Surface-modified ultra-thin indium zinc oxide films with tunable work function for efficient hole transport in flexible indoor organic photovoltaics

The stability of the electrical and optical properties of electrodes subjected to physical strain need to be ensured to enhance the performance of indoor organic photovoltaics (OPVs). In this study, we demonstrate the stable performances of flexible OPVs by producing an ultra-thin (20 nm) indium zinc oxide (IZO) electrode by co-depositing its surface with Ni metal, which improves the electrical conductivity and energy-level alignment owing to a hole-transport layer. As an anode, the resulting ultra-thin IZO electrode exhibits a relative sheet resistance of 250 Ω sq⁻¹, high transmittance of 91.5% at 450 nm, and high work function of 5.05 eV. More importantly, the proposed electrode shows an enhanced bending performance, which is attributable to its amorphous structure formed as a result of co-deposition. Therefore, flexible OPVs with the proposed electrode show much higher performances (42% power conversion efficiency under indoor illumination) than those with a reference IZO anode. Furthermore, they exhibit outstanding flexural endurance properties while maintaining 84% of their original power conversion efficiency after 1500 cycles of bending at a bending radius of 8.1–4.2 mm on polyimide substrates. This study demonstrates an effective strategy for improving the performance of optoelectronic devices requiring electrical and mechanical stability.