The Research Of Surface And Interface Regulation Of Perovskite Photodetectors And Their Applications

As important photoelectric conversion devices in the photoelectronic field,photodetectors can convert optical signals into electrical signals that can be processed and used by human beings.It has been extensively applied in many fields of military,industry,and livelihood.Metal halide perovskites(MHPs)exhibit superior photoelectric performance,low cost,solution processing,and flexible compatibility.As the most promising star materials in the field of optoelectronics,MHPs have been extensively studied and developed in a leap forward.Currently,MHPs-based photodetectors have become a hot spot in the field of optoelectronics.Different from the p-n homogeneous junction configuration of conventional silicon photodetectors,MHPs-based photodetectors have heterojunction structures of p-i-n or n-i-p(where p means the hole transport layer,n denotes the electron transport layer,and i refers to the perovskite layer).In planar devices with such "sandwich" structure,there are usually a large number of defects on the surface and interface of perovskites,which causes serious carrier recombination and affects the efficiency of carrier extraction and collection.As an important functional layer in MHPs-based photodetectors,hole transport layer(HTL)plays a role in extracting and transporting holes,adjusting energy level matching,optimizing interface contact.Therefore,in addition to improving the film quality of perovskite,the optimization of the charge transport layer and the interface is also of great significance for the improvement of device performance.This thesis focuses on high-performance MHPs-based photodetectors,with the optimization of HTL and perovskite layer as an entry point to control the interface and surface of perovskite,so as to effectively improve the performance and stability of the device.The main research work are as follows:Firstly,we prepared cross-linked poly(N-vinylcarbazole)(PVK)polymer by lowtemperature solution method,and used it as HTL to construct p-i-n type MHPs-based photodetectors.As HTL in the inverted structure device,the cross-linked PVK not only provides decent hole transport capability,but also meets to high tolerance to polar solvents,providing a favorable substrate for the growth of perovskite layer.The crosslinked PVK-based device has good rectification characteristics and low dark current.Furthermore,the p-type hydrophobic dopant 2,3,5,6-tetrafluoro-7,7’,8,8’-tetracyanoquinodimethane(F4TCNQ)was introduced into the cross-linked PVK to enhance the optoelectronic performance of device.The low LUMO level of F4 TCNQ makes it a strong electron withdrawing ability,which significantly enhances the hole transport ability of the cross-linked PVK.F4 TCNQ can also act as a Lewis base to coordinate with the undercoordinated Pb2+ ions,achieving the bottom passivation of the perovskite layer.Therefore,doping of F4 TCNQ realizes the optimization of the interface energy level and contact,reduces the defects of the interface,and significantly inhibits the carrier recombination in the interface.The MHPs-based photodetector with F4 TCNQ showed a 20% enhancement of EQE,the dark current and noise current are significantly reduced,the responsivity(R)and specific detectivity(D*)are dramatically improved,and the response speed is shortened by 0.2 ms.The unencapsulated optimized device exhibited good long-term stability with a performance decay of only9% after storing 12 months in the glove box.This work provides a competitive HTL candidate for the construction of high-performance MHPs-based photodetectors,and also paves the way for the optimization of efficient HTL.Secondly,we developed a novel dopant-free phenothiazine HTL,poly(4-(10Hphenothiazin-10-yl)-N,N-bis(4-methoxyphenyl)aniline](PPZ-TPA),which was introduced into p-i-n type MHPs-based photodetectors.This HTL has phenothiazine as the core group of PPZ-TPA,triarylamine as the side chain functional group,and modified by methoxy group.Due to the elaborate structural design,PPZ-TPA exhibits excellent hole transport properties,matched band alignment with perovskite,and excellent defect passivation effect.Based on theoretical DFT calculations and experimental characterization such as XPS and FT-IR,we confirmed that sulfur atoms in PPZ-TPA play a passivating role in perovskite defects by coordinating with uncoordinated lead ions.Furthermore,we compared the performance of PPZ-TPA and PTAA-based photodetectors,and the results demonstrate that the PPZ-TPA-based device has superior photoelectric performance.The PPZ-TPA-based device exhibited more than 85% EQE in the blue light range,the responsivity(R)and specific detectivity(D*)of the device are 0.31 A W-1 and 1.79×1011 Jones at 450 nm,respectively.Moreover,the PPZ-TPA-based device has low dark current and noise current,and the response speed is on the order of nanoseconds.The unencapsulated PPZ-TPA-based device exhibited good stability with little attenuation in responsivity after one year in the glove box.As an application demonstration of the PPZ-TPA-based MHPs photodetector,according to the high response characteristics of this device in the blue light band,we designed and built an underwater blue light communication(UBLC)system,and this photodetector serving as a signal receiving device was successfully integrated into the prototype UBLC test system.The results show that the UBLC demonstration system based on PPZ-TPA device achieves accurate information transmission with a data transmission rate of 300 bps.The MHPs photodetectors based on PPZ-TPA exhibit potential application in the field of blue light communication.This work provides a promising candidate of dopant-free HTL for p-i-n type MHPs photodetectors,and also provides a new idea for the design and selection of HTL in the future.Lastly,in order to broaden the spectral range of the MHPs-based photodetectors and realize the application in the field of near-infrared detection.We partially substituted tin(Sn)for lead(Pb)to form Sn-Pb perovskite,whose spectral range can cover the ultraviolet to near-infrared band.However,Sn2+ is easily oxidized,and the formation energy of Sn vacancy is very low,which leads to a large number of Sn vacancy defects,and then causes undesired p-type doping.Moreover,the high Lewis acidity of Sn2+ will trigger the rapid crystallization process of perovskite,resulting in a rough film surface accompanied by a large number of defects,thus aggravating the nonradiative recombination of charge carriers,resulting in poor performance and stability of Sn-Pb perovskite devices.In order to address the above problems,we proposed a synergistic passivating strategy,with the introduction of a multifunctional additive 4-amino-2,3,5,6-tetrafluorobenzoic acid(ATFBA)to regulate the Sn-Pb perovskite.Through DFT simulation calculations and specific experimental characterizations,we systematically scrutinized and revealed the mechanism of ATFBA improving device performance and stability.The carboxyl and amino groups of ATFBA through chelating coordination and hydrogen bonding to passivate the surface defects of Sn-Pb perovskite.The perfluorinated benzene ring structure affords this passivating agent anchored on the perovskite surface and grain boundaries,and also conferring higher hydrophobicity of the film,which is favorable for passivating defects and improving device stability.In addition,the introduction of ATFBA elevates the conduction band energy level of Sn-Pb perovskite and facilitates the efficient transport of electrons from perovskite to electron transport layer.Benefitted from the synergistic passivating strategy,the ATFBA-treated Sn-Pb perovskite-based photodetector exhibits outstanding performance with a high D* value of 5.34×1012 Jones and an excellent responsivity of0.52 A W-1 at 850 nm,and with more than 75% in the near infrared region.Furthermore,the ATFBA device exhibits an ultra-wide LDR of 224 d B and an ultra-fast response speed of 39.68 ns.More excitingly,the ATFBA-treated Sn-Pb perovskite photodetector retains 97% of its initial responsivity without obvious degradation after being stored for450 days.As an application demonstration of the ATFBA-treated device,based on the high sensitivity and fast response of the device,we designed and constructed a visual pulse oximetry sensing test system.Compared with the test system based on commercial photodetector,the measured heart rate and Sa O2 values of the two systems were within 2% error.This study demonstrates the potential of ATFBA-treated Sn-Pb perovskite photodetector for pulse and blood oxygen sensing system.This work provides a direction for constructing high-performance and high-stability Sn-Pb perovskite photodetectors,and also paves the avenue for the design and selection of passivating agents.