Photovoltaic/Multiplier Dual-mode Organic Photodetector Constructed By Interface Controlling

Organic photodetectors（OPDs）have great application prospects in fields of economy,national defense and military due to their advantages of adjustable spectrum response range,large area preparation with solution method and flexible substrate compatibility.Typical OPDs are diode type photovoltaic（PV）devices,which usually work at reverse bias and have advantages such as low dark current and wide dynamic range.However,their external quantum efficiency（EQE）is usually less than 100%.When detecting weak optical signals,the photogenerated current is small,thus signal processing is always combined with pre-amplification circuit in practical application,which complicates the system and increases costs.In recent years,the Photomultiplier（PM）device with EQE much higher than 100%has attracted attention due to its large photogeneration current,which can avoid the use of pre-amplification circuit and has better detection ability of weak optical signals.However,when the optical signal intensity is large,the problems caused by high power consumption such as breakdown and heat dissipation cannot be ignored.Therefore,PV or PM-type single-mode OPDs have limitations,and it is difficult to cope with the increasing multi-scene application requirements.This thesis is based on PV OPDs,which are typically structured like an‘ITO transparent cathode/ZnO hole blocking（electron transport）layer/PBDB-T:ITIC-Th/Mo O₃ electron blocking（hole transport）/Ag anode’,starting from the interface controlling of the barrier layer and the organic photosensitive layer.By introducing carrier traps,OPDs with switchable PV/PM mode are prepared,that is,they work in PV mode under reverse bias（The photogenerated current is based on the photogenerated carriers collected by the electrodes at both ends,ZnO hole barrier layer and Mo O₃ electron barrier layer inhibit dark current under reverse bias）,and work in PM mode under positive bias,and their photoelectric characteristics are studied.The main research contents of this thesis are as follows:（1）ZnO thin films prepared by thermal evaporation method are used as the hole barrier layer of OPDs.During the ZnO growing process,the mismatch of Znand O elements leads to the existence of free Znatoms in the thin films,which play the role of carrier traps and realize PV/PM dual-mode OPDs.In PV mode,the EQE at 640nm is 64.08%,and the specific detection rate（D*）is 2.50×10¹² Jones.The PM model is based on the photogenerated hole trapped by free Znatoms in ZnO thin films,which induce electrons tunneling injection from external circuit.The EQE at 640nm is 287.43%and D*is6.34×10¹⁰ Jones.（2）By controlling interface of the organic photosensitive layer with method of high-temperature annealing,the surface topography defect makes the contact between the organic photosensitive layer and Mo O₃ barrier layer no longer uniform and tight,which is equivalent to introducing carrier traps at the interface,so as to realize PV/PM dual-mode OPDs.In PV mode,the EQE of 640 nm is 5.12%,and the D*is 5.44×10¹¹ Jones.The PM mode is based on the particle morphology of the organic photosensitive layer annealed at high temperature and induced hole tunneling injection from external circuit by trapping photogenerated electrons:EQE at 640 nm is 11122%and D*is 3.85×10¹²Jones.（3）Combining the process of interfacial regulation of barrier layer and organic photosensitive layer,dual-mode OPDs with better performance were prepared.In PV mode,the EQE of 640 nm is 52.87%,and the D*is 4.55×10¹¹ Jones.The PM mode is based on the two kinds of carrier traps above simultaneously trapping carriers and inducing tunneling injection of external circuit charges:the EQE of 640 nm is 7765%,and the D*is 6.34×10¹¹ Jones.For the above typical organic photosensitive layer annealed dual-mode device,facing the weak optical signals detection of 0.07 W/m²,the photogenerated current density in PM mode is 212.1 A/m²,78867.7 times that in PV mode,which can effectively avoid the use of amplifying circuit to extract weak signals.For 247.7 W/m² strong optical signals detection,the photogenerated current density of the device in PV mode is 2.7 A/m²,which is only 0.055%of that in PM mode.In addition,the response times of the dual-mode devices prepared in this thesis are all less than 100μs in PM mode,which is an order of magnitude improvement over the PM devices prepared using active layer carrier traps.The dual-mode device can realize the detection of strong light and weak light by switching between PV mode and PM mode,which provides a solution for the application requirements of multi-scene photoelectric detection in the future.