Research On The Photoabsorbing Layer FAPbI₃ Of Perovskite Solar Cells Based On First Principles

The problem of energy shortage is becoming more and more serious,and there is an urgent need to develop and utilize renewable energy for the sustainable development of mankind.Solar energy reserves are huge,and solar cells can use solar energy efficiently,so it comes into being.Solar cells have also undergone several generations of development,the first generation is silicon-based solar cells,with high photoelectric conversion efficiency and good stability,but the production cost is too high;The second generation is thin-film solar cells,which have low production costs,but low photoelectric conversion efficiency,and it is difficult to meet practical requirements;The third generation of perovskite solar cells,because of its own high photoelectric conversion efficiency and low production cost and has become the mainstream of recent research,from the advent to the present more than ten years,photoelectric conversion efficiency from the beginning of 3.8%to 25.7%,in the field of new energy has great development potential.However,there are also some problems in the development of perovskite solar cells,that is,it is difficult to maintain their stability,especially humidity stability,while having high photoelectric conversion efficiency.Its light absorbing layer easily reacts with water vapor in the air,resulting in a decrease in the performance of the device.To realize the industrialization of perovskite solar cells,it is necessary to solve the problem of their humidity stability.Doping and modifying the light absorbing layer of perovskite solar cells is an efficient and low-cost solution.In this paper,Cs and Cl were used to co-dope the light absorbing layer FAPb I₃of perovskite solar cells by first-principles method.1、The geometry,electronic structure and optical properties of Cs and Cl-doped FAPb I₃were studied.It was found that the FA_1-xCs_xPb I_3-yCl_ysystem could maintain a stable perovskite structure.With the increase of Cs and Cl incorporation,the band gap of the system becomes larger.The effect of increasing the diffusion at the bottom of the conduction band is stronger than that at the top of the valence band,that is,the effect of reducing the effective mass of the electron of the doped system is more obvious than that of the effective mass of holes,which is conducive to the transport of photogenerated carriers.The optical properties show that the system has a good absorption effect on visible light,but excessive Cl will lead to the degradation of optical performance,and the optical performance is best when x=0.125 and y=0.125.2、The 001 surface of the cubic phase FAPb I₃and the surface after doping Cs and Cl were theoretically simulated at each adsorption site,and the adsorption energy,state density,differential electron density and Mulliken charge distribution of the system were calculated.It was found that water molecules were most easily adsorbed at the T2 site,and the adsorption energy of the doped surface became larger,indicating that the doped surface had an inhibitory effect on water molecules.The orbital state density of Pb atoms and Cl atoms at each adsorption site overlaps with the orbital density of O atoms in water molecules and becomes smaller than that of the eigensurface and is far from the Fermi level,indicating that the possibility of water molecules bonding with the surface decreases.Mulliken charge distribution analysis showed that the number of electron transfers between the doped surface and water molecules decreased,indicating that the role between the surface and water molecules was weakened.These results show that the surface energy after doping Cs and Cl can inhibit the entry of water molecules into the surface to a certain extent.The co-doping of appropriate amounts of Cs and Cl improves the photoelectric conversion efficiency and humidity stability of perovskite solar cells in the above studies,which can provide theoretical guidance for the experimental preparation of more efficient solar cells and further promote the industrialization of solar cells.