A Family of Donor–Acceptor Photovoltaic Polymers with Fused 4,7-Dithienyl-2,1,3-benzothiadiazole Units: Effect of Structural Fusion and Side Chains

Abstract

A new optoelectronic building block, dithieno-[3′,2′:3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole, was designed by applying a fusion strategy on 4,7-dithienyl-2,1,3benzothiadazole (DTBT) and named as fDTBT. In combination with benzo[1,2-b:4,5-b′]dithiophene (BDT), fDTBT was used for the construction of a family of donor−acceptor copolymers, P(BDT n -fDTBT), with different side chains (n is carbon number of the side chain and varies from 8, 10, 12, 16, 20, to 24). It was found that the side chains have great impact on processing and photovoltaic properties of the polymers. P(BDT n -fDTBT) (n = 8, 10, and 12) bearing small alkyl side chains show poor solubility even in hot solvents. P(BDT n -fDTBT) (n = 20 and 24) have good solubility but inferior photovoltaic performance with an efficiency of 1.04% and 0.49%, respectively. Only P(BDT 16 -fDTBT) having 2-hexyldecyl side chain possesses both suitable solution processability and good photovoltaic properties with an efficiency around 4.36%. The comparison between P(BDT 16 -fDTBT) with the nonfused reference polymer P(BDT 20 -DTBT) reveals that the structural fusion on DTBT endows the polymer a deeper HOMO energy level and a better film morphology when blending with [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM), finally resulting in improved photovoltaic performance.

Syntheses and solar cell applications of conjugated copolymers containing tetrafluorophenylene units

“…Further optimization of the ratio of BDT-tetrafluorophenylene unit may improve the morphology, hole-mobility and band gap leading to the better performance of the device. As compared to the band gap of BDT-DTBT (2.18 eV) [19], the introduction of small amount of tetrafluorophenylene unit substituting DTBT decreased the band gap (1.23e1.63 eV) significantly. In case of PTBDTDTBT also, by applying same modification, the band gap of PTBDTDTBT (1.62 eV) [20] was decreased to 1.18e1.47 eV.…”

“…The ratios of two units, BDT-DTBT and BDTtetrafluorophenylene, should be optimized to provide the proper processability, hole-mobility and band gaps. The properties of the series could be compared with the reported BDT-DTBT, with PCE value of 3.93%, which has exactly same structure as compared to our PO-BDTF except BDT-tetrafluorophenylene unit [19].…”

Design, synthesis and photophysical properties of A-D-A-D-A small molecules for photovoltaic application

“…The detailed computation is described in the Supporting Information. Due to the slight effects of the long side alkyl chain on the energy level of the whole molecule, n-octyl groups on the thiophene were simplified as the methyl groups in the model [34]. Fig.…”

Red-to-black electrochromism of 4,9-dihydro-s-indaceno[1,2-b:5,6-b’]dithiophene-embedded conjugated polymers

“…Conjugated polymers have been widely used in many areas especially in the field of organic electronics such as organic solar cells [1][2][3][4], organic light-emitting diodes [5][6][7] and organic field-effect transistors [8][9][10][11]. In recent years, conjugated polymers have also been extensively investigated as high-performance electrochromic materials [12][13][14][15][16].…”