Highly efficient inverted polymer solar cells based on ethanolamine-treated indium tin oxide as cathode

Significant performance enhancement has been realized for inverted polymer solar cells (PSCs) with the device structure of glass/indium tin oxide (ITO)/P3HT:PC61BM/MoO3/Ag (P3HT, poly(3-hexyl- thiophene-2,5-diyl), and PC61BM, phenyl-C61-butyric acid methyl ester) by ethanolamine (ETA)-treated ITO as cathode by spincoating. The power conversion efficiency (PCE) of the inverted PSC increases from 2.64% to 4.95% after ETA treatment, which is also higher than that of a normal device with ZnO as electron-transport layer. The surface characteristics of ETA-treated ITO were studied by contact angle, AFM, UPS, XPS, and PL measurements. As a result, ETA treatment can significantly reduce surface roughness, surface defects, surface potential, and photoexciton quenching of ITO due to the ETA molecules absorbed on the surface of ITO cathode. This facile ETA-treated surface engineering provides a promising method to enhance the performance of inverted PSCs with ITO as cathode.