Study On Planar Perovskite Solar Cells With Efficient Electron Transport Layer

Perovskite solar cells（PSC）with lead halide octahedron as framework have attracted much interest due to its earth-abundant resource materials,variety prepration methods and excellent optoelectronic properties.Photovoltaic cell using organic-inorganic hybrid perovskite as the absorber material achieved the highest record efficiency over 23%and has a bright future for industrialization.However,several problems such as air stability,heat stability and hysteresis still hinder its futher development.All the problems can be attributed to insufficient understanding for many fundamental key issues such as interface electron transportion process and the physics property of perovskite material.In this paper,we focus on the study of the novel electron transport layer and absorber layer for high efficient,stable and low-cost perovskite solar cel.The main works are listed as follows:1.In order to avoid the low electron mobility and oxygen vacancy in TiO₂electron transport layer,several IIB metal sulfide/selenides have been prepared by magnetron sputte ring and used as novel electron transport layer for PSC.The influence and mechanism of different IIB metal sulfide/selenides electron transport layer on performance of PSC have been carefully studied.Though the analysis of band structure,novel metal sulfide/metal oxide electron transport layer has also been prepared and used as electron transport layer for PSC.Though the analysis for interface electron transportation and physics property of different IIB metal sulfide/selenide films,low temperature magnetron sputtered CdS film can be considered as most ideal electron transport layer for MAPbI₃ solar cell.The reason can be attributed to its matched conductive band value and suitable optical transmittance compared with CdSe and ZnSe.By futher researching on the thickness of CdS film,we found too thin film thickness would lead to serious leak current while too thick film thickness would lead to the decrease of short-circuit current and enhanced contact resistance.MAPbI₃ solar cell with optimized CdS electron transport layer achieved efficiency over 13%with less hysteresis.By studying the advantage and disadvantage of MAPbI₃ solar cell with CdS and electron transport layer,we found CdS/TiO₂ can be a novel electron transport layer to combine the advantage of TiO₂ and CdS in electron transportation and optical transmittance.MAPbI₃ solar cell with CdS/TiO₂ electron transport layer could achieve improved efficiency and air stability2.Nb₂O₅ films were prepared by room temperature oxygen-assited magnetron sputting method and used as novel electron transport layer for PSC.The mechanism and explaination for enhanced efficiency of PSC with oxygen-assist and Cl doing have been studied in detail.UV-VIS absorption and XRD results confirm Cl doping could significantly improve the crystalline and light absorbance of MAPbI₃ film without changing its band gap.PSC with MAPbI_x Cl_3-x could achieve enhanced efficiency compared with PSC with MAPbI₃.Moreover,oxygen-assited magnetron sputting method was proposed to reduce the number of oxygen vacancy without high temperature annealing process.The decreasing oxygen vacancy could lead to the improved optoelectronic properties for sputtered Nb₂O₅ film.MAPbI_x Cl_3-x-x solar cell with oxygen-assited magnetron sputtered Nb₂O₅ electron transport layer achieved a high efficiency over 16%.3.A novel PCBM/Ionic liquid interface layer was proposed to modify the Nb₂O₅/MAPbI_x Cl_3-x interface and effect of interface layer on the peroformance of PSC has been carefully discussed.Our research shows PCBM interface layer could align interface energy level and accelerate the electron transportation rate.The open voltage of MAPbI_x Cl_3-x-x solar cell can be improved from 0.99V to 1.09V by interface modification.However,the bad surface wettability caused by PCBM modification could deteriorate the quality of MAPbI_x Cl_3-x-x film.When using PCBM/ionic liquid as a novel interface modificat layer,the interface energy level could also be aligned without deteriorating the quality of MAPbI_x Cl_3-x-x film.PSC with PCBM/ionic liquid interface layer have achieved a high efficiency over 18%with less hysteresis.4.For the purpose of decreasing the preparation cost of PSC,Nb₂O₅ electron transport layer was prepared by a novel low te mperature solution method.The effect of preparation technique on the pe rformance of PSC has been carefully studied.Our research shows low temperature solution method prepared Nb₂O₅ film has a large band gap and high optical transmittance which could guarantee the high light absorbance for perovskite film.AFM,KPFM and EIS results reveal low temperature solution method prepared Nb₂O₅ film could effectively decrease the surface roughness and work function,improve the interface electron transportation.MAPbI_x Cl_3-x-x solar cell with low temperature solution method prepared Nb₂O₅ could achieve an efficiency over 14%by optimizing the precursor solution concentration.Further optimization for UV/Ozone treatment could decrease the residual organics,improve the surface wettability and quality of MAPbI_x Cl_3-xfilm.The efficiency of MAPbI_x Cl_3-x-x solar cell with low temperature solution method prepared Nb₂O₅ could be further improved by optimizing UV/Ozone treatment time.5.To solve the proble m of heat stability for organic-inorganic hybrid PSC,novel inorganic perovskite CsPbI₂Br and CsPbBr₃ have been prepared and used as absorber layer for hole transport layer-free inorganic PSC with carbon electrode.The effect of alkali metal doing and impure phase on the peroformance of inorganic perovskite solar cell have been carefully investigated.The research provides new insight on development of high efficient inorganic perovskite solar cell.Our research indicates one-step method deposited CsPbI₂Br film could maintain cubic perovskite structure under room temperature and has good heat stability.UV-VIS absorption and XRD results confirm one-step method deposited CsPbI₂Br film has the band gap of 1.9eV with excellent crystallinity.Planar inorganic PSC with as CsPbI₂Br absorber layer,Nb₂O₅ as electron transport layer and carbon as electrode could achieved a best PCE over 10%.However,the open voltage loss of CsPbI₂Br is much larger than MAPbI_x Cl_3-x solar cell.Alkali metal rubidium was futher used to improve the efficiency of CsPbI₂Br solar cell.In order to solve the problem of air stability for CsPbI₂Br solar cell,all bromized CsPbBr₃ solar cell has also been studied.Though optimizing the preparation process,impure phase such as CsPb₂Br₅and Cs₄PbBr₆ can be avoided and inorganic planar CsPbBr₃ solar cell with Nb₂O₅ETL and screen printed carbon electrode achieved a best PCE over 4%with excellent air stability.