The Study Of Photovoltaic Processes Of Perovskite Solar Cells Based On CH₃NH₃PbI₃?Cl?

In recent years,organic-inorganic halide perovskite materials have attracted tremendous research interest due to the excellent photovoltaic conversion efficiency.Recently,For the Perovskite solarcells,many significant progresses have been made in optimizing the composition of perovskite material,device engineering,improving the power conversion efficiency and stability.However,the studies focus on the underlying physical properties of photoexcited states and the separation and recombination processes in perovskite materials are still insufficient.There are only a handful of studies focus on the internal photovoltaic processes under devices working condition in perovskite solar cell.This thesis is based on inverted planar heterojunction perovskite solar cells.We use the experiment tools including magnetic field effect of photocurrent,steady-state and time-resolved photoluminescence spectroscopy,transient photocurrent,light-induced dielectric responses,atomic force microscopy,and scanning electron microscopy to investigate the effects of spin configuration of photoexcited states?defect states?charge carrier transport mobility and charge carrier accumulation at the electrode interface on the photovoltaic process in perovskite solar cells.The research results are as follows:(1)We tune the concentration and depth of trap states in the perovskite film by adjusting the thermal annealing temperature of the perovskite film,and find that the amplitude and sign of the magnetic field effect of photocurrent of the perovskite solar cell device can be changed.By comprehensively analyzing the relationship between the magnitude and sign of the magnetic field effect of photocurrent and the the concentration and depth of the trap states in the perovskite film,we reveal that the interaction of triplet states and the shallow trap states can de-trapping the trapped charge carrier,and contribute to photocurrent.The interaction of triplet states and the shallow trap states is an useful photovoltaic process;While triplet states react with deep trap states,the deep trap states help triplet release energy,and generate non-radiative recombination,which is a non-useful photovoltaic process.(2)Doping the electron transport layer of perovskite solar cell with N-DMBI can improve the photovoltaic conversion efficiency of the device.Comparing the undoped device and the optimal doped device(0.02 wt%N-DMBI doped),the power conversion efficiency is enhanced from 13.83%to 15.36%.The short-circuit current improved significantly from 19.08 mA/cm~2 to 22.79 mA/cm~2,while the open circuit voltage and fill factor decreased with increasing doping concentration.The study shows that N-DMBI doping can significantly improve the conductivity and electron transport ability of PCBM film;And we find that while increasing doping concentration of N-DMBI,the charge accumulation at the electrode interface of device increasing gradually,and the built-in electric field of the devices is also weakened by the charge accumulation at the electrode interface.These results reveal the reason why the open circuit voltage and fill factor dropped while increasing the N-DMBI doping concentration.The AFM morphology study of PCBM film shows that N-DMBI doping has an adverse effect on the surface morphology of PCBM film,which adversely affects the charge collection at the electrode interface.And revealing the reason why N-DMBI doping induce the increasing of charge accumulation at the electrode interface.(3)The light illumination during the two-step spin coating processes of the perovskite film can improve the power conversion efficiencies of the finally prepared perovskite solar cell devices.As the light intensity increased from 0 mW/cm~2 to 80 mW/cm~2 during spin coating,the efficiency gradually increased from 15.22%to 18.16%.Our find that spin coating the perovskite film under illumination can effectively reduce the trap density of the perovskite film,and increase the builted-in electric field,and reduce the charge accumulation in the device,and improve the charge carrier transport mobility and collection efficiency and finally enhance the open circuit voltage,short-circuit current and fill factor of the perovskite solar cell devices.Moreover,spin coating the perovskite film under illumination can effectively inhibit the non-radiative recombination in the perovskite film,and prolong the lifetime the average diffusion length of the charge carriers in the perovskite film.