3/Ag/MoO 3 multilayer transparent electrodes for organic solar cells by using UV–ozone treated MoO 3 layer]]>

摘要

Ultraviolet ozone (UVO) treatment of molybdenum trioxide (MoO3) appears to be a simple and efficient method for obtaining highly continuous and smooth silver (Ag) thin films in the thermally evaporated MoO3/Ag/MoO3(MAM) multilayered structure as transparent electrodes for small-molecule organic solar cells (OSCs). It is observed that UVO treatment can oxidatively modify the non-stoichiometric MoO3(or MoO3-x) surfaces, further increasing the Mo6+/Mo5+composition ratio and work function of MoO3-x. Importantly, the use of UVO treatment for the MoO3bottom layer effectively improves the wettability of Ag on MoO3and enhances the lateral growth of Ag thin film, resulting in a reduction of the percolation threshold thickness of the continuous Ag layer. Due to the formation of an ultrathin Ag interlayer with a continuous and smooth surface morphology, the MAM multilayered electrode after UVO treatment of MoO3for 3?min has excellent optical and electrical properties, including a high maximum transmittance of 89.1% and a low sheet resistance of 8.0?Ω/sq. When the optimal UVO-treated MoO3/Ag (7.5?nm)/MoO3films are used as the anode in OSCs with the copper phthalocyanine (CuPc)/fullerene (C60) planar heterojunction structure, the OSCs have a power conversion efficiency of 0.55%, which is 2.0 and 1.2 times higher than that of devices with untreated MoO3/Ag (7.5?nm)/MoO3(0.27%) and MoO3/Ag (10?nm)/MoO3electrodes (0.46%), respectively, and competitive with that of indium-tin-oxide-based devices. Because of almost full surface coverage of the Ag interlayer, UVO treatment of MoO3in MAM multilayered electrodes can improve charge carrier injection/extraction at the anode contact and hence improve the photovoltaic performance of OSCs.