Broadband Photodetectors And Its Application Based On Perovskite And Organic Materials

Photodetector can directly convert external optical signals into electrical signals based on the photoelectric effect,which is playing an indispensable role in many applications,such as military,national defense,environmental monitoring,medical communication,and so forth.The semiconductor optoelectronic materials,such as silicon,III-V composite semiconductors and other traditional photodetectors,have been seriously limited in practical application owing to their complex process,high cost,and insufficient material properties.Nowadays,perovskite materials,which have unique optical and electronic characteristics such as high absorption coefficient,high mobility,adjustable band gap,long carrier diffusion length and solution processability,have triggered significant attention for the exploration of perovskite photodetectors.Polymers or quantum dots are combined with perovskite to broaden the response range.However,it still has low EQE owing to the loss of charge transfer in NIR.Therefore,how to extend the response range to the NIR and prepare perovskite photodetectors with high sensitivity,fast response and high stability is an urgent problem to be solved.In this paper,according to the research status of perovskite,tin-lead perovskite with small optical band gaps and perovskite/organic materials were used to solve the problems of crystal defects and energy level matching in broadband perovskite photodetectors.The main research contents are divided into three parts:Firstly,Sn-Pb perovskite has been proven to possess the advantages of narrower band gap,higher charge mobility and less toxicity compared to the MAPb I₃ perovskite.Partial substitution of Sn into Pb-based perovskites can effectively tune the absorption spectrum to the near infrared region broadening its application prospects.An azobenzene derivative was employed in Sn-Pb perovskite photodetectors for the first time,as a multifunctional additive to dramatically improve device performance and stability.The N=N in azobenzene has been proven to effectively passivate the under-coordinated Pb ions at the film surface,which led to dark current reducing by almost two orders of magnitude(9.61×10^-5 m A cm^-2 under-0.1 V.).This results in the lower noise current(0.42 p A Hz^-1/2)and the fast response speed(42.9 ns),effectively inhibiting the bimolecular and trap-induced recombination and elongating the carrier lifetime.The noise current is converted from 1/f noise to shot noise independent of frequency.Hydrophobic carbon chains of azobenzene derivative dramatically improve the stability,maintaining 90%of original responsivity after almost 300 h in ambient air without packaging.This work provides a new insight into the realization of fast response and high stability Sn-Pb perovskite photodetectors by introducing new organic molecular of defect passivation.Secondly,the absorption range of organic semiconductor materials can reach the near-infrared region.However,its low light absorption leads to low detection degree of organic photodetector.It needs external preamplifier circuit in practical application,which will increase the cost.Due to the high electron binding energy and low carrier mobility of organic materials,organic materials can't achieve rapid charge transfer like perovskite materials,which affect the response time of the devices.Combining perovskites and organic semiconductors can effectively broaden the spectral response range and prepare highly sensitive and fast-response perovskite/organic heterojunction photodetectors.We combined PM6:Y6Se,a donor-acceptor material,with Sn-based perovskite MAPb I₃ to prepare the perovskite/organic heterojunction broadband photodetector with UV-Vis-NIR response.By comparing three devices with different Urbach energy donor-acceptor materials(MAPb I₃/PTB7-Th:FOIC/MAPb I₃/PM6:Y6/MAPb I₃/PM6:Y6Se),the mechanism of disorder on optoelectronic properties,organic heterojunction passivation and charge transfer process of composite devices were studied.Fourier transform photocurrent spectroscopy external quantum efficiency was applied to quantificationally investigate the Urbach energy.The results show that the Urbach energy of MAPb I₃/PM6:Y6Se is the lowest one,in which the device has the lowest dark current.On the one hand,the lower Urbach energy is more matched with the perovskite Urbach energy.On the other hand,the introduction of organic donor acceptor materials can effectively passivate the defects on the crystal surface.The PL peak has a slight blue shift and the carrier transmission time of TRPL is significantly shortened by the study of carrier dynamics.The introduction of PM6:Y6Se bulk heterojunction not only passivates the defects on the surface of perovskite crystal,but also facilitates the extraction and transmission of electrons.The MAPb I₃/PM6:Y6Se heterojunction photodetector achieves a broadband response,in which the external quantum efficiency reaches 80%in NIR.The responsivity is 0.53 A W^-1 and the specific detectivity is 1.12×10¹² Jones at 850 nm.The noise current is 9.79×10^-14 A Hz^-1/2 at 70Hz,close to the ideal noise current,leading to an ultrafast response speed of 32.5 ns.The combination of perovskite and organic materials not only expands the spectral response range of the device,but also improves the performance of the photodetector.The successful construction of high-performance perovskite/organic heterojunction photodetector provides a reliable basis for further photoelectric detection in the NIR field.Finally,photodetectors based on new perovskite and organic material systems are developing towards intelligence,lightweight and miniaturization.Researchers integrate perovskite/organic photodetectors and other electronic components into different systems,showing their application prospects in future development fields.To verify the practical application of perovskite photodetector in different scenes,we integrated the highly sensitive and stable Sn-Pb perovskite photodetector into the NIR acoustooptic conversion system.The system realizes the lossless transmission of audio signal by taking Sn-Pb perovskite photodetector as the optical signal receiver and shows its potential application in encrypted data transmission.This work not only provides new insights for the molecular design of passivated Sn-Pb perovskite photodetector,but also lays a foundation for promoting the application of novel NIR perovskite photodetector.Meanwhile,we successfully integrated the perovskite/organic heterojunction photodetector into the medical monitoring photoelectric sensing system,which shows a hopeful application prospect.The system uses the highly sensitive perovskite/organic heterojunction photodetector as the core element to realize the sensitive detection of NIR light.Perovskite/organic heterojunction photodetector can realize real-time sensing of weak NIR/Vis signals,which proves its wide application prospect in the field of medical detection.It also paves the way for the development of perovskite/organic heterojunction photodetector in practical application.