Surface Modification And Photoelectric Properties Of MAPbI3 Perovskite Single Crystal Wafers

In recent years,a new generation of semiconductor perovskite materials has gradually become the focus of research because of its high absorption coefficient,long carrier diffusion length,simple preparation process,flexible preparation and other advantages.In just over a decade of development,the laboratory efficiency of solar cells fabricated using perovskite materials as light absorbing layers has reached 25.7%,and has developed rapidly.Similar to commercial Si cells,perovskite solar cells can also be divided into polycrystalline and single crystal devices.At present,perovskite polycrystalline thin film devices are the most likely to be commercialized.However,there are many grain boundaries in perovskite polycrystalline thin film and the defect density is high,which has become a stumbling block for its further development.However,perovskite single crystal has no grain boundary,and its defect density is far lower than that of polycrystalline,which can be comparable with monocrystalline silicon.In theory,it can achieve higher efficiency and better stability.However,perovskite single crystal film,like all film materials,has a large specific surface area,so the surface of perovskite single crystal film becomes particularly important in the application of solar cells.The defects on the surface will become the recombination center of carriers,which will seriously affect the performance of solar cells.In addition,because perovskite materials are very sensitive to environmental conditions(temperature,humidity,oxygen),the stability of perovskite single crystal solar cells also needs to be solved.In this paper,the MAPbI3 perovskite single crystal film with micron thickness was grown by the space limited method,and the interaction between two surface passivators and the surface of single crystal film was studied by Lewis acid-base theory.The interface modification improves the surface condition of the single crystal wafer,promotes the carrier transmission at the device interface,and effectively improves the performance and air stability of MAPbI3 single crystal solar cells.(1)The interaction mechanism of PEAI molecular layer on the surface of MAPbI3 single wafer was studied.The coordination between Lewis acid and base pairs reduces the dangling bonds on the crystal surface,reduces the defect density of the single crystal film,and promotes the extraction and collection of carriers at the perovskite/C60 interface of the perovskite single crystal device.The device efficiency of MAPbI3 single crystal solar cell can be increased from 19.71%to 21.2%.At the same time,the introduction of PEAI molecular layer also increased the contact angle of the surface of the single crystal wafer to a certain extent,and the hydrophobic ability was enhanced,which made the single crystal device still maintain 80%of the initial efficiency after being stored in normal temperature and humidity air for 750 hours,while the pristine battery without PEAI decreased to 50%of the initial efficiency due to the hydrolysis of MAPbI3.(2)The surface passivation strategy of the bifunctional molecule 3-mercaptopropyl(dimethoxy)methylsilane(MDMS)was proposed.The S atom in the MDMS molecule can coordinate with the exposed Pb2+ion on the surface of MAPbI3 single crystal,reducing the nonradiative recombination of photogenerated carriers.Thereby further improving the efficiency of MAPbI3 single crystal solar cells to 22.2%.At the same time,the introduction of MDMS inhibits the ion migration on the crystal surface,which makes the single crystal device show higher reverse bias stability.In addition,MDMS molecules can polymerize and cross-link on the surface of MAPbI3 single crystal wafer to form a superhydrophobic protective layer.The contact angle of the surface is further increased,which reduces the generation of MAPbI3 hydrolysate,further improving the air storage stability of MAPbI3 single crystal solar cell devices,and can still maintain 90%of its initial efficiency when stored in air for 950 h.This paper provides an effective way for surface modification of perovskite single crystals,which is important for improving performance of single-crystal perovskite solar cells,photodetectors,X-ray detectors,etc.