Research Of Photodetectors Based On Se-film/Organic Semiconductor Heterojunctions

Photodetectors（PDs）are one of the most important devices,which are widely used in information conversion,image storage,and tail flame detection.Generally,silicon based materials with high carrier mobility are used,but their further development is limited by their low light absorption and limited response wavelength range.At the same time,inorganic semiconductor materials have problems such as high-temperature synthesis,complex processes,and low flexibility.There are fewer intrinsic p-type materials in inorganic semiconductor materials,and the stability of p-type doped semiconductors is poor.Therefore,the preparation and design of novel low-dimensional intrinsic p-type inorganic semiconductor materials is an effective solution.Selenium（Se）is an intrinsic p-type elemental semiconductor with a melting point temperature as low as 217℃,leading to prepare low-dimensional morphological structures at low temperature.Se exhibits good photoelectric response and fast response speed in the wavelength of ultraviolet-visible range,and is widely used in photoelectric detection.However,the high light reflectivity of Se leads to low responsivity.Organic semiconductor materials are widely used in optoelectronic devices due to controllable energy band,good solubility,easy processing,light and flexible,reduced the reflection of incident light and improved light absorption.Heterojunctions based on novel low dimensional Se structures and organic semiconductors can exhibit their excellent photoelectric properties.Self-powered inorganic/organic photodetectors with high performance are of great significance for the research of new photodetectors.The main research results are as follows:1.In order to improve the photoelectric performance of Se microtubes（Se-MT）,Spiro-MeOTAD as one of organic semiconductor materials with the advantages of non corrosivity and high hole mobility,was used as a hole transport material to construct a Se-MT/Spiro-MeOTAD heterojunction photodetector.Compared to the single Se-MT device,this device shows optical response in the wavelength range of 350-800 nm with self-powered ability.It exhibits the maximum responsivity of 36.5 m A W^-1（10 times enhancement）,the switching ratio of 156（800%enhancement）,the rise and fall times reduced to 22 ms and 35 ms,indicating that Spiro-MeOTAD can significantly improve the responsivity,switching ratio,and response speed of heterojunctions.Considering practical application,it is found that Se-MT/Spiro-MeOTAD PD has poor thermal stability（no photoelectric response after pretreatment at 70℃）and environmental stability（no photoelectric response after being placed in an air environment for one week）.2.In order to improve the stability and photoelectric performance of the device and optimize the device structure,CNT:Ti O₂ doped Spiro-MeOTAD（Spiro-MeOTAD-1）and Se foam（Se-F）were used to build Se-F/Spiro-MeOTAD and Se-F/Spiro-MeOTAD-1 PDs.Compared to Se-F/Spiro-MeOTAD PD,Se-F/Spiro-MeOTAD-1 PD with improved photoelectric performance and stability,exhibits a maximum response of 109.8 m A W^-1（increasement of 2600%）and a switching ratio of 5×10³（increasement of 14.75 times）,with a response time of 19.3 ms/30.2 ms.The photocurrent of Se-F/Spiro-MeOTAD-1 PD after placed one month only decreases by 11%of the origin value with the stability increased by 1780%.After pretreatment at 140℃,it still has a switching ratio of 3.ZnO/Spiro-MeOTAD-1 PD has been prepared to verify the universality of Spiro-MeOTAD-1 using ZnO nanoparticles.The results shows that Spiro-MeOTAD-1 can improve the response speed and responsivity of ZnO,exhibiting good thermal stability and environmental stability.3.In order to simplify the process,reduce costs,reduce the use of dopants,P3HT:Graphene was used to be the organic semiconductor layer,where the poly-3hexylthiophene（P3HT）increases high stability and graphene improves the charge transfer ability.In order to further improve stability,a free-standing Se thin film（Se-P）with high crystallinity was grown by vapor deposition to construct a Se-P/P3HT:Graphene PD.After placing the device at 25℃for one month,the photocurrent of Se-P/P3HT:Graphene PD remains at 90%of the original value.After pretreatment at 140℃for 1 h,the switching ratio of Se-P/P3HT:Graphene PD decreases from289 to 17（retention of 5.9%）.The above results indicate that the Se-P/P3HT:Graphene PD exhibits good environmental stability and thermal stability than Se/Spiro-MeOTAD.