Tuning the Excited-State Dynamics of CuI Films with Electrochemical Bias

Owing to its high hole conductivity and ease of preparation, CuI was among the first inorganic hole-transporting materials that were introduced early on in metal halide perovskite solar cells, but its full potential as a semiconductor material is still to be realized. We have now performed ultrafast spectroelectrochemical experiments on ITO/CuI electrodes to show the effect of applied bias on the excited-state dynamics in CuI. Under operating conditions, the recombination of excitons is dependent on the applied bias, and it can be accelerated by decreasing the potential from +0.6 to -0.1 V vs Ag/AgCl. Prebiasing experiments show the persistent and reversible "memory" effect of electrochemical bias on charge carrier lifetimes. The excitation of CuI in a CuI/CsPbBr₃ film provides synergy between both CuI and CsPbBr₃ in dictating the charge separation and recombination.