The Study Of Defect Passivation For Organic-inorganic Hybrid MAPbI₃ Perovskite Solar Cells

Perovskite solar cells（PSCs）have received a great deal of research attention,due to their excellent photoelectric properties,such as long charge carrier lifetime,tunable bandgap,and broad absorption range,etc.The power conversion efficiency（PCE）of PSC devices has increased from 3.8%in 2009 to 25.5%in 2020 in just 10 years,which has shown great commerlization potential and is considered to be one of the promissing new generation of solar cells.However,despite the rapid development of PSCs,their easy decomposition and poor temperature and humidity stability have seriously hindered their commercialization.In the process of perovskite film crystallization,the non-radiative recombination caused by the interface and grain boundary defects is an important reason to reduce the efficiency and stability of the device.Passivation refers to the use of some chemical substances to react with surface components to inactivate their electronic or chemical activities,which is a general way for many semiconductor devices to reduce perovskite defects and improve their photoelectric properties.It is very important to reduce defects by passivation to improve device efficiency and long-term stability.In order to reduce the defects on the upper surface of perovskite,a small molecule passivator,2-mercaptopyrimidine（MPM）,was introduced to passivate the defects on the surface of MAPbI₃ perovskite film.In MPM,the S atom on the sulfhydryl group and the N atom on the pyrimidine ring can coordinate with Pb²⁺,thus passivating excessive PbI₂ and reducing the surface defects of the perovskite film.After passivation,the quality of the crystal film is improved and the defect density is decreased.The PCE of the device was increased from17.85%for the control devices to 19.71%with MPM passivation.Moreover,MPM-passivated PSCs also possess superior humidity stability,retaining 94%and 82%of the initial PCEs after720 and 480 h aging in air with a relative humidity of 30%and 60%,respectively.For the defects on the lower surface of perovskite,we introduced a common amino acid,L-Cys,to modify the surface of TiO₂,so as to make the growth of perovskite more favorable later.L-Cys molecules are anchored to TiO₂ by the coordination of carboxyl group.Nitrogen and sulfur atoms in the amino and sulfhydryl groups can be coordination passivated with excess Pb²⁺.The modified electron transport layer is more closely bound with the perovskite layer,which enhances the charge transfer.The crystal film grown on the surface of the modified TiO₂presents higher quality,and the PSC devices prepared based on the modified TiO₂ also show higher photoelectric performance.Compared with the unmodified device（PCE of 17.34%）,the modified devices show a higher PCE of 18.98%.In this paper,we provide a strategy to improve the efficiency and stability of MAPbI₃ perovskite solar cells by using simple small molecules in terms of passivation and surface modification.