Optimization of ZnO:PEIE as an Electron Transport Layer for Flexible Organic Solar Cells

In this study, P3HT:PC61BM was utilized to fabricate flexible organic solar cells (OSCs) on the polyethylene terephthalate substrates under an ambient atmosphere. An efficient electron transport layer (ETL) was employed to achieve a better device performance. The ETL was fabricated by making a nanocomposite from zinc oxide (ZnO) and polyethyleneimine ethoxylated (PEIE). The PEIE doping causes the reduction of work function of ZnO as well as passivates the interface, which ultimately improved the performance of the solar cell. The ZnO device's performance was 0.80%, which was effectively enhanced to 0.95% after the PEIE doping with an increase in the FF and Jsc. The ZnO's reduced work function due to PEIE is responsible for easy charge conveyance from the photoactive layer to the cathode, which enhances the FF and Jsc values. Besides, the flexible OSCs with the ZnO:PEIE ETL demonstrate more improvements in the mechanical property than with ZnO. The device with the ZnO:PEIE ETL sustained around 80% of its original power conversion efficiency (PCE) after 800 bending cycles. Thus, this study can contribute to the future large-scale manufacturing of flexible OSCs by using the ZnO:PEIE ETL.