap structures should be designed carefully as a pair of ICBA by considering the energy-level offset for charge separation and crystalline interchain ordering, for minimizing the intercalated ICBAs inside the polymer domain. [+] These authors contributed equally to this work. studied extensively for applications in organic electronic and optoelectronic devices. [1][2][3][4] Considerable effort has been made to unveil the structure-properties relationships to fi ne-tune the electronic structure of conjugated polymers and optimize the device characteristics. [4][5][6][7] Recently, bulk heterojunction (BHJ) polymeric solar cells (PSCs), consisting of conjugated polymers (as a donor) mixed with C60 or C70 fullerene derivatives (as an acceptor), have shown promising performance with a power conversion efficiency (PCE) of more than ≈8%. [8][9][10][11][12][13][14][15] The structure studied most thoroughly is poly(3-hexylthiophene) (P3HT), which has shown a PCE of 4%-6.5% by optimizing the material structure (i.e., stereoregularity, etc.) and device architecture. [16][17][18][19][20][21] In particular, the incorporation of an indene-C 60 bisadduct (ICBA) has improved the PCE of P3HT-based PSCs substantially. ICBA has a higher lowest unoccupied molecular orbital (LUMO) (ca. −3.7 eV) than [6,6]-phenyl-C 61 (or C 71 )-butyric

Synthesis and photophysical properties of N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole based donor/acceptor-π-conjugated copolymers for solar-cell application

“…8,9 A series of copolymers based on DTP and various acceptors were investigated in fullerene-based organic solar cells. 10–14 However, their obtained PCEs are below 4% with poor open-circuit voltage ( V OC ), short-circuit density ( J SC ), and fill factor (FF). These results may come from the high-lying HOMO energy levels and limited light absorption, as well as the poor morphology of the blend active layer.…”

Density Functional Theoretical and Time‐dependent Density Functional Theoretical Study on Thiophene–Benzothiadiazole‐based Polymers

“…On the other hand, the introduction of an alkoxy substituent on the electron‐deficient BT moiety improves solubility while maintaining the deep HOMO level and backbone coplanarity via S⋯O noncovalent coulomb interaction (between sulfur in thiophene and alkoxy oxygen) compared to the unsubstituted T–BT structure, which also leads to good interchain π–π packing between two polymer chains. Based on these results, we have been working on the further modification of the T and BT rings while keeping the S⋯O noncovalent interaction …”

“…Figure shows the HOMO energy level of six molecules against the calculated values at various models. As in the experiments reported earlier, the HOMO level of the polymers was obtained electrochemically from the cyclovoltammetry (CV) experiments except for PCDTBT, which was taken from Ref. .…”

“…Based on these results, we have been working on the further modification of the T and BT rings while keeping the SÁ Á ÁO noncovalent interaction. 7,8 In the present study, density functional theory (DFT, Jaguar quantum chemistry software, 9 B3LYP/6-31G * * level and B3LYP/6-311G * * level) and time-dependent DFT (TD-DFT) calculations at the same levels were performed to calculate the HOMO levels and the bandgaps of the repeat units comprising T-BT alternating copolymers in order to investigate the optical and electronic properties of the polymers. Bandgaps were estimated either from the difference of the eigenvalues of the Kohn-Sham orbitals or directly from the TD-DFT calculations.…”