Study Of Charge Dynamics And Device Stability In Perovskite Solar Cells

Recently,new thin-film photovoltaic devices named perovskite solar cells have attracted wide attention for increasing photoelectric conversion efficiency.Since the appearance of the perovskite solar cells in 2009,the photoelectric conversion efficiency of the cell has been increased from 3.8% up to 22.7%,which is comparable to silicon solar cells,so that the efficiency is not the rate-limiting step for industrial application.The focus has been transferred to fabricate large-area,high stability and eco-friendly photovoltaic devices,especially the problems in stability have become the biggest challenge in this area.Meanwhile,many researchers have been trying to study the stability problems of materials or charge transformation from dynamics.These works can help to find the micro-mechanisms hiding behind the macro-phenomena,and also to direct the experiments to improve device stability.Therefore,we paid efforts on clarifying the mechanisms of charge accumulation and recombination,after that the connection between these mechanisms and the device stability has also been established.Besides,we also put forward some advice for improving device stability.The typical research achievements are summarized as following:(1)Photocharge accumulation in perovskite solar cells has been systematically investigated by electrochemical spectroscopy and transient photocurrent/photovoltage(TPC/TPV)methods.It is found that the non-equilibrium photocharges are stored in the selective charge transport layers.(2)Combining the results of photocharge accumulation,an ultrathin interface defects passivation layer has been introduced to study the charge recombination in perovskite solar cells.It is found that the non-equilibrium photocharges stored in the selective charge transport layers follow a backward recombination mechanism.That is,the photocharges are firstly captured by the interface defects corresponding to the fast photovoltage decay,while the bulk charge recombination instead of the diffusion process dominates the slow photovoltage decay process.(3)Combining the mechanisms of photocharge accumulation and recombination in perovskite solar cells,the mechanisms of device performance degradation under continuous light and bias voltage have been studied.It is found the increasing of interface defects is the prime reason for device performance degradation.On the one hand,these interface defects can easily capture the non-equilibrium photocharges stored in the selective charge transport layers resulting in a lower charge collection efficiency.One the other hand,the current caused by defects capture has an opposite transport direction compared with photocurrent,which can improve the dark current and decrease open circuit voltage and fill factor.This result can confirm the importance of the interface engineering to enhance the device stability.