High Stability Three-dimensional Perovskite Single Crystal Applied In Photoelectric Detectors

Photodetector is a device which could convert optical signals into electrical signals through the photoelectric effect.It has a wide range of applications in academic and industrial fields,including image sensing,optical communication,environmental monitoring and chemical/biological detection.However,due to the limitation of their own defects,traditional semiconductor materials have high requirements for detection environment,which is difficult to meet the current complex market demand.Three-dimensional perovskite material has a structure of ABX₃,with high visible light absorption efficiency,long carrier diffusion distance,adjustable band gap and other excellent photoelectric characteristics,is the ideal material for manufacturing photoelectric devices.Perovskite single crystal material has no grain boundary,continuous and complete lattice,and low defect density.Among them,three-dimensional perovskite single crystal based on methylamine（MA）system has been widely studied due to its superior properties.However,methylamine is volatile and has poor thermal stability.Although the three-dimensional perovskite single crystal based on formamidine（FA）system has a better stability,it is prone to phase transformation at room temperature,which affects the quality of single crystal.Therefore,how to improve the stability of three-dimensional perovskite single crystal is extremely urgent.In order to prepare perovskite single crystals with high stability,we first introduce small-sized Cs and Br into the methylamine-free FAPb I₃ perovskite single crystals.The Cs_0.1FA_0.9Pb I_2.7Br_0.3（Cs FA）perovskite single crystals can inhibit the phase transition of perovskite fromαphase（perovskite phase）toδphase（non-perovskite phase）by releasing lattice stress.However,there are too many internal defects in Cs FA perovskite single crystal,and the quality of crystal is poor,which cannot meet the current needs.Therefore,we chose to dope large-sized guanidine（GA）into Cs FA perovskite and synthesized Cs_0.1FA_0.85GA_0.05Pb I_2.7Br_0.3（Cs FAGA）erovskite single crystals by inverse temperature crystallization method.We found that lattice-incorporated GA can enhance perovskite stability by forming hydrogen bonds and reducing iodine vacancies,but the large-sized GA produces stretching strain,which cause uneven distribution of lattice stress.Therefore,we doped Cs FAGA perovskite single crystal with a small amount of alkaline earth metal Ba（Cs FAGA:Ba）for adjusting the lattice microstrain.Then,we conducted a study on the photoelectric detection performance of Cs FAGA:Ba perovskite single crystal.Through comparison,we found that the crystal quality of the optimized Cs FAGA:Ba perovskite single crystal was improved,and the photoelectric conversion characteristics became better.In the 30-minute response test,the Cs FAGA:Ba single crystal detector did not show any attenuation of response current,showing excellent working stability.Then,in order to improve the stability of wide bandgap MAPb Cl₃ perovskite single crystal,FA was added to MAPb Cl₃ single crystal for regulating the A site,and double-cation perovskite single crystal was synthesized by inverse temperature crystallization method.With the addition of FA and a small amount of Br,the lattice compressive stress of double-cation perovskite single crystal decreases,with improved thermal stability.After a series of experiments,we found that the best component of perovskite single crystal is MA_0.75FA_0.25Pb(Cl_0.94Br_0.06)₃.Therefore,we focus on the photoelectric properties of MA_0.75FA_0.25Pb(Cl_0.94Br_0.06)₃ perovskite single crystal.Compared with the FA-free MAPb(Cl_0.94Br_0.06)₃ perovskite single crystal,MA_0.75FA_0.25Pb(Cl_0.94Br_0.06)₃ device has a higher photocurrent with lower noise,and its dark current density is even as low as 7.3×10^-9 A cm^-2 under the bias of-4 V.