Weak temperature-dependent hole injection and electron–hole recombination at the CH3NH3PbI3/NiO heterojunction: a time-domain ab initio study

Abstract

Inorganic hole transport material (HTM) NiO is superior to traditional organic HTMs due to its high stability and conductivity. Efficient charge separation and slow charge recombination are two key important steps in determining the efficiency of solar cells but they often show strong temperature dependence. Using nonadiabatic molecular dynamics combined with ab initio time-domain density functional theory, we have demonstrated that the time scales for both hole transfer and electron–hole recombination show weak temperature dependence in MAPbI₃/NiO perovskite solar cells. The hole transfer occurs on sub-100 fs at both high and low temperatures. Hole transfer proceeds slightly faster at high temperature than low temperature due to enhanced NA coupling. Notably, the hole remains hot over 200 fs energy relaxation before cooling to interact with the remaining electrons, form excitons and accelerate electron–hole recombination, providing an excellent advantage for solar energy applications. Following charge separation, the electron–hole recombination takes place in several nanoseconds at both low and high temperatures. The acceleration only by a factor of below 2 arises because increased atomic motions cause rapid loss of coherence, which competes successfully with the enhanced NA coupling. The detailed atomistic understanding of the reported results allows us to generalize the conclusions to other hole transport materials and suggests weak temperature-dependent charge dynamics properties enabling the high performance of perovskite solar cells.