Interface Modification of Inverted Structure PSBTBT:PC₇₀BM Solar Cells for Improved Performance

In this paper, we demonstrate that low-temperature-processed aluminum-doped zinc oxide (AZO)/ethoxylated polyethylenimine (PEIE) electron transport layer (ETL) significantly improves the performance of poly[(4,4′-bis(2- ethylhexyl) dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3 benzothiadiazole)-4,7-diyl] (PSBTBT)-based inverted organic solar cells. Different metal oxides, including zinc oxide (ZnO), AZO, ZnO/PEIE, and AZO/PEIE, were used as ETL. The optical and morphological properties of ZnO, AZO, PEIE, and their combination layers were investigated in order to find the favorable ETLs for inverted structure PSBTBT:PC₇₀BM solar cells. Transient photocurrent, photoinduced charge extraction by linearly increasing voltage, and atomic force microscopy were performed to understand the effects of charge transport, recombination, and morphological changes on device performance. Among the various layers, including ZnO, AZO, ZnO/PEIE, and AZO/PEIE, the low-temperature-processed AZO/PEIE combination ETL was the best performing interface layer that achieved the highest device fill factor and energy conversion efficiency.