Preparation And Properties Of Perovskite Solar Cells Based On Surface And Bulk Passivation

Organic-inorganic hybrid perovskite solar cells have attracted extensive attention due to their excellent photoelectric properties and low-cost preparation methods.After more than a decade of development,the highest photoelectric conversion efficiency of perovskite solar cells has reached more than 25%.However,the quality of perovskite films is still one of the limiting factors on device performance of perovskite solar cells.At present,solution deposition method is the most popular perovskite films/devices fabrication technique.The quality evaluation criteria of perovskite films mainly include grain size,density,phase purity and defect density.Early studies on perovskite cells focused on improving grain size,density and phase purity.However,due to the low preparation temperature of perovskite films and the uncontrolled nucleation and growth process,a great number of defects will occur during the crystallization process of perovskite films.In recent years,the research focus of perovskite battery has been partially transferred to the defect passivation of perovskite films,so it is very important to explore the formation mechanism of defects in perovskite films and develop facile defect passivation methods of perovskite films.In this paper,we aim to improve the film quality of perovskite and the device performance of perovskite cells by bulk defect passivation and surface defect passivation.The main research contents and results are as follows:（1）The device performance of perovskite cells was improved by introducing potassium iodide（KI）additives.The effects of introducing KI into two-step lead salt solution on lead halide solution,perovskite conversion,defect density,and cell performance were studied using steady state photoluminescence spectroscopy,UV-Vis near-infrared absorption spectroscopy,X-ray diffraction scanning electron microscopy and volt-ampere characteristic curve measurements.The experimental results show that the introduction of proper amount of KI in lead halide solution is beneficial to the formation of iodine-lead acid complex with high iodine coordination number,which can improve the crystallinity of lead halide film and perovskite film and improve the conversion rate of lead iodide phase to perovskite phase.The defect density in the perovskite film decreased to 7.5×10¹⁵ cm^-3from 8.7×10¹⁵ cm^-3 for the film without KI and the electron mobility increased from 3.69×10^-3 cm² V^-1 s^-1 to 1.15×10^-2cm² V^-1 s^-1.The photoelectric conversion efficiency of the perovskite cells（Au electrode）also increased from17.49%to 19.17%.（2）The surface defects of the perovskite film were reduced by spinning Ethanedithiol（EDT）on the surface of the perovskite film and in situ annealing treatment.The experimental results show that the root mean square roughness of the perovskite film surface decreases from14.08 nm to 11.02 nm,and the grain size of the perovskite film increases from 350 nm to 450nm.The introduction of EDT greatly improved the surface morphology of perovskite films.In addition,the space charge limited current（SCLC）measurements indicate that the defect density of the perovskite film decreased from 1.13×10¹⁶ cm^-2 to 6.6×10¹⁵ cm^-2after EDT modification and accordingly the carrier mobility was also significantly improved.After EDT treatment,the highest photoelectric conversion efficiency of the perovskite solar cells with silver as the back electrode reaches more than 16%.