Defect-passivation Of Perovskite Via The Addition Of Metformin For Application In High-performance Perovskite Solar Cells

Perovskite solar cells have attracted the attention of researchers due to their easy fabrication and excellent optoelectronic properties.Compared with their n-i-p cousins,perovskite solar cells with p-i-n structure have better stability,longer operational lifetime,and are easier to use in tandem cells.But their efficiency has been lagging behind that of perovskite solar cells with an n-i-p structure.It is generally believed that nonradiative recombination losses due to defects account for the difference.Here in,we systematically study the defect passivation effect of metformin hydrochloride(MetHCl)additive on perovskite materials and its application in p-i-n structure perovskite solar cells.A strategy to reduce nonradiative recombination in perovskite solar cells is proposed.The specific research contents are as follows:1.MetHCl was used as an additive in the ground bottom precursor(GBP)PbI2.The multifunctional group of metformin hydrochloride can interact with PbI2 in the precursor solution,retard the crystallization of perovskite,and effectively regulate the crystal growth of perovskite.Thus,the pinholes of the perovskite films are reduced,and a high quality perovskite film with lower defect density and denser grain is obtained.It can be seen from the morphology that the non-volatile MetHCl can remain in the perovskite film to passivate the grain boundaries,while doping with a high concentration of MetHCl will produce a low-dimensional structure at the grain boundaries of the film,which can effectively inhibit the non-radiative recombination at the grain boundaries.After fabricating the corresponding p-i-n MAPbI3-xClx device,an open circuit voltage of 1.16 V was obtained and the power conversion efficiency(PCE)of the device was increased from 19.71%to over 21%.2.MetHCl was used as an additive in the top surface precursor(TSP)MAI:MetHCl in MAI has little effect on the morphology and structure of perovskite,and no excess salt or low-dimensional structure remains on the surface of perovskite.Although it is not directly added to PbI2,it can still interact with PbI2 during the dynamic spin coating process to modify the surface environment of the obtained perovskite film.The p-i-n perovskite solar cells were fabricated based on the films with MetHCl in top surface precursor,and a highest PCE of 21.28%can be obtained.Finally,we added MetHCl to the two precursors of perovskite thin films at the same time for the preparation of perovskite solar cells,and a champion PCE of 21.89%was obtained.Concurrently,the stability of the device is also greatly improved.The PCE of the unpackaged device can still retain 80%of the initial efficiency after 800 hours at room temperature in an atmospheric environment with a humidity of 10%to 30%.