Research Of Perovskite Single Crystal Photoelectric Devices With Precision Control Of Surface States

As the star semiconductor materials of the past decades,organic-inorganic halide perovskite has received a lot of attention from scientific researchers for their excellent optoelectronic properties,such as high carrier mobility,long carrier diffusion distance,low defect density,tunable band gap,high carrier lifetime product and ultra-high defect tolerance.It has been widely applied in the research of various optoelectronic devices,particularly in the fields of photovoltaic devices,radiation detection,light emitting diodes,it has demonstrated the prominent property.However,the performance of photovoltaic devices based on polycrystalline perovskite are still limited by ion migration.Perovskite single crystal,like other kinds of semiconductor single crystals,possess incomparable advantages compared with their polycrystalline materials.There is no grain boundary in the perovskite single crystal,which is the main ion migration pathway.Thus,the ion migration activation energy can be greatly improved and the losses during charge transfer are significantly reduced.Single crystal also has a higher degree of crystallinity which suppresses the defect density further while providing higher stability.Till now,the photovoltaic devices and radiation detectors based on single crystals have got great success.Even though perovskite single crystals can suppress ion immigration caused by grain boundaries,however,some researches have demonstrated there are lots of deep defects mainly on the surface of single crystal which can lead to ion migration and the decrease of the device performance.The main research contents are as follows:1.The growth of MAPbI₃ single crystal and the control of surface defects.Through inverse temperature crystallization strategy combined with space-confined method,the MAPbI₃ single crystal thin films are gowned.Besides,CH₃NH₃I（MAI）treatment method is used to eliminate the electron defects caused by solution corrosion effect towards crystals due to environmental changes.Meanwhile,we have found the excessive MAI can form free ions on the surface of single crystals which can move driven by a strong electric field.Thus,the electroconductibility of the surface of single crystal can be improved,and the surface potential can also be improved by self-doping effect.Removal of surface ionic defects by atomistic surface passivation strategy can remarkably increase the ion migration activation energy and improve dark current stability.It can be significantly reduced device dark currents to introduce the polymer interface layers and in-situ cross-linked interface layers,which can facilitate lower noise in the detector,improves signal-to-noise ratio and enhances device performance.The different surface states can be applied in different kinds of applications.2.Efficient lateral-structure perovskite single crystal solar cells with high operational stability.We fabricated lateral-structure Au/MAPbI₃/C60/BCP/Au perovskite single crystal solar cells.The lateral-structure does not require expensive transparent electrodes which can further promote the light absorption efficiency and make the device immured from strain stress.The excess of MAI treatment of the single crystal can passivate surface defects while increasing the conductivity of the crystal,it is able to reduce series resistance,improve charge collection efficiency,increase the surface potential which is able to optimize anode contact of the solar cell device,which is well-matched to the Au anode for energy level alignment which greatly reduced the voltage losses,and photovoltaic conversion efficiency of over 11.5%is obtained.Perovskite solar cells are achieved based on perovskite single crystals for the first time.Devices show excellent operational stability and no degradation observed after 200 h continuous operation at maximum power point under 1 Sun illumination.3.Highly sensitive coplanar-structure MAPbI₃ single crystals X-Ray detectorsAu/MAPbI₃/Au coplanar-structured perovskite single crystal X-ray detectors are prepared using atomistic passivated MAPbI₃ single crystals.The atomistic passivated MAPbI₃ single crystals have higher ion migration activation energy,which can improve dark current stability and decrease the dark current of the device.The X-ray detectors hence exhibit a record-high sensitivity above 7.0×10⁵μC Gy^-1_air cm^-2,and the X-ray detection limit is down to 1.5?n Gy_air?s^-1.Meanwhile,the devices also exhibit good shelf stability.4.Elimination of interfacial-electrochemical-reaction-induced polarization in perovskite single crystals for ultra-sensitive and stable X-ray detector arrays.We have prepared a coplanar-structure X-ray detector with a p-i-n structure by inserting p-and n-type interfacial layers between an Au electrode and MAPbI₃ single crystal.The addition of the interface layer on the one hand suppresses the electrochemical reaction between Au and halogen under the electric field when an external bias is applied,which eliminates the current polarization effect in the first stage of the dark current output;on the other hand,the dark current of the device is reduced by about three orders of magnitude due to the formation of the p-i-n structure which limits the charge extraction under the reverse voltage,thus reducing the minimum detection limit to 0.1 n Gy_air s^-1.We have finally prepared a coplanar linear detector array for low-dose X-ray imaging application.