The Study On Stability Of The Perovskite Solar Cells

The organic-inorganic hybrid perovskite solar cell is a rising star in the field of photovoltaic devices.It emerged as a highly attractive sunlight harvesting materials for their high absorption coefficient,high charge carrier mobility and long electron-and hole-diffusion lengths,together with their moderate cost and low temperature solution-process ability.In just 10 years,it has drawn intense attention in the field of thin-film photovoltaics,and power conversion efficiency?PCE?of perovskite solar cells?PSCs?has surprisingly skyrocketed from 3.8%to 22.7%.However,the long-term operational stability with exposure to prolonged humidity,heat,light,and oxygen is the bottleneck restraction for the commercial application of PSCs.The control of the perovskite chemical composition and the optimization of the crystallization process are important ways to improve the stability of the perovskite solar cell.On the basis of methylamine?CH₃NH₂?induced defect-healing process,a liquid-state precursor phase?MAPb I₃·MACl·xCH₃NH₂?was discovered by changing the chemical composition of the precursor solution.It converted to metastable MAPb I₃·MACl upon stepwise release of volatile CH₃NH₂ at the room temperature owing to the weak hydrogen bonding,and then the crystallization process of MAPbI₃was changed owing to the volatile of MACl during the annealing.High-quality perovskite films with a grain size of 3-5?m and lower grain boundary density were prepared.According to reports,the grain boundary is the main channel for water-intercalation of perovskite films causing the perovskite crystal structure to collapse.The stability of perrovskite materials in high humidity environments increased with the decrease of the grain boundary density.The photoelectric conversion efficiency still maintained 85%of the initial value after 350 hours stored in a 40%relatively humidity room temperature environment.In addition,methylamine?CH₃NH₂?induced defect-healing process enhances the orientation of the perovskite material,and only vertical grain boundaries exist.Therefore,the device efficiency achieved 17%via this process.The discovery of this metastable mesophase has provided new directions for the improvement and development of gas process.Apart from the above-mentioned improvement in the preparation process,the control of the chemical composition of the perovskite material is the fundamental method for improving the stability.Firstly,methylamine chloride?MACl?was introduced to the precursor solution accoding to stoichiometric ratio.The crystallization process of perovskite slowed down under the property of the relatively low formation energy of methylamine lead chloride,to obtain high quality and coverage of perovskite films.The photoelectric conversion efficiency of the devices has increased to 17.5%.Secondly,ion exchange/thermal decomposition technology was exploited,and a PbI₂-excess\Cl-doped perovskite film was prepared at elevated temperature,in which the I-Cl exchange and MACl sublimation occurred simultaneously.This combined strategy could guarantee that as much chlorine as possible was doped into the perovskite crystal lattice,which reduced defect density of the perovskite films obviously and enhanced carrier diffusion length.In short,long-term stability of perovskite solar device was realized in ambient air condition without device encapsulation,and the power conversion efficiency of the device is boosted from 17.17%to 20.15%..