Preparation Of Planar Inverted Perovskite Solar Cells Based On Doped Nickel Oxide Hole-Transporting Layer

In recent years,perovskite solar cells（PeSCs）based on organic-inorganic hybrid perovskites(ABX₃,A = Cs⁺,CH₃NH₃+（MA⁺）,NH=CHNH₃⁺（FA⁺）;B = Pb²⁺,X = Cl^-,Br^-,I^-)have become a “rising star” in the new photovoltaic technology benefiting from their unique advantages,such as intense light absorption coefficient,low defect density,low exciton binding energy,long electron and hole diffusion length,low-cost fabrication technologies,high photoelectric conversion efficiency and et al.In particular,the inverted planar heterojunction PeSCs have become a research hotspot due to the relatively easy fabrication process.The hole-transport materials in the inverted planar heterojunction PeSCs play a very important role in the efficiency and stability of the devices.Nickel oxide（NiO_x）hole-transport material has recently gained a lot of attention due to its good chemical stability and high efficiency of the solar cells.NiO_x-based PeSCs show good photovoltaic performance mainly because the valence band of NiO_x is well aligned with that of organometallic halide perovskites for hole collection/transport,resulting in the high open-circuit voltage（Voc）of PeSCs.However,resulting from the poor conductivity of NiO_x,the photovoltaic performance of NiO_x-based PeSCs is still not satisfactory when compared to the performance of organic hole-transport materials because of the lower fill factor（FF）or short-circuit current density（Jsc）.Therefore,improving the electrical conductivity of NiO_x is a key to improve the performance of NiO_x-based PeSCs and doping is the most effective way to mitigate the problem.In this thesis,metal elements are introduced as the dopants to improve the electrical conductivity of NiO_x.The optical and electrical properties of doped NiO_x thin films are investigated.The influence of doped NiO_x thin films on the properties of perovskite films and PeSCs are studied.Firstly,we demonstrate high-performance inverted planar heterojunction MAPbI3 PeSCs based on the novel inorganic hole-transporting layer（HTL）of silver（Ag）-doped NiO_x（Ag:NiO_x）.It is found that appropriate Ag doping（2 at%）can increase the optical transparency and hole mobility of NiO_x films in comparison with the pristine NiO_x films.Moreover,the MAPbI3 perovskite films grown on 2 at% Ag:NiO_x exhibit better crystallinity,higher coverage and smoother surface with densely packed larger grains than those grown on the pristine NiO_x film.Consequently,the Ag:NiO_x HTL boosts the efficiency of the inverted planar heterojunction PeSCs from 13.46%（for the pristine NiO_x-based device）to 16.86%（for the 2 at% Ag:NiO_x-based device）with a open-circuit voltage（Voc）of 1.07 V,short circuit current（Jsc）of 19.70 mA/cm2 and fill factor（FF）of 80 %.Furthermore,the environmental stability of PeSCs based on 2 at% Ag:NiO_x HTL is dramatically improved compared to devices based on organic HTLs and pristine NiO_x HTLs.Secondly,the high-performance inverted planar heterojunction mixed-cation MA_0.9FA_0.1PbI₃ PeSCs based on the silver（Ag）and lithium（Li）co-doped NiO_x（Li:Ag:NiO_x）HTL are demonstrated.The results show that Li,Ag-codoping can further increase the optical transparency and hole mobility of Ag:NiO_x films.Moreover,the MA_0.9FA_0.1PbI₃ perovskite films grown on Li:Ag:NiO_x exhibit uniform and dense surface with stronger light absorption than those grown on the Ag:NiO_x film.Consequently,compared to Ag:NiO_x HTL,the application of Li:Ag:NiO_x HTL can effectively improve the short circuit current（Jsc）and fill factor（FF）of the inverted planar heterojunction mixed-cation PeSCs.Furthermore,the environmental stability of MA_0.9FA_0.1PbI₃ mixed-cation PeSCs based on Li:Ag:NiO_x HTL is dramatically improved compared to MAPbI3 and MA_0.9FA_0.1PbI₃ devices based on Ag:NiO_x HTLs.These works provide the simple and effective HTL material systems for high-efficient and stable PeSCs.