Charge generation in polymer:fullerene photovoltaic systems (Conference Presentation)

Abstract

Polymer : fullerene blend films are the best studied materials systems for organic photovoltaic energy conversion. Whilst the variety of donor materials studied is huge, the vast majority of systems use either phenyl-C61 butyric acid methyl ester (PCBM) or its C71 analogues (PC70BM) as the electron acceptor. The choice places a constraint on the donors that may be used and may exclude high oxidation potential donor materials that would otherwise be good candidates for stable photovoltaic devices. Recently, Solenne BV has developed a new ketolactam fullerene (KL) which is a stronger acceptor than PCBM. Here, we study the photocurrent generation and charge generation properties of blend devices of the new fullerene with polymers which have exhibited insufficient driving force for excitons generated in the polymer to separate into free charge carriers, when blended with PCBM or PC70BM. An example is the low LUMO benzotrithiophene-co-diketopyrrolopyrrole polymer, BTT-DPP[1,2]. We compare the external and internal quantum efficiency spectra, current-voltage characteristics and charge generation yield for polymer:PCBM and polymer:KL systems, and thereby identify the factors limiting charge generation in these systems.