Epitaxial Growth And Band Gap Control Of CsPbX₃ Thin Films On Typical Single Crystal Substrates

In 2009,Japanese scientist Miyasak innovatively used organo-inorganic hybrid titanite materials CH₃NH₃Pb I₃ and CH₃NH₃Br₃ as sensitizers for the preparation of dye-sensitized batteries.Since then,lead based halide perovskite semiconductor materials(APb X₃,Perovskite（hereinafter referred to as perovskite）has attracted extensive attention in scientific research and industry because of its excellent photoelectric physical properties（such as adjustable band gap,high carrier mobility,large optical absorption coefficient,etc.）and wide application prospects.After more than 10 years of development,perovskite semiconductor materials have made many breakthroughs in the field of photoelectric conversion devices.But most of the current research focuses on perovskite polycrystalline films and related devices.Due to a large number of amorphous or low crystallinity grain boundaries,polycrystalline perovskite thin films are the main reason for the rapid ion migration and decomposition of perovskite materials at room temperature.The stability of the corresponding photoelectric devices is further than that of crystalline silicon cells,which seriously limits the further improvement of the performance of perovskite photoelectric devices and the commercialization process.Compared with polycrystalline films,perovskite block single crystal or single crystal film has a perfect structure,lower defect density,longer carrier diffusion distance,and better stability,which gradually become the focus of perovskite semiconductor research and device application.In addition,many modern semiconductor devices only use a thin film on the surface of the chip in the order of microns or nanometers,such an extremely thin film can not be obtained by cutting large crystals,and now the growth of semiconductor film is not a simple material preparation technology,but a device manufacturing process.Therefore,it is of great scientific and practical significance for the further development of perovskite optoelectronic devices to explore and study reliable growth technology,prepare high-quality perovskite single crystal thin film,and systematically study its photoelectric physical properties.Based on the above purposes,CsPbX₃（CPX）single crystal films were grown on Sr Ti O₃（STO）and Si single crystal substrates by laser pulse deposition technology（PLD）.The epitaxial growth behavior of perovskite single crystal was studied,and the band gap regulation and preliminary application of solar cell devices were realized by semiconductor alloying technology.The main research contents and results are as follows:1.Pulsed laser deposition technology was used to grow CsPbX₃ single crystal thin films on STO（001）substrate by pseudocrystalline epitaxial growth mode,and the energy gap control of perovskite single crystal thin films was realized by halogen composition control.The thickness of epitaxial layer can be adjusted precisely by controlling the growth parameters of PLD.The epitaxial thin films within the critical thickness range have high optical quality and very low defect state density,and the epitaxial single crystal thin films have high quasi intrinsic single crystal characteristics.By replacing X with halogens I/Br/Cl and their mixtures in different proportions,the band gap of CsPbX₃ epitaxial films is regulated from 1.75 to 2.98 e V,covering the entire visible luminescence region（400 to 720 nm）,and using the stress effect of perovskite substrate and interface,The stability of the crystal structure of perovskite alloy films is improved significantly.2.The epitaxial growth of CsPbX₃ perovskite single crystal thin films on Si（001）substrate was realized by pulsed laser deposition technology through non-coherent layer by layer epitaxial growth.By ptimizing the parameters of PLD growth temperature and deposition rate,the continuous smooth CPX single crystal film was grown by using PLD non-coextension technology.3.A perovskite solar cell was constructed with p-Si/n-CsPbI₂Br epitaxial structure:FTO/Ti O₂/CsPbI₂Br/p-Si/Au,Perovskite solar cells（PSCs）were constructed with p-Si/n-CsPbI₂Br epitaxial structure,and the optimal efficiency was 9.75%.and the relationship between cell performance and epitaxial heterojunction structure was explored.The good epitaxial relation reduces the defect density at the interface and thus reduces the generation of leakage current.Besides,the epitaxial films have high film quality and clean band gap.The performance of these films is conducive to the transmission and extraction of photogenerated carriers in solar devices,and reduces the probability of non-radiative recombination of photogenerated carriers,so that the performance of PSCs can be improved greatly.In atmospheric environment,the stability of p-Si/n-CsPbI₂Br perovskite cells is significantly improved than that of traditional P-i-N perovskite cells.