Study On The Optoelectronic Properties Of Cesium Tin Halide Perovskites Film

Halide lead-based perovskite has excellent photoelectric properties.It has been widely researched and applied in solar cells,light-emitting diodes,nuclear radiation detectors,optical fibers,photocatalysts and lasers.However there is toxic lead（Pb）in it,so people hope to develop environmentally friendly lead-free halide perovskite materials with excellent optical and optoelectronic properties.The excellent optoelectronic properties of Pb-based perovskites come from the outermost layer of Pb²⁺6s² lone pair of electrons,and Sn²⁺also has an outer lone pair of electrons 5s²,and the ionic radius and electron configuration are similar to those of Pb²⁺.Compared with lead-based perovskites,the forbidden band width of halide tin-based perovskites is closer to the Shockley-Queisser limit,and is theoretically more suitable for PSC（perovskite-type solar cells）applications.More importantly,Sn is a low-toxic element.Sn²⁺ions exposed to the air will degrade into eco-friendly Sn O₂,which is much less harmful to the environment than Pb.So we used pulsed laser deposition（PLD）technology to deposit halide tin-based perovskite on different substrates to study its luminescence and photoelectric properties,in preparation for further exploration in the future to make optoelectronic devices.Firstly,high-quality Cs Sn Br3 films were grown on Sr Ti O₃,Mica,Si,Si O₂,La Al O₃,Al₂O₃ substrates by pulsed laser deposition technology,and the phases were characterized.The PL peak of the CsSnBr₃ film is about 695 nm,and the band gap is about 1.78 e V.The slight blue shift of the PL peak position of the film at 3.11 nm with the increase of temperature indicates that the film has few defects and stable quality.The carrier lifetime of the CsSnBr₃ film obtained by fitting the TRPL curve is as high as 6.01 ns,and the film has few inherent defects and other non-radiative coincidence channels.The carrier mobility of the CsSnBr₃ film is calculated according to the transverse IV curve of the Cs Sn Br3 film.The carrier mobility of the CsSnBr₃ film is tens cm²·V^-1·S^-1 on the insulator,and the carrier mobility of the film on the Si wafer has reached 1300 cm²·V^-1·S^-1 indicates that the interface between the CsSnBr₃ film and Si is in good condition,and a heterojunction is formed.The CsSnBr₃/Si heterojunction has an open circuit voltage as high as 1 V in the subsequent vertical photovoltaic test.After that,I doped CsSnBr₃ to control the band gap of the film to obtain a thin film with a narrower band gap and a wider spectral range that is more conducive to light absorption.Cs Sn Br_xI_3-x（x=0,1.5）film was deposited on Si O₂,Al₂O₃ substrates.The phase characterization and optical characteristics were tested.The PL peak positions were at 951 nm and 814 nm,and the band gap was 1.38 e V and 1.53 e V,respectively.The emission spectrum of Cs Sn Br_xI_3-x（x=0,1.5,3）was in a wide range from visible light to near infrared region.The longitudinal I-V curve of Cs Sn I₃/n-Si shows that the two do not form a heterojunction.This is because the band gap between the two is very similar,and Cs Sn I₃ and n-Si form an ohmic contact.Halogen anion exchange for CsSnBr₃ will cause the perovskite material to become unstable.Finally,4%Eu²⁺is added to CsSnBr₃ to obtain a relatively stable and multicolor emission film by replacing metal cations.0.04Eu-CsSnBr₃ film was deposited on a Si O₂substrate and the phase was characterized.The PL peaks of the 0.04Eu-CsSnBr₃ film were at 480 nm and 690 nm,respectively.The 480 nm broad peak came from Eu²⁺’s 4f⁶5d¹→4f⁷transition,The 690 nm peak is from the intrinsic transition of the CsSnBr₃ film.