Growth And Photodetection Properties Of Metal Halide Perovskite Single Crystals

In recent years,organic-inorganic lead halide perovskite materials have achieved rapid development in the field of photovoltaic and optoelectronic fields due to their excellent optoelectronic properties,tunable bandgap and low-cost raw materials,etc.Compared with widely explored perovskites thin-film,single crystalline perovskites possess the advantage of free of grain boundaries,thus for lower trap density,better charge transport properties and higher stability.In the optoelectronic device application,especially for photodetectors,perovskite single crystals have exhibited promising prospect.Despite the great success of the perovskites,the high-toxic lead contained in the active material and the long-term stability are still two serious problems that limit the commercial application of perovskite device.Therefore,from the perspective of materials design,it is significant to develop low-toxic or non-toxic and highly stable perovskite single crystal materials.However,from the previous study,most of the results show that the stability trades off device performance.Therefore,the common object of our work is to balance the device performance,stability,and toxicity issues.In order to contribute to the above goal,the present thesis focuses on the design of the perovskite structure,growth of large size and high-quality singe crystal for the study of intrinsic photoelectronic properties.In detail,the growth strategies of perovskite single crystals,analysis of the reaction mechanism,exploration of the intrinsic optoelectronic properties and design of optimized photodetectors and X-ray detectors are studied as follows:(1)An effective controlled evaporation process was developed to grow high quality two-dimensional(2D)(C6H5C2H4NH3)2PbBr4 single crystal with the area exceeding 200 mm2.Due to the layered structure,ultra-thin single crystal flakes can be obtained by mechanical peeling method.Also,the single crystal shows strong anisotropic optoelectronic properties.Using the(00l)plane of the crystal,planar-type ultraviolet photodetector are fabricated,which shows extremely low noise current(1.57× 10-16 AHz-1/2),large ON/OFF ratio(? 105),high detectivity(1.55 × 1013 Jones)and excellent stability.(2)A high-quality,large 2D diamine-perovskite single crystal(BDAPbI4,BDA2+=NH3C4H8NH32+)was successfully grown by low-temperature gradient crystallization process.Based on the experimental and theoretical calculation results,the crystal exhibits excellent optoelectronic properties and stability.Specifically,it shows high thermal stability(304?),small exciton binding energy(? 70 meV),low trap density(8.7 × 109 cm-3),high charge collection efficiency(???1.45 ×10-3 cm2 V-1)and large ion migration activation energy(Ea=0.88 eV).Benefiting from the effective charge collection and suppressed ion migration,the BDAPbl4 photodetectors exhibit fascinating performance,including low noise current(2.4 × 10-14 A Hz-1/2),large linear dynamic range(150 dB),high responsivity of 927 mA W'-and high operation stability.The diamine-perovskites are expected to achieve balance between device performance and stability.(3)To ensure the stability while reducing the toxicity of perovskite single crystals,a nucleation-controlled solution method was developed to grow large size high-quality Cs3Bi2I9 perovskite single crystals.It is found that the crystal has a wide bandgap(1.96 eV),high resistivity(2.79 × 1010 ? cm),sufficient charge collection efficiency(??=7.97 × 10-4 cm2 V-1),low noise current(2.2 × 10-15 A Hz-1/2),high X-ray absorption coefficient and excellent environmental and thermal stability.Therefore,an X-ray detector was fabricated using(002)plane of the crystal.Under an electric field of 50 V mm-1,the sensitivity of the detector is as high as 1652.3 ?C Gyair-1 cm-2,and the detection limit as low as 130 nGyair-1 s-1.Furthermore,the device exhibits high X-ray imaging capability thanks to its negligible signal drifting and extremely high stability.(4)In order to further improve the performance of perovskite single crystal-based photodetectors,we proposed a pyramidal surface texture strategy on the perovskite single crystals to enhance light-trapping and designed an effective hard-template method to directly grow high-quality surface-textured CH3NH3PbI3 and CH3NH3PbBr3 single crystals.A well-shaped pyramidal texture is formed on the single crystals with much reduced light reflection from?15%to?5%.Besides,thanks to the direct(insitu)growth strategy,the single crystals show high crystalline quality and excellent electrical properties.Furthermore,the planar-type photodetector made from the pyramid-textured MAPbBr3 single crystals exhibits largely enhanced device performance,including higher responsivity,EQE and faster response speed.