Ambient processed and stable all-inorganic lead halide perovskite solar cells with efficiencies nearing 20% using a spray coated Zn1−xCsxO electron transport layer

Achieving ambient-processed and stable all-inorganic halide perovskite solar cells with high conversion efficiencies is a well-established goal within the halide perovskite research community. In striving for this, electron transporting layers based on common TiO2 and SnO2 nanoparticles have been widely deployed, however, can stifle device performance due to their requirement for high temperature processing and non-uniform layer deposition. Using a low-temperature processed Cs-doped ZnO nanocrystalline electron transport layer and a narrow-bandgap (~1.70 eV) all-inorganic absorber (Cd-doped CsPbI2.5Br0.5), we report ambient-processed solar cells which exhibit high conversion efficiencies (>19.75%) and stable performance under ambient condition (>300 h). A smooth interface is established by combining spray-deposition of the electron transport layer and injection of hot-air during the perovskite deposition, which crystallizes smooth, compact perovskite thin films directly from solution. The high performance is attributed to preserving a solar-friendly and phase-stable perovskite layer, along with improved charge carrier management.