Syntheses Of New-type Halide Perovskites And Its Application In Photocatalysis And Solar Cells

Halide perovskite material is a new optoelectronic semiconductor material.It has excellent optical properties such as high absorption coefficient,direct band gap and high photoluminescence quantum yield.Therefore,it has been widely studied in solar cells,optical devices and photoelectric sensors.However,perovskite devices have not been commercialized due to insufficient stability.Obtaining highly stable perovskites,understanding its fundamental optical properties and applying it in optoelectronic fields are always the core concerns to be resolved.In this paper,we obtained a stableα-FAPb I₃film via a modified method,and studied its intrinsic optical properties.Moreover,a new-type composite perovskite material,NGQDs-CsPbI₃,was obtained by functionalizing CsPbI₃ quantum dots with nitrogen-doped graphene quantum dots（NGQDs）.Such material exhibits good aqueous stability and can effectively photodegrade organic pollutants when compositing with Ti O₂.Such material also can be used in photovoltaics as absorption layer.The main research results are as follows:（1）A stableα-FAPb I₃ film was synthesized by improving the previously reported method,and its temperature-and excitation intensity-dependent photoluminescences（PLs）were studied.It is found that the crystal phase competition process is extremely complex and disordered at low temperature.The temperature range of biphasic coexistence is 130～160 K.In this process,the PL intensities of high temperature phase（cubic phase）or low temperature phase（tetragonal phase）changes chaotically.After completely transforming into tetragonal phase,the PL caused by crystal defects is significantly enhanced compared with single cubic phase.The two coexisting phases observed inα-FAPb I₃exert stress on each other by tearing the other phase,thus exhibiting disordered competition behavior.Even after completely transforming into a low-temperature phase,the residual stress still produces many defects,and enhances the PL intensity arisen from defects.（2）By compositing NGQDs withδ-CsPbI₃ quantum dots,a new-type water-stable perovskite material,NGQDs-CsPbI₃ nanocrystal,was synthesized.It exhibits excellent photocatalytic performance when compounded with Ti O₂.Under visible light irradiation,it can degrade 89%Rh B dye in water,and maintain 85%degradation efficiency after five experimental cycles.That is,NGQDs-CsPbI₃/Ti O₂has both high stability and recyclability.Through active factor filling method,we found that·O^2-and·OH radicals generated in photodegradation process are the main factors to degrade Rh B.（3）NGQDs-CsPbI₃ nanocrystalline thin films were synthesized and assembled into active layers for solar cells.After preliminary tests,the photocurrent of the solar cell is 1.3 m A/cm²,and its photoelectric conversion efficiency（PCE）is 0.48%.