Roles of thermal annealing in cyclopentadithiophene/thienopyrroledione:fullerene blended film and performance of organic photovoltaics

The authors have attentively investigated the roles of the thermal annealing in the thin blended film of a novel low band-gap polymer poly[(4,4-bis(2-ethyl)cyclopenta- [2,1-b:3,4-b’]dithiophene)-2,6-diyl-alt-(5-octylthieo[3,4-b]pyrrole-4,6-dione)-1,3-diyl] (PCPDTTPD) and [6,6]-phenyl C60 butyric acid methyl ester (PCBM). The surface morphology, optical absorption spectra and carrier mobility of the PCPDTTPD:PCBM film as a function of annealing temperature were investigated. Open-circuit voltage as high as 0.86 V was obtained in the PCPDTTPD:PCBM active layer based organic photovoltaics. The post-deposition annealing effects on the performance of solar cells also have been discussed. The results illustrated that the maximum power conversion efficiency of 2.01% was achieved in the as-cast devices.