Elucidating the Impact of Charge Selective Contact in Halide Perovskite Through Impedance Spectroscopy

The electron and hole selective contact (SC) play a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC was elucidated, by means of impedance spectroscopy. The specific role played by TiO₂ and Spiro-OMeTAD as electron and hole SC in perovskite solar cells was investigated at short circuit condition at different temperatures. We have probed MAPbI₃ and (FAPbI₃)_0.85(MAPbBr₃)_0.15 and elucidated parameters such as charge carrier mobility, recombination resistance, time constant and charge carrier kinetics in perovskite layer and at the interface of perovskite/SC. Charge carrier mobility in mixed perovskite was found to be nearly two order of magnitude higher as compared to MAPbI₃. Moreover, the carrier mobility in devices with only electron SC was found to be higher as compared only hole SC. The charge accumulation at TiO₂/perovskite/Spiro-OMeTAD interfaces were studied via frequency dependent capacitance, revealing higher charge accumulation at perovskite/Spiro-OMeTAD than at TiO₂/perovskite interface. By performing varying temperature frequency dependent capacitance measurements the distribution of density of state within the bandgap of the perovskites, the emission rate of electrons from the trap states and traps activation energy was determined.