High efficiency P3HT:PCBM solar cells with an inserted PCBM Layer

By inserting a PCBM (phenyl-C61-butyric acid methyl ester) layer between a P3HT (poly(3-hexylthiophene)):PCBM blend and a Ca/Al cathode, the performance of P3HT:PCBM bulk-heterojunction polymer solar cells is greatly improved. The maximum power conversion efficiency reached 4.24%, which is much higher than that of the traditional standard P3HT:PCBM based device (3.57%). By exploring various experimental techniques including absorption spectroscopy, X-ray photoelectron spectroscopy and impedance spectroscopy, we have found that the enhancement of the device performance can mainly be attributed to two reasons: (1) the inserted-PCBM layer can enhance the overall light absorption of the whole device and hence improve the photocurrent. (2) The inserted-PCBM layer can increase the amount of PCBM at the interface between the active layer and the cathode electrode, and hence suppress carrier recombination and facilitate electron extraction.