Low Temperature Fabricated Electron Transport Layers And Highly Efficient CsPbIBr₂ Perovskite Solar Cells

Recently,perovskite solar cells have obtained much attention due to its rapid boom in power conversion efficiency?PCE?.Organic-inorganic hybrid perovskite materials own outstanding absorption coefficient?10⁵?,long diffusion length of charge carrier?¹000 nm?,low exciton binding energy?22 meV?,suitable band gap?1.55 eV?and solution-processed methods.The PCE of organic-inorganic hybrid perovskite solar cells has achieved 24.2%,which is close to that of silicon solar cells.However,the existence of organic cations leads to poor heat stability for devices.The replace them with alkali metal cations can obtain inorganic perovskite materials CsPbX₃?X=Br,I?with high heat stability since 2015.But the PCE for CsPbBr₃ solar cells is impeded due to its high fabricated temperature?>250??,complicated methods and large band gap of 2.3 eV.Although the CsPbI₃ possesses appropriate band gap with 1.73 eV and high PCEs,the bad yellow non-perovskite phase easily forms at room temperature and the desirable black phase requires the transform temperature over 310?.Recently,the mixed-halide inorganic CsPbI_3-XBr_X?X=1,2?with comprehensive properties were put forward.Although the CsPbI₂Br holds low band gap with 1.92 eV,high-temperature and high-humidity badly break its stability.Fortunately,the CsPbIBr₂ perovskite has a high heat stability close to 460?,beneficial band gap of 2.08 eV,and low phase transition temperature,which has gained great attention.However,the TiO₂ is mainly used to electron-transport-layers in CsPbIBr₂ perovskite solar cells at present and its fabricated temperature is over 450?.What's more,the low electron mobility and much oxygen vacancy of TiO₂ are poor for devices.To solve above problems and achieve high PCE forCsPbIBr₂perovskitesolarcells,thelow-temperaturepreparationof electron-transport-layers and performance improvement of CsPbIBr₂ perovskite solar cells are studied.Our research contents and results are presented as follows.?1?In₂S₃ films preparation and characterization.The chemical bath deposition method?70??was utilized to fabricate In₂S₃ films on FTO substrates.The various quality and photo-electricity properties of In₂S₃ films were obtained under 55,70,85and 100 min reaction time.The In₂S₃ films of employing 85 minutes own better surface morphology,compactness,light transmittance,surface roughness and water contact angles.?2?The study of CsPbIBr₂ perovskite solar cells using In₂S₃ films as electron-transport-layers.We employed In₂S₃ films with different water bath time as the electron-transport-layers?ETLs?,andbuildedadevicestructureof FTO/In₂S₃/CsPbIBr₂/sprio-OMeTAD/Ag.The PCEs of devices are associated with the water bath time.The highest PCE of 5.59%was achieved when the reaction time is 85mins.It is found that the cells with In₂S₃ films as electron-transport-layers improve efficiency and stability by 10%and 87.5%compared with the same structure cell employing TiO₂ as electron-transport-layers,respectively.In addition,the relationship between the properties of In₂S₃ and TiO₂ films as electron-transport-layers and the improvement of cells efficiency were studied.?3?The study of CsPbIBr₂ perovskite solar cells using SnO₂ films as electron–transport-layers.It is confirmed that the SnO₂ films prepared by one-step spin-coating method have the advantages of high light transmittance,compact morphology and low surface roughness.The CsPbIBr₂ perovskite films with good crystallization,large grain sizes and smooth surface were obtained by using the spin coating technology with complementary high and low revolution and the gradient annealing method.The device structure with ITO/SnO₂/CsPbIBr₂/sprio-OMeTAD/Ag was constructed and its PCEs under reverse and forward scan directions were as high as 8.38%and 5.68%,respectively.In addition,the statistics PCE values of cells reveal that the preparation process of devices has a good repeatability.This paper provides a new idea for the preparation of electron-transport-layers at low temperature and high-efficiency inorganic CsPbIBr₂ perovskite solar cells,and has guiding significance for the fabrication of CsPbIBr₂ flexible devices.