Dopant Control of Electron-Hole Recombination in Cesium-Titanium Halide Double Perovskite by Time Domain Ab Initio...

Using nonadiabatic (NA) molecular dynamics combined with time domain density functional theory, we simulate electron-hole recombination in pristine and doped inorganic Pb-free double perovskite Cs₂TiBr₆. We show that replacing the titanium and/or bromine with silicon and/or chlorine extends the charge carrier lifetime. Importantly, dopants avoid deep traps despite the fact that they do not change the fundamental band gap of Cs₂TiBr₆, and they decrease the NA electron-phonon coupling and accelerate decoherence arising from the reduced overlap of electron and hole wave functions as well as fast phonon modes induced by light dopants, respectively, suppressing electron-hole recombination. More importantly, codoping can reduce the formation energy of silicon and achieve higher doping concentration, potentially increasing the lifetime further. Our study suggests a rational strategy to reduce energy losses by codoping in design of high-performance all-inorganic Pb-free perovskite solar cells.