Alkali Metal Chloride-Doped Water-Based TiO 2 for Efficient and Stable Planar Perovskite Photovoltaics Exceeding 23% Efficiency.

TiO 2 is one of the most broadly employed electron transport materials in n-i-p structure perovskite solar cells (PSCs). Low-temperature non-hydrolyzed sol-gel method is developed to prepare TiO 2 in order to simplify the fabrication process and match with the planar structure PSCs. Conventional low-temperature TiO 2 film using organic solvents as dispersants makes direct doping challenging due to limited solubility. Here, a newly developed water-based TiO 2 solution is directly doped with different alkali chlorides, resulting in better conductivity, compatible energy level matching, and enhanced charge extraction in terms of electron transport layer (ETL) for PSCs. As a result, a power conversion efficiency of 23.15% is achieved based on NaCl-doped TiO 2 with competitive storage stability and light stability. The water-based TiO 2 ETL for more general doping of various solutes opens up a new avenue for environmental-friendly manufacturing superior ETL toward high-efficiency and stable perovskite photovoltaic devices.