Low-temperature preparation of titanium dioxide thin layer for highly efficient CsPbI3 perovskite solar cells

All-inorganic CsPbI3 perovskite solar cells (PSCs) are the focus of the photovoltaic field due to their great thermal stability and potential in tandem devices. However, the common titanium dioxide (TiO2) electron transport layer (ETL) is manufactured at high temperature and is challenging to regulate the thickness. Here, we propose a unique strategy to fabricate thin TiO2 at low temperatures using atomic layer deposition (ALD) and a low-concentration Titanium tetrachloride/isopropanol (TiCl4/IPA) solution method. The ultra-thin compact ALD-TiO2 (A-TiO2) is employed to minimize the leakage channels and suppress the recombination rate at the tips of rough fluorine-doped tin oxide (FTO) substrates. Subsequently, the solution-TiO2 (S–TiO2) regulates the work function to improve the energy level alignment. The A-TiO2/S–TiO2 composite facilitates carrier charge extraction and transport at the interface between ETL and perovskite layer. As a result, the device-based A-TiO2/S–TiO2 ETL delivers a champion efficiency of 19.6% and outstanding stability under continuous illumination in ambient air. This study demonstrates a simple and cost-effective method for fabricating CsPbI3 PSC and promoting their potential for commercialization.