Investigation of High-Performance Air-Processed Poly(3-hexylthiophene)/Methanofullerene Bulk-Heterojunction Solar Cells

High-performance bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been fabricated in ambient air. The devices treated by two-step thermal annealing exhibit power conversion efficiencies of about 3.40%, which are comparable to the devices prepared in inert atmosphere. The effect of film annealing and postannealing on the device performance has been systematically studied. The microstructure of the composite films was characterized by transmission electron microscopy. Arnbipolar field-effect transistors based on P3HT:PCBM have been fabricated to characterize the electron and hole mobilities in the composite film. An impedance analyzer has been used to investigate carrier lifetime in the solar cells. The results indicate that thermal annealing processes can control balanced electron and hole mobilities, reduce traps, and increase carrier lifetime in the organic solar cells and thus optimize the performance of the devices fabricated in air.