Fabrication And Mechanism Research Of Photomultiplication Type Organic Photodetectors Based On Hole Tunneling Injection

Photodetector as a significant unit of intelligent optoelectronic systems has stimulated immense attention from multidisciplinary areas.Photomultiplication(PM)is desirable for highly sensitive photodetectors with excellent capability of weak light detection,which can avoid the use of complex pre-amplifier circuit,further simplify the design of photodetection systems and cut costs,and benefit the development of integrated optoelectronic products.For organic photodetectors(OPDs),PM phenomenon cannot be realized by utilizing the principle of avalanche effect or impact ionization as in inorganic materials,stemming from organic semiconductor materials with large exciton binding energy.Charge tunneling injection induced by interfacial traps becomes the mainstream working mechanism for obtaining PM type OPDs.The research work of this paper is focused on the PM type OPDs with single carrier transport property.From the point of view of device physics,through interface engineering,the design of device structure and the selection of materials,the response spectrum of PM type OPDs is broadened and the PM type OPDs with adjustable spectral response is realized.It also provides a new insight on realizing the PM type OPDs with single carrier transport property.The main contents and conclusions in this paper include:(1)Realize the tunable spectral response range PM type OPDs working under bidirectional bias.All the PM effect under forward bias and reverse bias results from the hole tunneling injection assited by interfacial band bending induced by electron trap.The EQE spectra under forward bias and reverse bias depend on the distribution of trapped photogenerated electron near the injected electrode.The broadband and narrowband spectral response were achieved by adjusting the optical field distribution in device and then the the distribution of trapped photogenerated electron near the injected electrode.The PM type OPDs working under bi-directional biases would possess wide potential applications,especially in integrated optoelectronic products.(2)Fabrication the PM type all-polymer photodetectors with PBDB-T:PZ1 as active layer.This PM type all-polymer photodetectors exhibits single-carrier transport property.The PM effect results from the fact that the isolated polymer PZ1 surrounded by polymer PBDB-T can act as electron trap to capture photogenerated electron,which induces the interfacial band bending for efficient hole tunneling injection.(3)Realize the broadband PM type OPDs based on PBDB-T:IEICO-4F(1:1,wt/wt)/PBDB-T:IEICO-4F(100:3,wt/wt)double active layers.The photogenerated electrons in PBDB-T:IEICO-4F(1:1,wt/wt)active layer will be transported into PBDBT:IEICO-4F(100:3,wt/wt)active layer under applied bias.The result is that the distribution of photogenerated electron trapped by IEICO-4F in PBDB-T:IEICO-4F(100:3,wt/wt)active layer near the injected electrode exhibits broad spectrum,leading to broadband spectral response.Importantly,the spectral response range of PM type OPDs with double active layers can be extended.(4)The PM type OPDs with bulk heterojunction formed by double donor materials was exhibited and its universality was verified.The PM effect should be attributed to the fact that the small molecular donors can act as electron trap to capture photogenerated electron,which induces the interfacial band bending for efficient hole tunneling injection.There are 111 figures,7 tables and 218 references in this paper.