Effect of nanostructured ZnO cathode layer on the photovoltaic performance of inverted bulk heterojunction solar cells

Inverted bulk heterojunction solar cells have recently captured high interest due to their stability and lifetime. The inverted-type configuration protects cells from the damage by oxygen and moisture in air. This has been achieved by the development of solution processable n-type semiconductors. TiO2 and ZnO are mainly used as cathode electrode layers and air stable Au electrode replaces with air sensitive Al electrode in inverted-type solar cells. In this paper, inverted bulk heterojunction solar cells are fabricated based on poly(3-hexylthiophene) (P3HT) and the N,N'-bis-dehydroabietyl-3,4,9,10-perylene dimide (PDI) materials. Solution processable ZnO cathode layer is used as electron collecting electrode. Bulk heterojunction solar cells are characterized using different blend ratios (1:1, 1:2 and 1:3) of P3HT and PDI. Nanostructured morphologies of P3HT:PDI composite films are investigated by means of Atomic Force Microscopy, which are correlated with device performance. Better device performance is observed in a flat ZnO cathode electrode layer/P3HT:PDI/Gold device configuration with the 1:3 blend ratio of P3HT:PDI film. A poly(3-hexylthiophene) (P3HT)-based inverted bulk heterojunction solar cell using PDI as acceptor is achieved an open-circuit voltage of 350 mV, current density of 0.72 mA/cm(2) leading to a power conversion efficiency (IPCE) of 8.2%. (C) 2011 Elsevier Ltd. All rights reserved.