Charge-Transfer State and Charge Dynamics in Poly(9,9'-dioctylfluorene-co-bithiophene) and [6,6]-Phenyl C₇₀-butyric Acid Methyl Ester Blend Film

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 C₇₀-butyric acid methyl ester (PC₇₀BM) 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/PC₇₀BM blend film. ©2011