Research On Multi-functional Organic Photoelectronic Devices Based On Field-Effect Transistor Structure

Organic optoelectronic devices have a broad application prospect in various fields such as flexible displays,energy-saving lighting,solar cells and so on,due to their characteristics of low cost,mass scale processing,and good mechanical flexibility.Organic field-effect transistors?OFETs?paly an indispensable role in flexible logic integrated circuit because of their electric switching characteristic which have drawn great attention.Simultaneously,OFETs also have a good electric signal amplification function because of their field effect structure.Therefore,they are considered as an important way to realize the efficient flexible photodetection and sensor.In this paper,based on the OFETs structure,we built a various field effect structured multifunctional devices which have both the light-emission and photodetection functions by inducing different type of photosensitive layer and light-emission layer.In addition,we achieved photosensitive organic field-effect transistors?PhOFETs?with good photodetection characteristic in 1.3?m¹.5?m waveband by using organic/inorganic hybrid heterojunction as photosensitive layers which can overcome the drawback of weak infrared absorption of organic material.We further investigated not only the influence of the preparation technology of different function layers and the device structure on the optical and electrical characteristic,but also the working mechanism of multi-functional devices.The main research contents and results in this paper are as follows:1.Development of dual-functional OFETs with both the light-emission and photodetection.We induced NPB UV-visble photosensitive layer and CBP:Ir?ppy?3light-emitting layer into a single OFET and accomplished a dual functional OFET with both the light-emission and photodetection.The influence of the thickness of photosensitive layer,incident light power and so on on the photodetection and light emission are studied.Simultaneously,by studying on the working mechanism of the devices,we found that the NPB layer is the crucial layer for both photodetection and light emission.By optimizing the preparation technology of the device,the photon to electron conversion efficiency of the devices reaches 45360%,the photoresponsivity and photosensitivity reach 148 AW^-1 and 2.1×10³,respectively.And the photoresponse time is only tens to hundreads seconds.In addition,the brightness and the external quantum efficiency?EQE?reach 6324 cdm^-2 and 5.65%,respectively.Also,we further studied on the influence of illumination on the light emission performance of the device and found that the brightness of the device was increased from 6324 cdm^-2 to 7195 cdm^-2,and however,the EQE decreased from 5.65%to5.39%.2.Development of the near infrared to visible light upconversion all-organic light-emitting field effect transistor.By inducing VOPc near infrared photosensitive layer into a common OLEFETs,we achieved a new structured near infrared to visible upconversion devices with outstanding performance.When under 808 nm incident light,the upconversion efficiency of the device reaches 7%,which is the highest value of the reported all-organic upconversion device.We studied systematically the influence of the preparation technology of VOPc layer on the structure,abruption spectra of VOPc film.And further on the photoelectric characteristics.We found that the changes from monoclinic to triclinic structure of VOPc film will benefit to the redshift of Q band,and improving the photoelectric characteristic of the devices in infrared band.Meanwhile,we investigated the influence on the photon to electron conversion and upconversion performance of incident light power and bias.By deeply studying the working mechanism of the upconversion,we concluded the key of achieving high upconversion efficiency in OLEFETs structured devices are the signal amplification mechanism of FETs structure and the good performance in carriers transport and EQE of OLEFETs.3.Design and fabrication of infrared photodetector with OFET structure.We implemented the organic/inorganic bulk heterojunction composed by MoO₃ and p-type organic semiconductors to construct several photosensitive layers with the absorption located at the infrared waveband due to the charge transfer in the heterojunctions.We investigated the absorption characteristics of the MoO₃:m-MTDATA?MoO₃:NPB?MoO₃:2T-NATA?MoO₃:TCTA films and realized intensive absorption from 1150 nm to 1560 nm.We further constructed infrared photosensitive OFETs with 2T-NATA:MoO₃ as photosensitive layers.It is found that the smaller the MoO₃ doping ratio was,the large on/off ratio would be.This could be attributed to the decreased hole carriers due to the weakened charge transfer between 2T-NATA and MoO₃.When the 2T-NATA:MoO₃ molar ratio is 3:1,the devices represented superior infrared photo-detection performance with photoresponsivity of 3.03 AW^-1 and photo sensitivity of 228 in the 1310communication waveband.