Charge-transfer state and charge dynamics in poly(9,9'-dioctylfluorene-co- bithiophene) and [6,6]-phenyl C 70-butyric acid methyl ester blend film

Abstract

Bulk heterojunction (BHJ) based on a donor (D) polymer and acceptor (A) fullerene derivative is a promising organic photovoltaics. Here, we performed femtosecond time-resolved spectroscopy of poly(9,9'-dioctylfluorene-co- bithiophene) (F8T2)/[6,6]-phenyl C 70-butyric acid methyl ester (PC 70BM) blend film with distinct D/A interfaces. We decomposed differential absorption spectra into fast, slow, and constant components via two-exponential fitting at respective probe photon energies. The decomposition distinguished photoinduced absorptions (PIAs) due to singlet exciton, donor polaron, and interfacial charge-transfer (CT) state. Based on these assignments, we discussed the charge dynamics in the F8T2/PC 70BM blend film. © 2011 The Japan Society of Applied Physics.