Study On Perovskite And Organic Photodetectors With High Detectivity And Responsivity

Photodetectors are of the utmost importance in the fields of imaging,optical communication and biomedicine.So far,commercial photodetectors have been mainly based on inorganic semiconductors which possess high charge carrier mobility and superior stability,but are limited by the complicated fabrication process and high cost.Solution-processed organic-inorganic hybrid perovskite and organic semiconductor materials possess excellent optoelectric properties providing a new way to fabricate high-performance and low-cost photodetectors.Photodetectors based on perovskite and organic materials have attracted much attention,but it still needs to be further studied in tuning the response window and improving the parameters such as detectivity and responsivity.Generally,the strategy of reducing dark current affects the photocurrent of devices,while the responsivity is restrained due to the strategy for narrow response.Herein,the working principles,key parameters as well as research progresses of perovskite and organic photodetectors were described in Chapter 1.The photoconductive layer and donor-node-acceptor（D-n-A）polymer were adopted as charge carrier transporting layers to improve the detectivity of perovskite photodetectors in Chapter 2and Chapter 3,respectively.The phase distribution regulation and dye-sensitized strategy were applied in the active layer to improve the responsivity and tune the response window of organic photodetectors in Chapter 4 and Chapter 5.The main contents are as follows.In Chapter 2,Zn O:PBI-H was used as photoconductive electron-transporting layer to fabricate self-driven perovskite photodetectors with high detectivity.The doping of small organic molecules enhanced the photoconductivity of Zn O:PBI-H,so that the conductivity of Zn O:PBI-H in the dark was much lower than Zn O,and increased significantly under illumination.However,Zn O:PBI-H cannot be directly used as electron-transporting layer since the residual groups on sol-gel Zn O would lead to the perovskite decomposition.0.2 wt%PEIE could inhibit the decomposition of perovskite without hindering the charge carriers transportation.The perovskite photodetectors based on Zn O:PBI-H possessed high detectivity of 2.5×10¹³ Jones as well as fast response speed in the self-driven mode.In Chapter 3,D-n-A polymer that possessed conjugated backbone as donor and electron-deficient side chain as acceptor was used as hole-transporting layer to fabricate perovskite photodetectors with good stability as well as high detectivity.The photo-induced charge transfer occurred between the donor groups and acceptor groups in D-n-A polymer,and the D-n-A polymer with a small amount of electron-deficient acceptor possessed good electron-blocking ability.Compared with the traditional hole-transporting materials,the D-n-A polymer presented better hydrophobicity and could effectively suppress the dark current.The detectivity of perovskite photodetectors based on D-n-A polymer reached 2.2×10¹² Jones at-0.5 V,which was evidently improved.The D-n-A polymer owned better stability than the blended donor and acceptor heterojunction since the self-aggregation was significantly inhibited.In Chapter 4,P0 and Y6 that possessed complementary absorption were used as active layer to fabricate bilayer heterojunction organic photodetectors with double band response and near-infrared multiplication response,respectively,by changing the solvents to adjust the phase distribution.The P0 film fabricated by drop coating could significantly suppress the dark current and had good solvent resistance.The planar heterojunction and bilayer interdiffused heterojunction could be obtained by using solvents with different solubility for P0 to prepare Y6 film.The response window of the devices based on planar heterojunction changed with the bias direction,which was broadband under forward bias and complementary narrowband under reverse bias.However,the devices based on bilayer interdiffused heterojunction presented broadband multiplication response with high EQE of 3500%at 3 V.The phase distribution in the active layer and the response mechanism could be obtained by AFM and plasma combined with absorption spectrum analysis.The photomultiplication mechanism could be further verified by replacing Y6 with PCBM as acceptor and applying P0:Y6 bulk heterojunction as active layer.In Chapter 5,the BODIPY dyes with narrowband absorption properties were loaded on mesoporous Ti O₂（mp-Ti O₂）as active layer to fabricate dye-sensitized photodetectors with photomultiplication and narrowband response.It could be analyzed from absorption spectra that the BODIPY dye bonded with mp-Ti O₂ possessed good solvent resistance.The photodetectors with Ti O₂ filter presented narrowband response with full-width at half-maximum（FWHM）of 45 nm and photomultiplication with high EQE of 534%at-3 V.Besides,the photodetectors owned excellent stability that the EQE showed negligible decay after 12months`storage.The function of each layer was explored by fabricating devices without specific layer to figure out the photomultiplication mechanism,and combined with the morphology analysis,it turned out that the photomultiplication was resulted by the electron injection under reverse bias.The photomultiplication mechanism was further verified by replacing the hole-transporting materials,and the universality of the strategy was verified by applying other dyes as the active layer.