Enhancement And Electric-Field Modulation Of Photoluminescence From Lead Halide Perovskite Single Crystal Films

Metal halide perovskite materials have shown great potential in the field of high-performance optoelectronic devices due to their excellent optoelectronic properties,such as high absorption coefficient,tunable optical bandgap,low defect density,high defect tolerance,and long carrier diffusion length.The ionic nature of lead halide perovskites makes them highly sensitive to external factors such as pressure,illumination,and temperature.In particular,the electric field provides a simple and effective mean to optimize and modulate the optoelectronic properties of perovskite materials,which is of great significance for enhancing the optoelectronic performance of perovskite materials and devices.The main contents of the paper are as follows:（1）We investigated the enhancement and electrical modulation of two-photon-absorption-induced photoluminescence（TPL）from CsPbBr₃/Si O₂/Au composite structure.First,we successfully prepared CsPbBr₃ microplate and then constructed the CsPbBr₃/Si O₂/Au hybrid structure by transferring CsPbBr₃ microplate to Si O₂-capped Au electrode arrays.A 105.7-fold enhancement of TPL from CsPbBr₃ microplate with hybrid the structure was realized.Based on steady-state and ultrafast spectral measurements,a kinetic model was established and revealed that the TPL enhancement of CsPbBr₃/Si O₂/Au structure originated from comprehensive effects including field localization effect,trap-filling effect,and increased collection efficiency.Furthermore,the electrical-modulated TPL emission from hybrid structure was explored,by applying an electric field along the direction perpendicular to the CsPbBr₃ microplate plane.The result indicated that TPL was related with the direction and amplitude of external electric field.Based on effect,we reached TPL enhancement from the structure ranging from～61.2-fold to 370.3-fold.The TPL enhancement/reduction of CsPbBr₃/Si O₂/Au structure was attributed to vertical-electric-field induced the passivation/activation effect of Br vacancies.In addition,we also achieved dynamic ON/OFF switching of two-photon lasing from CsPbBr₃/Si O₂/Au structure,with a switching ratio of 67:1.（2）We prepared BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal and then investigated the electrical modulation of TPL emission in BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal thin films.The TPL intensity of BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal thin films in the BA₂（MA）_n-1Pb_nI_3n+1/Si O₂/Au structure exhibited an opposite varying behavior,compared to that of CsPbBr₃ microplate with the structure.Through electric-field modulated fluorescence spectroscopy characterization techniques,we revealed that the TPL enhancement/reduction of BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）was attributed to the passivation/activation of negatively charged trap centers（mainly MA vacancies and I interstitial）.As n-value increasing,the TPL tuning range monotonically increased.For BA₂Pb I₄（n=1）microflakes,the TPL intensity increased from～92%to～114%of the intensity at 0 V condition;for BA₂MAPb₂I₇（n=2）and BA₂（MA）₂Pb₃I₁₀（n=3）microflakes,the range was～71%to～139%and～33%to～201%,respectively.Based on the effect,we demonstrated a switchable ON/OFF effect of TPL emission in two-dimensional layered perovskite materials.（3）We studied the electrical-modulated carrier transport at the interface of the CsPbBr₃/WS₂ heterojunction.First,a composite structure of CsPbBr₃/WS₂/Si O₂/Au was constructed.Experimental results revealed a decrease in the fluorescence intensity for both CsPbBr₃ and WS₂ at the CsPbBr₃/WS₂ heterojunction interface,which indicating the formation of a type-II heterojunction.With applied voltage to Au electrode,the electrical-modulated fluorescence intensity of CsPbBr₃ at the heterojunction was found to be dependent on the polarity of the electric field.When the direction of electric field was from CsPbBr₃ to WS₂,the photoluminescence of CsPbBr₃ at the CsPbBr₃/WS₂ heterojunction increased,and when the direction of electric field was opposite,the photoluminescence of CsPbBr₃ at the CsPbBr₃/WS₂ heterojunction decreased,which indicating electric field could promote or suppress the carrier transport at the interface of the CsPbBr₃/WS₂ heterojunction.