Bulk Heterojunction Solar Cells from Poly(3-butylthiophene)/Fullerene Blends: In Situ Self-Assembly of Nanowires, Morphology, Charge Transport, and Photovoltaic Properties

Abstract

Bulk heterojunction solar cells based on blends of regioregular poly(3-butylthiophene) (P3BT) and phenyl-C 61 -butyric acid methyl ester (PC 61 BM) were created by in situ self-assembly of P3BT nanowires and the morphology and photovoltaic properties were investigated as a function of the blend composition. Transmission electron microscopy imaging of the blends revealed an interconnected network of P3BT nanowires of 11−15 nm width and 5−10 μm length and an amorphous continuous PC 61 BM phase. The photocurrent density, fill factor, and power conversion efficiency of the P3BT nanowire/PC 61 BM solar cells varied significantly with the blend composition whereas the open circuit voltage was relatively constant (570−610 mV). A maximum power conversion efficiency of 2.52% was achieved at a 1:0.5 (wt:wt) P3BT:PC 61 BM blend ratio. The hole mobilities in the P3BT nanowire/PC 61 BM blends measured by space-charge limited current and field-effect transistors were on the order of 1 × 10 −3 cm 2 /V s and a linear dependence of current density on light intensity was observed in the blend solar cells. These results demonstrate that in situ self-assembly of polymer semiconductor nanowires as active blend component is a promising approach to the rational control of the film morphology of bulk heterojunction solar cells.