Aggregation Strength Tuning in Difluorobenzoxadiazole-Based Polymeric Semiconductors for High-Performance Thick-Film Polymer Solar Cells

Peng Chen; Shengbin Shi; Hang Wang; Fanglong Qiu; Yuxi Wang; Yumin Tang; Jian-Rui Feng; Han Guo; Xing Cheng; Xugang Guo

doi:10.1021/acsami.8b05231

Aggregation Strength Tuning in Difluorobenzoxadiazole-Based Polymeric Semiconductors for High-Performance Thick-Film Polymer Solar Cells

ACS Appl Mater Interfaces. 2018 Jun 27;10(25):21481-21491. doi: 10.1021/acsami.8b05231. Epub 2018 Jun 13.

Authors

Peng Chen¹, Shengbin Shi¹, Hang Wang¹, Fanglong Qiu¹, Yuxi Wang¹, Yumin Tang¹, Jian-Rui Feng¹, Han Guo¹, Xing Cheng¹, Xugang Guo¹

Affiliation

¹ Department of Materials Science and Engineering and The Shenzhen Key Laboratory for Printed Organic Electronics , Southern University of Science and Technology (SUSTech) , No. 1088, Xueyuan Road , Shenzhen , Guangdong 518055 , China.

PMID: 29862815
DOI: 10.1021/acsami.8b05231

Abstract

High-performance polymer solar cells (PSCs) with thick active layers are essential for large-scale production. Polymer semiconductors exhibiting a temperature-dependent aggregation property offer great advantages toward this purpose. In this study, three difluorobenzoxadiazole (ffBX)-based donor polymers, PffBX-T, PffBX-TT, and PffBX-DTT, were synthesized, which contain thiophene (T), thieno[3,2- b]thiophene (TT), and dithieno[3,2- b:2',3'- d]thiophene (DTT) as the π-spacers, respectively. Temperature-dependent absorption spectra reveal that the aggregation strength increases in the order of PffBX-T, PffBX-TT, and PffBX-DTT as the π-spacer becomes larger. PffBX-TT with the intermediate aggregation strength enables well-controlled disorder-order transition in the casting process of blend film, thus leading to the best film morphology and the highest performance in PSCs. Thick-film PSCs with an average power conversion efficiency (PCE) of 8.91% and the maximum value of 9.10% are achieved using PffBX-TT:PC₇₁BM active layer with a thickness of 250 nm. The neat film of PffBX-TT also shows a high hole mobility of 1.09 cm² V^-1 s^-1 in organic thin-film transistors. When PffBX-DTT and PffBX-T are incorporated into PSCs utilizing PC₇₁BM acceptor, the average PCE decreases to 6.54 and 1.33%, respectively. The performance drop mainly comes from reduced short-circuit current, as a result of nonoptimal blend film morphology caused by a less well-controlled film formation process. A similar trend was also observed in nonfullerene type thick-film PSCs using IT-4F as the electron acceptor. These results show the significance of polymer aggregation strength tuning toward optimal bulk heterojunction film morphology using ffBX-based polymer model system. The study demonstrates that adjusting π-spacer is an effective method, in combination with other important approaches such as alkyl chain optimization, to generate high-performance thick-film PSCs which are critical for practical applications.

Keywords: difluorobenzoxadiazole-based polymer; polymer solar cell; temperature-dependent aggregation; thick active layer; π-spacer.