Large Carrier-Capture Rate Of Pb-I Antisite In Ch3nh3pbi3 Induced By Heavy Atoms And Soft Phonon Modes

The Pb-I antisite was reported to be a possible deep-level recombination-center defect in CH3NH3PbI3 solar cells with a concentration higher than 10(15) cm(-3) under I-poor conditions. However, whether it is really an effective nonradiative recombination center and limits the photovoltaic efficiency depends also on its cross sections for capturing the electron or hole carriers, which is difficult to determine in both experiment and theory. Here we use a recently developed method to overcome the high computational cost of electron-phonon coupling calculation and implement it in the standard first-principles code QUANTUM ESPRESSO so that we can calculate the carrier-capture cross sections effectively for the point defects in complicated semiconductors, such as CH3NH3PbI3. The calculation showed that both the hole-and the electron-capture cross sections and capture rates of PbI are large relative to those of the point defects in conventional semiconductors, such as Si or GaP, which is attributed mainly to the heavy Pb-I atoms and the soft phonon modes in this Pb halide. Nonradiative recombination increases the thermal energy by exciting the phonons in the soft Pb-I lattice, whereas the contribution of the organic CH3NH3 group is negligible. Since PbI has a higher concentration under I-poor conditions, especially when the semiconductor is p-type, our results suggest that the minority-carrier lifetime and thus the photovoltaic efficiency should be very limited in p-type CH3NH3PbI3 and p-type doping should be avoided for fabricating high-efficiency CH3NH3PbI3 solar cells under I-poor conditions. Similar calculations can be used for studying the influence of various defects on the photovoltaic performance of other organic-inorganic hybrid and inorganic halide perovskites, shedding light on the design of high-efficiency solar cells.