Organic heterojunctions of phthalocyanine-reduced graphene oxide above percolation threshold for photovoltaic application

Abstract

In this article, non-fullerene, cost effective, and highly soluble zinc tetra-tert-butyl phthalocyanine-reduced graphene oxide (ZnTTBPc-RGO) heterojunction have been used as an active layer in organic photovoltaic devices. The RGO content in the active material is varied from 0.25–0.5 volume fractions which are above the percolation threshold of 0.167 volume fraction of RGO. Temperature dependent current density–voltage characteristics show a transition from Ohmic conduction to space charge limited current (SCLC) conduction at higher applied bias voltages (≥1 V). This enables us to extract charge carrier mobility values of the heterojunction at different temperatures using a trap-free SCLC model. A donor–acceptor solution processable photovoltaic device with 0.33 vol.% RGO content of active layer show the highest power conversion efficiency of 1.02%, highest recombination resistance of 48.65 kΩ, and maximum carrier mobility of 4.32 × 10−4 cm2V−1s−1 among the three devices studied. 80 h exposure to ambient conditions see a ∼40% decay of power conversion efficiency. Quantitative analysis on the density of trap states indicates that the best power conversion efficiency and the highest charge carrier mobility correlate well with a minimum of the trap density and a maximum of recombination resistance for these devices.