Preparation Of Highly Efficient And Stable Gradient Heterojunction CH₃NH₃PbI₃-PC₆₁BM Solar Cells By Anti-solvent Method

Perovskite solar cells have become the recent research hotspots because of their high energy conversion efficiency and low production cost.The invert-structure planar heterojunction CH₃NH₃PbI₃ cell has a simpler production process and better performance,which is one of the most important research directions.The simplest and most commonly used method in depositing active layer film is one-step spin-coating method,but the CH₃NH₃PbI₃ thin film prepared by the one-step spin-coating method has low coverage,and perovskite grain size is small,which affects the performance of the cell.Therefore,this dissertation works on the adjustment of the precursor solution solute ratio,the concentration of the solution;optimize the annealing process,etc.to prepare high quality CH₃NH₃PbI₃ film.In addition using PC₆₁BM chlorobenzene anti-solvent to form CH₃NH₃PbI₃-PC₆₁BM gradient heterojunction to further improve the performance of the cell.Adjusting precursor solution solute ratio and olution concentration.The precursor solution was spin-coated into a film and characterized by XRD and SEM.It is found that the prepared perovskite film has high coverage,large grain size and few crystal defects when the precursor solution ratio is CH₃NH₃I:PbI₂:DEACl=1:1:0.4 and the solution concentration is 1 mol/L.Corresponding perovskite solar cells have generally higher energy conversion efficiency of 10.68%.The effects of annealing temperature and annealing time on the formation of CH₃NH₃PbI₃ thin films were investigated.The results show that annealing at 90℃for10 min is the best annealing process parameters,perovskite film prepared under this parameter has almost no porosity,good crystal uniformity and high conductivity.Corresponding perovskite solar cells obtained high open circuit voltage V_oc,high short circuit current density J_scc and fill factor FF,and the energy conversion efficiency increased to 12.25%.Introducing solvent engineering.The PC₆₁BM chlorobenzene anti-solvent treatment at 3 mg/mL not only optimizes the quality of the perovskite film,but also penetrates the PC₆₁BM to a certain depth to form the CH₃NH₃PbI₃-PC₆₁BM gradient heterojunction.The CH₃NH₃PbI₃-PC₆₁BM gradient heterojunction shortened the photogenerated electron transport distance and improved the energy level matching between the CH₃NH₃PbI₃ layer and the PC₆₁BM interface,thus further improving the energy conversion efficiency of the cell to 13.5%.Compared with untreated original devices,the device using CH₃NH₃PbI₃-PC₆₁BM gradient heterojunction cell formed by PC₆₁BM chlorobenzene anti-solvent greatly reduces the hysteresis effect of the cell.The scanning path and scanning direction have almost no effect on the J-V curve under test.In addition PC₆₁BM chlorobenzene anti-solvent treatment improves the stability of the device,still maintain 95%of the energy conversion efficiency after a month.