Effect of solvent annealing on heterojunction polymer solar cells based on P3HT/PCBM

Heterojunction (HJ) structure has the advantages of high charge collection and transport efficiency, but it also has the disadvantage of low charge collection, due to limited p-n interfaces, compared with bulkheterojunction (BHJ) structure. In order to overcome this disadvantage of HJ, we fabricated HJ solar cells with large p-n interfaces, based on poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61- butylric acid methyl ester (PC61BM), treated by a solvent annealing (SA) process under atmospheric condition, which is a simple and low-cost process. The SA process induced a P3HT-PC61BM interdiffusion layer between the P3HT and PC61BM layers, by a diffusion of each component, and resulted in an increase of p-n interface areas. These results were confirmed by X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The performance of a HJ device fabricated with a SA process achieved a 30% higher power conversion efficiency (PCE) value (∼3.3%), than that without a SA process. Interestingly, the HJ SA device showed higher long-term stability, than that without a SA process.