Interface Optimization And Defect Passivation Of In Perovskite Solar Cell

In just a few years,the photoelectric conversion efficiency of perovskite-based perovskite solar cells（Perovskite solar cell,PSC）has rapidly increased from 3.8%to 25.5%,so it has attracted much attention.As the core of solar cells,perovskite materials have the advantages of higher absorption coefficient,lower exciton binding energy,longer carrier diffusion length and so on.However,the defect state of perovskite thin films will seriously affect the efficiency and stability of PSC,which is not conducive to the commercialization of PSC.Therefore,it has been a hot topic to reduce the defects of perovskite thin films to restrain carrier recombination.In this paper,interface optimization and defect passivation strategies are used to improve the quality of perovskite thin films,so as to improve the efficiency and long-term stability of battery devices.The main results are as follows:（1）SnO₂ is a commonly used and efficient electron transport layer material,but the lattice mismatch between tin dioxide and perovskite layer leads to interface defects,which leads to carrier recombination and reduces interfacial charge transfer.Therefore,we deposited L-aspartic acid（L-Asp）on the surface of SnO₂ as a bridge between interfaces to transport photogenerated carriers.The results show that the L-Asp buffer layer reduces the fluorescence lifetime of photogenerated carriers at the interface from 42.47 ns to 19.58 ns,and successfully improves the carrier extraction ability of SnO₂ layer to perovskite layer.As a result,the photoelectric efficiency of PSC using L-Asp buffer layer has been improved from 16.89%to 18.46%.（2）The carrier non-radiative recombination is caused by a large number of defects at the grain boundary in the perovskite film.In order to reduce the grain boundaries and passivation defects in the films,sodium glycine（Sodium glycine,SG）,a crosslinking agent,was introduced into perovskite precursors.The results show that the amino and carboxylate groups at both ends of the organic ions of SG can form ionic bonds and coordination bonds with the mismatched Pb²⁺in perovskite to passivate the defects,and can effectively control the nucleation of perovskite so that the grains can grow fully,increase the grain size of perovskite and reduce the grain boundary.At the same time,the densification and crystallinity of perovskite films were improved by connecting adjacent perovskite with amino and carboxylate groups of SG organic ions.In addition,the presence of Na⁺can assist the L-Asp buffer layer to enhance the carrier extraction from the perovskite layer by the SnO2 layer,and reduce the photogenerated carrier lifetime at the interface from 19.58 ns to 13.51 ns.At the same time,Na⁺increases the ion radius of I^-on the grain surface and hinders its migration in the film,which further enhances the passivation effect.As a result,the photoelectric conversion efficiency of PSC increased from 18.46%to 19.61%.（3）Through the optimization of the first two steps,the quality of perovskite thin films is improved,but there is a defect that the interface between perovskite thin films and hole transport layer（Spiro）has not been passivated.Therefore,we deposited a small amount of 2-hydroxyacetophenone（2-Hydroxy acetophenone,2-HA）on the surface of perovskite films.The results show that the carbonyl group and hydroxyl group of 2-HA molecule form coordination bond and hydrogen bond with Pb²⁺and I^-on the surface of the film,which passivates the defects on the surface of the film.The results show that the surface modification of perovskite films with a small amount of 2-HA has no significant effect on the morphology of perovskite films.However,the results of water contact angle test of perovskite films show that the benzene ring of 2-HA hinders the erosion of perovskite films by water to some extent.Therefore,the photoelectric conversion efficiency and long-term stability of PSC have been improved.Finally,after three-step optimization,the efficiency of PSC reached 20.71%,can still maintain the initial efficiency of 80.1%after being placed in air（25℃,RH≈50%）for 100 h.