Doped MAPbI₃ Perovskite Single Crystal At Pb Site:the Growth And Photophysical Properties

Over the past few years,organic–inorganic halide perovskites（MAPb X₃,MA=CH₃NH₃⁺;X=Cl^-,Br^-or I^-）have attracted great attention due to their optoelectronic applications.The certified efficiency of perovskite solar cells has reached 25.2%by improving the material quality and device interface,which has been the fastest-advancing photovoltaic technology to date.MAPb X₃ perovskites are also applicable in flat panel displays,light emitting devices,X-ray detectors and other semiconductor devices due to their superior optoelectronic properties.However,there is a lack of understanding of the basic physical properties of perovskites,such as bipolar doping and related carrier transport behavior for diode-based applications and transistor technology.These fundamental properties should be sensitive to intrinsic defects and intentional doping.Perovskite polycrystalline films are often accompanied by a large density of charge traps at the grain boundaries andsurfaces.Therefore,polycrystalline films are not good candidates for semiconductor physics study.Perovskite single crystals（PSCs）have been proved to be more ideal for investigating the optoelectronic properties due to their high crystallinity,superior optical and electrical properties,and enhanced stability.Therefore,it is of great scientific and practical improtance for prepareing MAPb X₃ single crystals with highly qulity to explore simple and controllable doping approaches,clarify the doping mechanism,and systematically study their physical properties for the development of perovskite photoelectron devices.Taking this into account,this dissertation mainly focuses on the preparations and photophysical properties of Pb-site ion doped MAPb I₃ perovskite single crystals.The main results can be summarized as follows:（1）The MAPb I₃ and MAPb Br₃ single-crystals were grown,and the explorations and optimization of the growth condition were undertaken further.The results of photoelectric current test of MAPb I₃ crystals show that it has excellent photoconductivity.And,the pressure-induced band gap behavior of MAPb Br₃ examined by situ optical absorption and photoluminescence measurements,which provides the possibility for high pressure to regulate the physical properties of organic-inorganic hybrid perovskite materials.（2）Highly conductive n-type bismuth-doped MAPb I₃（MAPb I₃:Bi）single crystal were successfully grown by Bi³⁺ions incorporated into the perovskite lattice to replace Pb²⁺.With the increase of Bi³⁺concentrations,both the charge carrier concentration and conductivity are increased.The low-temperature photoluminescence spectroscopy confirmed that stable donor levels are formed in MAPb I₃ single crystals by bismuth doping.（3）It was showed that the p-type conductive of MAPb I₃ semiconductor can be efficiently manipulated by metal ion-doped.The introduction of Li⁺and Na⁺changed the quasi-insulating intrinsic conductivity of MAPb I₃ to a highly conductive p-type conductivity.And,we successfully synthesized low-toxicity Pb-Cu Alloyed MAPb I₃ perovskites single crystal with wider band gap by introduceing Cu²⁺replaced Pb²⁺.Meanwhile,the strong reducibility of I^-ion,which reduces part of Cu²⁺to Cu⁺.Cu⁺as p-type dopants induceing extra holes can efficiently tune the electronic properties of MAPb I₃.（4）We achieved an FF recoed of 85.6%of MAPb I₃ polycrystalline film based P-i-N PSC reported to date with stabilized PCE of 20.1%.The PSC device performance improvement is mainly due to the higher film quality of the perovskite absorber,which was grown by spin coating with MAPb I₃ crystals based precursors.Detailed photophysics spectroscopy studies confirm that the low-defect and highly-oriented perovskite film with small Urbach energy is conducive to the photocarriers transportation and extraction,which gives high short-circuit current density and the fill factor record of the PSC.