Photomultiplication Type Organic Photodetectors With Single Carrier Transport Characteristics

Bulk heterojunction(BHJ)organic photodetectors(OPDs)have the advantages of simple preparation process,easy performance optimization,low cost and environmental friendliness.The performance and parameters of the BHJ OPDs are greatly improved with the development of organic semiconductor materials and device physics.It becomes an urgent scientific problem that how to improve the external quantum efficiency(EQE)and the detection sensitivity of the OPDs.The PM type OPDs with single carrier transport characteristics can be fabricated based on the mechanism of trapped charge inducing opposite charge tunneling injection.The single carrier transport characteristics can effectively inhibit the dark current density and improve the weak light detection ability of the PM type OPDs.In this paper,it's taken as the focus to prepare the PM type OPDs with single carrier transport characteristics.After the fabrication of the active layers,the performance and parameters of PM type OPDs are further improved by adjusting the distribution of photogenerated charge in the active layers.The main research contents are as follows:(1)The PM phenomenon is realized in the all-polymer system according to the working mechanism of hole tunneling injection assisted by trapped electrons.The PM type all polymer photodetectors(all-PPDs)is prepared.The polymer P3 HT and PZ1 were selected as donor and acceptor materials respectively,which have matching energy levels and high hole mobility.The doping weight ratios of P3 HT and PZ1 in the active layer were set as 100:5-100:1 to obtain the optimized light and dark current density.The electron channels are absent in the active layers with rather less PZ1 content.The electron traps are formed with the PZ1 surrounded by P3 HT.The holes are tunneling injected into active layers assisted by the trapped electrons.(2)The performance of the PM type all-PPDs can be improved by controlling the molecular arrangement of P3 HT in the active layer.The active layers with different self-assemble time were prepared.The effect of different self-assemble time on the molecular preferred orientation in the active layer was studied according to the GIXRD curves of the active layer blend films.The hole mobility of the active layers with different self-assembly time were measured.The experimental results showed that the hole mobility could be effectively improved by shortening the self-assembly time of active layers to 5 min.(3)The PM type OPDs with electron transport characteristics were fabricated with polymer PBDB-T and small molecules Y6 as donor as acceptor,respectively.The doping weight ratio of PBDB-T and Y6 in the active layer is set as 1:100-4:100.The effect of the weight ratio of PBDB-T in the active layer on the device performance is studied.The continuous hole transport channels are absent in the active layers with rather less Y6 content.The hole traps are formed with the PBDB-T surrounded by Y6.The electrons are tunneling injected into active layers assisted by the trapped holes.This work demonstrates the universality of the working mechanism and the feasibility of the preparation of the PM type OPDs with single carrier transport characteristics.(4)The performance of PM type OPDs is optimized with interface engineering.The electrons from external circuit are tunneling injected into active layers assisted by interfacial trapped holes in the electron-only PM type OPDs.The distribution of the trapped holes in the active layer can be altered by the insertion of n-type polymer PZ1 between the active layer and electrode.The PM type OPDs working under forward and reverse bias were fabricated with the insertion of the PZ1 interfacial layer.This paper includes 28 figures,67 references.