Vacuum-deposited PTh:C60 bulk heterojunctions with different donor–acceptor compositions were fabricated and the effect of post-production thermal annealing on their photovoltaic performance and morphology studied. We showed that co-deposition of blended mixtures leads to 60% higher photocurrents than in thickness-optimized PTh/C60 planar heterojunction counterparts [37]. Furthermore, by annealing the devices post-situ we improved their power conversion efficiency by as much as 80%, achieving performance comparable to PTh:PCBM equivalents processed in solution from thermo-cleavable precursors [52]. An enhanced photoresponse results from the favorable morphological development of PTh upon annealing, modestly larger grain sizes and increased crystallization of C60. In contrast to most small-molecule blends, annealing-induced phase separation does not lead to formation of microcrystals but rather to a controlled improvement of the donor–acceptor network. This is an inherent advantage of polymers over molecular systems.
co-deposition of blended mixtures
photocurrents
60% higher
devices
power conversion efficiency
as much as 80%