Atomically Altered Hematite for Highly Efficient Perovskite Tandem Water-Splitting Devices

Photoelectrochemical (PEC) cells are attractive for storing solar energy in chemical bonds through cleaving of water into oxygen and hydrogen. Although hematite (alpha-Fe2O3) is a promising photoanode material owing to its chemical stability, suitable band gap, low cost, and environmental friendliness, its performance is limited by short carrier lifetimes, poor conductivity, and sluggish kinetics leading to low (solar-to-hydrogen) STH efficiency. Herein, we combine solution-based hydrothermal growth and a post-growth surface exposure through atomic layer deposition (ALD) to show a dramatic enhancement of the efficiency for water photolysis. These modified photoanodes show a high photocurrent of 3.12 mAcm(-2) at 1.23V versus RHE, (> 5 times higher than Fe2O3) and a plateau photocurrent of 4.5 mAcm(-2) at 1.5 V versus RHE. We demonstrate that these photoanodes in tandem with a CH3NH3PbI3 perovskite solar cell achieves overall unassisted water splitting with an STH conversion efficiency of 3.4%, constituting a new benchmark for hematite-based tandem systems.