UV-ozone-treated MoO₃ as the hole-collecting buffer layer for high-efficiency solution-processed SQ：PC₇₁BM photovoltaic devices

The enhanced performance of a squaraine compound, with 2,4-bis4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl squaraine as the donor and 6,6-phenyl-C71-butyric acid methyl ester (PC₇₁BM) as the acceptor, in solution-processed organic photovoltaic devices is obtained by using UV-ozone-treated MoO₃ as the hole-collecting buffer layer. The optimized thickness of the MoO₃ layer is 8 nm, at which the device shows the best power conversion efficiency (PCE) among all devices, resulting from a balance of optical absorption and charge transport. After being treated by UV-ozone for 10 min, the transmittance of the MoO₃ film is almost unchanged. Atomic force microscopy results show that the treated surface morphology is improved. A high PCE of 3.99% under AM 1.5 G illumination (100 mW/cm²) is obtained.