Ga-SnO₂ Thin Film Prepared By Magnetron Sputtering And Its Application In All-inorganic CsPbBr₃ Solar Cells

As a strong challenger to crystalline silicon solar cells,the power conversion efficiency（PCE）of perovskite solar cells（PSCs）has risen from initial 3.8%to 25.5%today,becoming a research hotspot in the photovoltaic field.Tin oxide（Sn O₂）is an ideal electron transport material due to its high electron mobility,wide optical band gap,good chemical stability and excellent UV resistance.However,the scalable preparation of Sn O₂electron transport material is an important challenge for the commercialization of perovskite photovoltaic technology.The commonly used preparation methods,such as spin coating,chemical bath and electrochemical deposition,are difficult to obtain high-quality and large-area electron transport layers.As one of the most mature vacuum coating technologies,magnetron sputtering has been widely used in the industrial production of optoelectronic devices.In view of the above problems,uniform and dense Sn O₂ films are prepared via direct current magnetron sputtering technology in this work,and applied as electron transport layers for all-inorganic Cs Pb Br₃ based PSCs.The performance of Sn O₂ films are improved by optimizing the sputtering parameters and heat treatment temperature,as well as doping modification,resulting a high-efficiency and stable PSC device.Specifically,the following researches have been carried out:（1）Sn O₂ films are prepared by magnetron sputtering,and spin coating method is used as a comparison.The effect of the films as electron transport layers on the performance of PSCs with the device structure of FTO/Sn O₂/Cs Pb Br₃/Carbon is studied.By optimizing the sputtering time and heat treatment temperature,the device based on the sputtered Sn O₂ electron transport layer achieves a PCE of 6.38%without any interface modification.The unpackaged device still maintains 89%of the original efficiency after being placed in an air environment with a temperature of 25 ^oC and a humidity of 45～50%for 1200 h.In addition,compared to spin coating method,the sputtered Sn O₂ film has lower roughness,higher electron mobility,and better matched energy level with Cs Pb Br₃ layer.Therefore,the efficiency and stability of device based on sputtered Sn O₂ is significantly improved compared with that of spin-coated Sn O₂-based device.（2）To further enhance the photovoltaic performance of PSCs,sputtered Sn O₂ film is modified by doping Ga.On the basis of the above work,the influence of Ga doping content on the composition,structure,morphology of Sn O₂ films and performance of PSCs are systematically investigated.The results indicate that an appropriate Ga doping content is beneficial to offset the oxygen defects and reduce the energy level of the conduction band of Sn O₂ film,thereby increasing the electron mobility and transport driving force.The PCE of the optimized device under 5%Ga doping content is as high as 8.13%,and the short-circuit current density,open circuit voltage,and fill factor are 8.49 m A cm^-2,1.336 V,and 71.73%,respectively,which are obviously improved compared with PSCs based on undoped Sn O₂film.（3）By adjusting the oxygen flux during the magnetron sputtering process,the structure,optical and electrical properties of Ga（5%）-Sn O_x film are studied and the current density-voltage（J-V）curves of the corresponding PSCs are tested.The results reveal that the sputtered Ga（5%）-Sn O_x film with an oxygen flux of 12 sccm has an electron mobility as high as 221 cm² V^-1 s^-1.The higher electron transport ability is beneficial to accelerate the extraction of electrons and inhibit the charge recombination at the interface of electron transport layer/perovskite.Furthermore,the unpackaged device remained 94.5%of the initial efficiency after being exposed to air atmosphere for 1200 h.Finally,The device with an effective area of 1×1 cm² under the optimized experimental parameters is prepared and achieves an efficiency of 5.98%,while maintaining excellent repeatability.