Study On Bromine-rich All-inorganic Planar Perovskite Solar Cells

In recent years,the photoelectric conversion efficiency of organic-inorganic hybrid perovskite solar cell with low cost has realized amazing progress,and its efficiency has exceeded 25%,showing excellent application prospects.However,several problems such as easy attenuation in the air and poor thermal stability still impede its futher development.All the issues can be ascribed to insufficient understanding for some fundamental key problems such as interface electron transportion process and the physics performance of perovskite material.In this paper,we focus on the research of the new electron transport layer and absorber layer for highly stable,effective and low-cost perovskite solar cell.The main innovative works are listed as follows:1.The TiO₂ electron transport layer has been prepared by magnetron sputtering method and spin coating method.Simultaneously,the corresponding all-inorganic Cs Pb Br₃ perovskite solar cell has also been manufactured.The effects of different preparation methods on the physical properties of the TiO₂electron transport layer and the photovoltaic performance of the device have been studied in detail.The all-inorganic Cs Pb Br₃ solar cell based on sputtered TiO₂ layer has a higher efficiency（5.48%）,and the device displays very good stability.Our research shows that compared with the TiO₂ layer deposited by magnetron sputtering method,the TiO₂ layer prepared by spin coating method has a relatively larger optical band gap.This reveals that the light absorption capacity of the TiO₂layer prepared via sputtering technology is relatively weaker.However,the TiO₂layer deposited by sputtering process possesses a higher Fermi level position than spin-coated TiO₂layer,which is more conducive to improving the transport ability of photogenerated electrons.Meanwhile,the conductivity of the TiO₂ layer deposited by sputtering process is higher.The all-inorganic Cs Pb Br₃solar cell with sputtered TiO₂layer exhibits a higher efficiency of 5.48%.In addition,sputtered TiO₂-based Cs Pb Br₃device without encapsulation displays excellent stability after being placed in atmosphere comprising relative humidity of～40%at room temperature for two months.2.Due to the low electron mobility of the TiO₂electron transport layer,a facile room-temperature magnetron sputtering technology was used to deposit compact amorphous Nb₂O₅ electron transport layer.For comparison,crystalline Nb₂O₅ electron transport layer has also been formed after the high-temperature annealing in air.The influences of amorphous and crystalline Nb₂O₅ electron transport layers on the performance of all-inorganic Cs Pb Br₃ solar cells have been carefully investigated.The efficiency of the all-inorganic Cs Pb Br₃ device with an amorphous Nb₂O₅ electron transport layer is enhanced to 5.74%.Our study indicates that the Fermi level position of the amorphous Nb₂O₅electron transport layer is closer to the conduction band position of the all-inorganic Cs Pb Br₃ perovskite absorber layer,which can collect and transport photogenerated electrons more efficiently.Simultaneously,the surface roughness of the amorphous Nb₂O₅ layer is lower,which is conducive to the further growth of the all-inorganic Cs Pb Br₃ perovskite layer on its surface.The all-inorganic Cs Pb Br₃ layer grown on the surface of the amorphous Nb₂O₅layer has larger grains and fewer grain boundaries.The amorphous Nb₂O₅-based all-inorganic Cs Pb Br₃ solar cell realizes a higher efficiency of 5.74%.3.The Li-doped amorphous Nb₂O₅ electron transport layer is used to further improve the efficiency of the cell.The photovoltaic performance of all-inorganic Cs Pb Br₃ solar cell with Li-doped amorphous Nb₂O₅ electron transport layer has been discussed in detail.After Li is doped into the amorphous Nb₂O₅ electron transport layer,the efficiency of the Cs Pb Br₃ device is further increased to 7.06%.Our research demonstrates that the Li-doped amorphous Nb₂O₅ layer possesses higher conductivity,which reduces the interface contact resistance,and accelerates the extraction rate of photogenerated electrons.Through scanning electron microscope testing,it can be concluded that the Li-doped amorphous Nb₂O₅ layer is beneficial to the better growth of the all-inorganic Cs Pb Br₃ layer on its surface,and can improve the density and uniformity of the perovskite layer.The Li-doped amorphous Nb₂O₅-based all-inorganic Cs Pb Br₃ solar cell can gain a higher efficiency（7.06%）.4.In order to reduce the optical band gap of the perovskite absorber layer,All-inorganic CsPbIBr₂ perovskite film has been prepared and used as absorber layer for all-inorganic CsPbIBr₂solar cell.The influences of Zn doping on the physical properties of the CsPbIBr₂ absorber layer and the photovoltaic performance of the corresponding solar cell have been further explored.The efficiency of the Zn-doped CsPbIBr₂ solar cell can reach 9.04%,and the device reveals an excellent stability.This research opens up a new path for development of highly efficient and stable all-inorganic perovskite solar cells.Our research indicates that the CsPbIBr₂ absorber layer has a smaller optical band gap（2.08 e V）in comparison to the optical band gap（2.34 e V）of Cs Pb Br₃absorber layer.This is beneficial for the CsPbIBr₂ layer to absorb more sunlight.Moreover,the CsPbIBr₂ layer also possesses good thermal stability.The solar cells based on the CsPbIBr₂ layer can achieve an efficiency of 7.10%.In order to further improve the efficiency of the device,the performance of Zn-doped CsPbIBr₂ solar cell has been comprehensively investigated.Our study shows that the Zn-doped CsPbIBr₂layer has a lower recombination number of photogenerated carriers.The efficiency of the solar cell with the Zn-doped CsPbIBr₂ absorber layer is enhanced from 7.10%to9.04%.Moreover,the unencapsulated device based on Zn-doped CsPbIBr₂ absorber layer demonstrates outstanding stability after being stored for 60 days in air with relative humidity of～40%at room temperature.