Ultrafast photoexcited dynamics probe of blends of conjugated polymer poly{bi(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione} and fullerenes for photovoltaic applications with broadband sub-10-fs visible pulse

Abstract

Conjugated polymers have been widely studied as active materials for organic solar cells, which are a promising replacement for silicon solar cells. A novel electron donor polymer of poly{bi(dodecyl)thiophene-thieno[3,4-c]pyrrole-4,6-dione} (PBTTPD) blended with an electron acceptor, [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM), gave a device power conversion efficiency as high as 7.3%. In the present work, we performed time-resolved absorption change spectroscopy at various mixture ratios of PC71BM in the PBTTPD/PC71BM blend. Among the obtained time constants, the shortest (60 fs) and the longest (500 fs and 15 ps) were assigned to the production and relaxation of charge-transfer (CT) states, respectively. The PC71BM blended with PBTTPD was found to suppress interchain carrier transport and increase intrachain carrier transport. The prolonged lifetime of the CT state in the equally blended PBTTPD/PC71BM film increases the probability of charge separation and thus increases the power conversion efficiency of the device. (C) 2016 The Japan Society of Applied Physics