Achieving Enhanced Visible-Near-Infrared Light Absorption in Stable Lead-Free Vanadium-Based Perovskite Nanocrystals via Structural Regulation.

Lead-free halide perovskites are promising materials for solar energy applications. However, their efficiency is hindered by poor light absorption in the visible-near-infrared region. Herein, we introduce vanadium (V) with low-lying ground/excited-state energy levels to form two types of stable lead-free V-based perovskite (Cs 2 NaVCl 6 and Cs 3 V 2 Cl 9 ) colloidal nanocrystals (NCs) with strong light absorption covering the ultraviolet to near-infrared region. We find the absorption can be further enhanced by structural regulation, in which the zero-dimensional (0D) Cs 3 V 2 Cl 9 NCs show stronger and red-shifted (up to 1400 nm) light absorption compared to the three-dimensional Cs 2 NaVCl 6 NCs. In 0D Cs 3 V 2 Cl 9 NCs, [V 2 Cl 9 ] 3- dimers play a vital role in governing strong visible-near-infrared light absorption. We demonstrated their application for photocatalytic CO 2 reduction. Our work sheds light on the structure-property relationship governing the absorption behavior, providing a novel route for tuning the light absorption ability of lead-free halide perovskites.