Application Of Atomic Force Microscope In Perovskite Solar Cells

The organic-inorganic hybrid halide perovskite has excellent photoelectric properties,and the solar cell power conversion efficiency based on perovskite material has exceeded 23%,and has become one of the most promising light absorbing layer materials in the next generation photovoltaic technology.Heterojunctions in photovoltaic devices have a significant impact on carrier separation and transport in cells.In perovskite photovoltaic cells,the generation and separation behavior of photogenerated free carriers are closely related to the heterojunction.There is an urgent need for an effective method to establish the relationship between charge transfer behavior and photovoltaic properties in the perovskite absorber layer.In addition,the current hysteresis effect is common in perovskite solar cells,which seriously affects the output of stable power of the cells.Ion migration is one of the main factors contributing to this phenomenon.Establish the migration path of ion motion in perovskite materials on the micro level and looking for ways to suppress ion migration is the main way to develop stable power output photovoltaic devices.In this paper,the relationship between carrier charge transfer behavior and macroscopic photovoltaic performance in a microscopic perovskite light absorbing layer was established by means of Kelvin probe force microscopy and conductive atomic force microscopy.Using conductive atomic force microscopy and Kelvin probe force microscopy microscopic measurement technology,it is determined that the current of the perovskite grain boundary dominates the current hysteresis behavior in the macroscopic battery.The research content of this article mainly includes the following three aspects:1.The effect of fullerene derivative PCBM-doped perovskite system on the macro-current hysteresis of the cell was studied.By constructing photovoltaic device doped with or without fullerene derivative PCBM,for the purposes of discussion,we define the hysteresis factor(HI)using HI=(PCE_R-PCE_F)/PCE_R.The hysteresis factor of the device before and after doping was reduced from 31.2 to 13.1,it was found that the current hysteresis behavior of the fullerene derivative PCBM doped device was greatly reduced.The position and distribution of PCBM in the perovskite layer were determined by conductive atomic force microscopy and Kelvin probe force microscopy.It was found that the hysteresis behavior of the local grain boundary current signal is the real cause of the unstable power output of macroscopic photovoltaic devices.Transient and steady-state current tests of microscopic grain boundaries and grains show that the doped PCBM is located at the grain boundary to effectively suppress the grain boundary current hysteresis.2.The relationship between charge transfer behavior and macroscopic photovoltaic properties in perovskite films at nanoscale was investigated.Three kinds of heterojunctions based on perovskite film were constructed,and the current value and surface potential difference of the local perovskite film were obtained by atomic force microscope testing techniques.It is found that the surface potential difference and the positive and negative polarity of the perovskite film can be used to analyze the carrier transfer behavior of the perovskite/contact layer heterojunction interface.The magnitude of the potential difference is related to the amount of carrier transfer,The polarity is related to the type of charge carrier(hole or electron)transfer.In addition,by comparing the surface potential and current value of perovskite film in dark and in light,it is found that the role of the perovskite in these heterojunctions depends on the nature of the contact layer.3.The effects of the absorbing layer thickness and intensity of the light on the separation and transmission of photogenerated carriers were investigated.The thickness of the perovskite film was adjusted by attempting to change the concentration of the perovskite precursor,and it was found that the difference between the surface potential values and the surface average current increased as the thickness of the perovskite film increased.By changing the intensity of different illumination,it is found that the values of surface potential and photocurrent become larger as the light intensity increases,indicating the excellent photoelectric properties of the perovskite films.