Application Of Interface Passivation Layer In Two-dimensional Perovskite Photodetector

In recent years,due to excellent optoelectrical properties and stabilities,two-dimensional(2D)layered perovskites have been widely used in optoelectronic devices.High power conversion efficiencies have been achieved of 2D perovskite solar cells(PSCs).However,there are few reports about 2D perovskite photodetectors with the same structure of 2D PSCs and larger dark current is observed.The main reason is that many defects existed at the interfaces of the device,which increases the leakage current and lead to the increase of dark current.In order to reduce to the dark current effectively,interface passivation method can be used in the device fabrication process.Though the interface passivation method,the defects of the interface can be passivated effectively,and it can also be used as a carrier blocking layer to reduce recombination and improve the performance of the device.Based on the traditional planar inverted structure,we introduced a thin insulating layer of polymethyl methacrylate(PMMA)or Al₂O₃ between the hole transport layer and the 2D perovskite active layer.This interface passivation method can effectively reduce the carrier recombination and lower the dark current,thereby improving the responsivity and detectivity of the device.There are mainly two parts in this work:(1)Effect of PMMA interface passivation on the performance of 2D perovskite photodetectors.We introduced a thin insulting layer of PMMA by spin coating method.Compared with the control 2D perovskite photodetector,the dark current of the passivated device was significantly reduced from 10^-1 A/cm² to 10^-5 A/cm²at-1 V bias,and the light on/off current ratio was improved.Results show that introducing a thin insulating layer at the interface can effectively reduce the accumulation of electrons at the interface and prevent the recombination of carriers.(2)Effect of Al₂O₃ interface passivation on the performance of 2D perovskite photodetectors.We then used atomic layer deposition(ALD)technique to deposit a thin insulting layer of Al₂O₃,in order to control the thickness of the passivation layer accurately.When the thickness of Al₂O₃ was 2 nm,the passivated 2D perovskite photodetector exhibits low dark current of 10^-8 A/cm²,large on/off current ratio of 10⁵ at-1 V.As expected,the detectivity,responsivity,and EQE of the photodetector have also been significantly improved,achieved 1.32×10¹³Jones,1.7 A/W,and 406%under 532 nm laser illumination with intensities of 53n W/cm²,respectively.This work provides a method to reduce the dark current and improve the performance of 2D perovskite photodetectors.