Influence of Top Layer Composition on the Photovoltaic Parameters of P3HT:PCBM Organic Solar Cells

Abstract

Spin and spray deposition techniques have been used sequentially to examine the effect of the composition of top blend layer on the photovoltaic properties of organic solar cells using wellknown poly(3-hexylthiophene):[6,6]-Phenyl C61 butyric acid methyl ester (P3HT:PCBM) blend. Devices were prepared by spraying an extra layer of P3HT or PCBM (~15 nm) onto spin coated (1:1) blend film. P3HT-rich top phase slightly perturbs photovoltaic activity whereas PCBM-rich top phase drastically changes the power conversion efficiencies with a marked decrease in fill factors. While the annealed devices with P3HT-rich top phases display an average of 2.3% power conversion efficiencies, the same number drops to 1.5% in devices with PCBM-rich top phases in the active layer. Carrier mobilities were only marginally affected by the presence of spray coated top layers. However, series resistance of top phase P3HT-rich blends (6 Ω/cm 2) remained the same with respect to spin coated sample whereas top phase PCBM-rich blends exhibit relatively higher series resistances for both annealed and nonannealed samples (11 Ω/cm 2). Based on the presented results, one might speculate that electron injection to cathode with P3HT is almost as efficient as with PCBM for active layers utilizing P3HT:PCBM blend.