Modifications Of Interfaces And Hole Transport Layers In The P-i-n Photodetectors Based On FAPbI₃ Thin Films

As organic-inorganic hybrid perovskites are making tremendous progress in the field of solar cells,their excellent optoelectronic properties have aroused the interests of researchers in photodetectors based on organic-inorganic perovskites.By now,perovskite photodetectors have become one of the hotspots in the fields of optoelectronic devices.It is well known that dark current is the main factor limiting the performance of photodetectors.Therefore,suppressing dark current through appropriate strategies is the key to improving device performance.In this thesis,we demonstrate the p-i-n photodetectors based on?-FAPbI₃ thin films.To reduce the dark current and improve the performance of the photodetectors we employ a suitable interface modification layer and a modified hole transport layer and investigate their effects on device performance.The thesis includes the following two parts:1.Conjugated polymer electrolyte PFN is introduced as a cathode interface modification layer to decrease the dark current of the?-FAPbI₃ film photodetectors.The device performance is improved and the effect and mechanism of the PFN modification are analyzed.?1?Three-dimensional?-FAPbI₃ thin films are prepared by one-step anti-solvent method,and the crystal structure,morphology and optical properties were characterized.The photodetector with a structure of ITO/PEDOT:PSS/?-FAPbI₃/PC₆₁BM/PFN/Al structure is constructed,where PEDOT:PSS and PC₆₁BM serve as the hole and electron transport layers,respectively.PFN is introduced as the cathode interface modification layer to reduce the dark current and improve performance.The device shows an on-off ratio of2.72×10⁴ at-0.5 V,with a broadband light detection capability from 330 to 800 nm,a maximum EQE close to 64%,responsivity of 0.30 A/W,and a specific detectivity of 5.0×10¹¹Jones.It has a linear dynamic range of up to 136 d B and a fast response in the microsecond range.Besides,the PFN-modified photodetectors can also be self-powered.?2?It is found that PFN has both positive and negative effects on the overall performance of the device,and the mechanism of PFN in the device is analyzed.The blocking of hole injection by the PFN dipole layer and the increase of the hole injection barrier introduced by PFN effectively reduce the dark current of the device under reverse bias and improve the steady-state performance of the device.However,the introduction of a large barrier and low electron mobility of PFN cause the accumulation of photogenic electrons at the PC61BM/PFN interface.The trapping and detrapping effects cause the different dynamic changes in transient photocurrent,namely rising"overshoot"and falling"tails".This mechanism has also been proved by the results of capacitance voltage measurement and impedance spectroscopy analysis.2.Neutral polymer PTAA,which is widely used in perovskite solar cells,is utilized instead of PEDOT:PSS as a hole transport layer to suppress the dark current,and amphiphilic conjugated ionic polymer PFN is introduced to improve the interface compatibility between the FAPbI₃/PTAA interface.The photodetector shows improved performance.?1?The PTAA hole transport layer has better energy level alignment and can block electron injection under a reverse bias.To solve the wetting issue of the perovskite precursor solution on the surface of PTAA,amphiphilic conjugated ionic polymer PFN is introduced in the device,which improves the interfacial compatibility.?2?Based on the PFN-doped PTAA hole transport layer,we fabricate a p-i-n type FAPbI₃photodetector with good performance.The device shows a dark current as low as 8.28×10^-5m A/cm² and an on-off ratio of over 1.30×10⁵at an operating bias of-0.5 V.It achieves an external quantum efficiency of about 63%at around 750 nm,with a responsivity of 0.31 A/W and a specific detectivity of 6.2×10¹³Jones.The device also exhibits fast response speed with rise and fall times of 29.5 and 30.3?s and a-3 d B bandwidth of 978 k Hz.Based on pure?-phase FAPbI₃ polycrystalline thin films,we have improved the performance of p-i-n perovskite photodetector by the interface and hole transport layer modifications.The performance of the devices are improved.Our work provides a feasible way for constructing perovskite photodetectors with high performance.