Application Of Hydrogenation Cs₂AgBiBr₆ Perovskite In Solar Cell And Photocatalytic Fields

As one of the renewable and clean energy,the development and utilization of solar energy have become a hot scientific issue.There are three main methods for utilizing the solar energy,including the transformations of solar energy into thermal energy,electricity and chemical energy.Until now,the organic-inorganic hybrid lead（OIHP）based perovskite solar cells have achieved the highest photoelectric conversion efficiency（PCE）of 25.7%,which is comparable with the one of commercial silicon-based solar cells.However,the intrinsic instability of OIHP film caused by volatilization of organic components and the disreputable toxicity of lead element would greatly limit the application of OIHP solar cell.To solve these problems,environmentally friendly and stable inorganic lead-free double perovskite Cs₂AgBiBr₆has become one of the candidates to replace the OIHP solar cells.However,ascribing to the large indirect bandgap of Cs₂AgBiBr₆,it is hard to fabricate the high performance solar cell.Herein,we developed a new doping method of atomic hydrogen into Cs₂AgBiBr₆,which could decrease the bandgap and increase the PCE of Cs₂AgBiBr₆solar cell effectively.In addition,after combining the Cs₂AgBiBr₆with TiO₂,it was applied to photoreduction of CO₂,and the reaction mechanism was further explored.The main contents and achievements in this thesis are listed below:1.By optimizing the one step spin-coating preparation technology of Cs₂AgBiBr₆perovskite film,compact Cs₂AgBiBr₆perovskite films with uniform grains were successfully prepared.After that,a hydrogenation treatment was tried to modify the Cs₂AgBiBr₆perovskite film,which could decrease its bandgap from 2.18eV to 1.64 eV,especially after 1 200 s hydrogenation time.At the same time,both the carrier lifetime and carrier mobility could also be improved from 18.85 ns and 1.71cm²V^-1s^-1to 41.86 ns and 9.28 cm²V^-1s^-1.2.The hydrogenated Cs₂AgBiBr₆perovskite film was successfully fabricated into the solar cell,which improved the PCE from 0.55%to 6.37%.And this is a record high PCE among all the Cs₂AgBiBr₆-based perovskite solar cells.In addition,the hydrogenated Cs₂AgBiBr₆perovskite solar cell exhibited excellently environmental stability（the PCE kept 95%under N₂1 sun light irradiation for 1440 h aging treatment）.By using the X-ray diffraction（XRD）,quasi in-situ TEM,X-ray photoelectron spectroscopy（XPS）analyses and Density Functional Theory（DFT）calculations,it has been confirmed that atomic hydrogen indeed entered into the interstitial sites of Cs₂AgBiBr₆crystal lattice.After doping the atomic hydrogen into Cs₂AgBiBr₆perovskite film,a fully occupied energy level formed upon the maximum valence band,which could further decrease the bandgap of Cs₂AgBiBr₆perovskite film to 1.64 eV（enhancing the light absorption property）.3.By optimized the hot inject method,we successfully prepared the Cs₂AgBiBr₆quantum dots with average grain size of about 10 nm.Cs₂AgBiBr₆/TiO₂heterojunction was fabricated through electrostatic self-assembly method and then applied to photoreduction CO₂reaction.After the addition of Cs₂AgBiBr₆quantum dots,the light absorption property was increased,the carrier lifetime was improved from 1.67 ns to 2.74 ns.In addition,the introduction of Cs₂AgBiBr₆quantum dots would decrease the nonradiative recombination of photo-generated carrier of TiO₂.After a hydrogenation process,photoreduction CO₂property of Cs₂AgBiBr₆/TiO₂heterojunction took a large enhancement.When the mass proportion of Cs₂AgBiBr₆in Cs₂AgBiBr₆/TiO₂heterojunction is 1/50,the average CO yield could reach 327.77μmol g^-1h^-1,which is much higher than the one of pure TiO₂.