Stability Optimization Of CH₃NH₃PbI₃ Perovskite And Application Of Solar Cells

Organic–inorganic halide perovskite solar cells（PSCs）have drawn enormous attention in recent years with power conversion efficiencies（PCE）rushing from 3.8%to a certified 23.3%.Superb properties such as adjustable band gap,strong absorption and long carrier diffusion lengths make perovskite materials attractive for optoelectronic devices.Compared to ordinary semiconductors,perovskite has many advantages:natural abundance,low-cost raw materials and solution-based fabrication routes,providing an abroad prospect for the next generation of photovoltaics.Accompanied with the improvement of PCE,the stability of perovskite has become a focus recently.Thermal instability of hybrid perovskite thin films is one of the important issues that must be overcome on the way to commercialization of perovskite solar cells.This paper investigates the effect of grain size and grain boundaries（GBs）on the thermal degradation behavior of CH₃NH₃PbI₃（MAPbI₃）thin films and analysis the degradation mechanism.PSCs based on different grain size of MAPbI₃ films are prepared,the effects of grain size and GBs on the electrical properties of the PSCs are discussed in detail.The main work of this paper is as follows:（1）MAPbI₃ films are prepared by anti-solvent one-step deposition method and perovskite is successfully controlled by using different annealing processes,including thermal annealing（TA）and solvent annealing（SA）.Scanning electron microscope（SEM）,X-ray diffraction（XRD）and ultraviolet-visible absorption spectra（UV-vis）are utilized to compare the characteristics of MAPbI₃ films prepared by different annealing processes.MAPbI₃ thin films prepared by TA process show larger grain size and better thermal stability.（2）The PSCs based on traditional mesoporous structure are prepared.The PSCs based on MAPbI₃ films prepared by SA and TA process respectively yield PCE of 18.56%and 16.87%.According to the J-V curves,EQE curves,hysteresis curves,it is demonstrated that the larger grain size not only improves stability,but also enhances the photovoltaic performance of PSCs.（3）The degradation mechanisms of perovskite thin films caused by GBs are summarized according to the combination of the atomic model of GBs and related theoretical research.Carrier recombination of perovskite solar cells is characterized,including dark current,ideal factor and electrochemical impedance spectroscopy,which confirms the inhibition of large grain on carrier recombination.