Photovoltaic properties and charge dynamics in nanophase-separated F8T2/PCBM blend films

Abstract

We studied organic photovoltaics (OPVs) in bulk-heterojunction cells (BHJ) based on a liquid-crystalline fluorine copolymer (F8T2) with the capability of forming periodic nanostructures as the donor and a soluble fullerene (PC 70BM) as the acceptor. The surface morphology of the blend film shows that the F8T2 and PC 70BM phases are separated into large islands, which grow in size with increasing fraction of PC70BM. The power conversion efficiencies (PCEs) of the cells exhibit a distinct maximum as a fonction of the PC 70BM concentration in the BHJ OPVs; the PCE has a maximum at F8T2:PC 70BM (1:2) and decreases at both lower and higher concentrations of PC 70BM. The OPV with the highest performance has a PCE of 2.28%. In order to investigate the charge separation that occurs at the interface between F8T2 and PC 70BM, we also performed ultrafast transient absorption spectroscopy on F8T2:PC 70BM (1:2) blend films. © 2012CPST.