Solution-processed indium oxide electron transporting layers for high-performance and photo-stable perovskite and organic solar cells

Abstract

Interface engineering is considered the key to improving the device performance and stability of solar cells. In particular, TiO₂ nanostructures, when used as electron transporting layers (ETLs) in metal halide perovskite solar cells (PSCs), led to excellent power conversion efficiencies (PCEs) of over 20%. They effectively transferred charge carriers from the perovskite and suppressed charge recombination at the interfaces. However, the photocatalytic effect of TiO₂ on the perovskite can significantly degrade the device performance under ultraviolet illumination. Therefore, other classes of n-type metal oxides with a wide band gap should be developed to improve their photo-stability. Herein, we demonstrate the development of In₂O₃ thin films by a solution process and their application as ETLs in PSCs and organic solar cells (OSCs). Pin hole-free In₂O₃ ETLs obtained by the thermal decomposition of an In precursor thin film exhibit high conductivity (2.49 × 10⁻⁴ S cm⁻¹) and low surface roughness (7.33 nm). This leads to impressive PCEs of 14.63% and 3.03% for the PSC and the inverted OSC, respectively. Furthermore, the In₂O₃-PSC shows better photo-stability than the TiO₂-PSC by virtue of the wider band gap of In₂O₃, which leads to a PCE retention of 74% and 46%, relative to the initial PCE values of the PSC and the inverted OSC, respectively.