Study On The Structure Optimization And Active Layer Doping Modification Of Perovskite Solar Cells

In recent years,the perovskite solar cells?PSCs?have become a hotspot in photovoltaic field duo to its simple preparation process,high light absorption coefficient and excellent charge transport performance.Although PSCs are developing rapidly and their power conversion efficiency has been improved continuously,there are still some problems such as high cost and poor stability in natural environment.In view of the above problems,this paper has carried out the following research:First of all,we optimized the structure of traditional mesoscopic PSCs,designed and fabricated a new electronic transport layer with sandwich structure?SS-ETL?,and completed the device assembly under the condition of high humidity natural environment.The structure of PSC was FTO/SS-ETL/CH₃NH₃PbI₃/Spiro-MeOTA/Ag.Among of them,the SS-ETL was composed with TiO₂ blocking layer,TiO₂mesoporous layer and TiO₂ coating layer,which was introduced after the treatment of TiCl₄ solution.The studies had shown that the TiO₂ coating layer had repaired the micro-cracks producing during the later calcination process of the FTO/TiO₂blocking layer/TiO₂ mesoporous film electrode,reduced the charge recombination of the multilayer film electrode,improved the electronic transmission and collection,and increased the power conversion efficiency of PSC from 7.69%to 10.76%.At the same time,the effects of annealing temperature on the properties of perovskite active layer film and solar cell were investigated.The results showed that the optimal annealing temperature of perovskite thin film electrode was 90 ^oC,and the power conversion efficiency of PSC was 13.23%.On the basis of the above structure of electron transport layer,the hole-free-transport layer PSCs based on carbon electrode were designed and fabricated,and the perovskite active layer was modified by Br-doping.The structure of FTO/SS-ETL/ZrO₂/CH₃NH₃Pb(I_1-xBr_x)₃/carbon electrode was assembled.The properties of multilayer thin film electrode and device were characterized and analyzed.The results showed that the perovskite film had complete coverage and high crystallinity,which enhanced the light absorption intensity of the film electrode when x was 0.25.At the same time,the electrochemical impedance analysis showed that the composite resistance of PSC based on CH₃NH₃Pb(I_0.75Br_0.25)₃ perovskite thin film was larger,indicating that it was shown that the thin film electrode had lower charge recombination.Therefore,the power conversion efficiency of the solar cells device was 9.99%.After a very long time of 1344 hours,the photovoltaic parameters of the device still kept above 96%of the initial value,which showed that the solar cell had good stability.Finally,the doped CH₃NH₃PbI₃ with FTO/SS-ETL/ZrO₂/perovskite/carbon electrode was prepared by adding different proportion of NH₄Cl additive into the precursor of CH₃NH₃PbI₃ perovskite.The results showed that the morphology of perovskite thin films was changed obviously by NH₄⁺and Cl^-doping,the crystallinity and the light absorption intensity of perovskite films increased,and the composite resistance of the device was increased.When PbI₂:CH₃NH₃I:NH₄Cl?molar ratio?=1:1:0.8,the assembled PSC achieved 9.01%power conversion efficiency,and the initial value of 96%was retained in the 300 h stability testing,which showed good stability.In summary,the perovskite active film was modified by doping perovskite active layer on the basis of sandwich structure electron transport layer,abandoning hole transport layer and replacing noble metal electrode with carbon electrode.Not only the power conversion efficiency of PSCs was improved significantly,but also the device stability was improved significantly,which gave a good prospect for the popularization and application of PSCs.