Aqueous solution processed tetrasulphonated copper phthalocyanine (TS-CuPc):MoO3 as an efficient hole transporting layer in organic solar cells

Abstract

An environment-friendly hole-transporting interfacial layer for organic solar cells is introduced with aqueous solution-processed MoO3 and Copper phthalocyanine-3,4ʹ,4ʺ,4‴-tetra-sulfonated acid tetrasodium salt (TS-CuPc). Power conversion efficiencies of organic solar cells greatly improved when the hole transporting layer, MoO3 was modified by mixing with TS-CuPc at an optimum ratio. The enhanced performance is explained using atomic force microscopy, impedance spectroscopy, cyclic voltammetry, contact angle measurements, and UV–Vis absorption spectroscopy. Impedance spectra of devices were fitted to an electric circuit model to analyze the influence of buffer layers on the charge transport in the devices. The improved efficiency of optimized device is traced to the lower series and charge transport resistances, lesser recombination, and higher lifetime of mobile charge carriers caused by the minute concentrations of TS-CuPc in the hole transport layer. Furthermore, the incorporation of TS-CuPc in MoO3 was found to enable uniform film growth which leads to higher performance of solar cells.