Preparation And Electrical Properties Of Organic-inorganic Hybrid Perovskite Single Crystals

Organic-inorganic hybrid perovskite materials have been widely used in the fields of solar cells,photodetectors,and radiation detectors,etc.Generally,perovskite single crystal has higher absorption coefficient,longer carrier lifetime and migration length,and higher carrier mobility than its polycrystalline structure.Due to the absence of grain boundaries and the low concentration of defects,the photo-electrical properties of single crystal are obviously better than those of polycrystalline materials.In order to further study the physical and chemical properties of organic-inorganic hybrid perovskite single crystal,the single crystals in bulk and thin film forms with very high quality were synthesized by optimizing two single crystal growth processes,while their electrical properties were also further studied in this thesis.The main achieve of this paper are summarized as follows:1.A series of high-quality MAPb(Br_1-xCl_x)₃single crystals were synthesized by inverse temperature crystallization method with adjusting the solvent ratio,precursor solution concentration and growth temperature.The effects of different Cl contents on the optical band gap and electrical properties of the crystals were studied.Based on the I-V curves,it is found that the single crystal has completely different resistance states with different Cl content.The single crystal presents obvious resistive switching（RS）characteristics when the Cl content is low.When the Cl content is close to 60%,the carrier concentration and mobility of the single crystal reach their maximum values.2.The unique resistance behavior of MAPbBr₃single crystal was further studied.Different from the reported results of MAPbBr₃polycrystalline films,the resistance behavior of MAPbBr₃single crystal shows a diode-like switching characteristics.Both its high and low resistance states are related to the size of the test electrode,and are sensitive to specific wavelengths of light.It is found that this unique resistance switching behavior is related to the trap-controlled space charge limited conductance（SCLC）mechanism and the internal P-N junction formed by the charged defect movement under the action of electric field.3.MAPbBr₃single crystal thin films with high transverse ratio were synthesized by surface modification of the substrate and spatial growth restriction strategy.The effect of the flexoelectric effect on the conductive behavior of the thin film was studied.The strain gradient was generated by applying pressure on the surface of the thin film by atomic force microscopy（AFM）probe.The strain gradient induced the flexoelectric polarization near the probe.The local electric field generated by the deflection polarization can modulate the height of the Schottky barrier at the metal-semiconductor interface（MAPbBr₃）,which affects the transport performance of single crystal thin film.