Research On FASnI₃ Perovskite Solar Cell By Organic Cation Modification

The photoelectric conversion efficiency?PCE?of lead-based perovskite solar cells?PSCs?has been improved to 25.2%,which is due to the advantages of perovskite materials such as adjustable optical bandgap,higher extinction coefficient and excellent carrier transmission capability.However,the toxicity of lead has limited their broad applications and commercialization.Therefore,the exploitation of environmentally friendly PSC technology has become a hot topic in the field of photovoltaic device research.Tin-based perovskite materials display excellent optical and electrical properties,according to their similar ion radius,extinction coefficient and exciton binding energy as lead-based perovskites,which lead to reasonable device performance.The photoelectric conversion efficiency of tin-based perovskite solar cells has reached 12.4%,showing good application prospects.In this thesis,formamidine tin iodide?FASnI₃?perovskite has been chosen for the fabrication of PSCs.Efforts have been devoted to improving the PCE of FASnI₃-based PSCs,such as cation doping,optimizing the film fabrication and adjusting the energy level of hole transport layer?HTL?,etc.Firstly,3,3-diphenylpropylamine?DPPA?cation has been tried to introduced into the FASnI₃ perovskite system,which will greatly improve the film morphology,crystallinity,absorption and stability of FASnI₃ perovskite.All of these can be attributed to the adjustment of the perovskite crystals and the inhibition of Sn²⁺oxidation by the introduction of DPPA cation.Compared to the pristine one,the PCE of DPPA doped FASnI₃ PSC increased from 4.12%to 6.75%.The unencapsulated device maintained 70%of its initial efficiency after being stored in N₂ environment for more than600 h,indicative of good long-term stability.Secondly,by introducing acetamidine?AcA?cation modified FASnI₃ perovskite material,combined with twice spin-coating perovskite solution,the quality of the perovskite film can be effectively improved.Different from DPPA cation,AcA cation has a more similar ionic radius and structure to formamidine?FA?cation,making it easier to enter the crystal lattice of FASnI₃ perovskite.After optimizing the concentration of AcA cation,we prepared the champion PSC based on AcA_0.1FA_0.9SnI₃ perovskite with a PCE of7.04%.Finally,PSCs based on AcA_0.1FA_0.9SnI₃ perovskite has been studied by introducing 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquino-dimethane?F₄-TCNQ?into the poly?3,4-ethylene dioxythiophene?:poly?styrenesulphonic acid??PEDOT:PSS?to adjust the highest occupied molecular orbital?HOMO?energy level.The energy level match of PEDOT:PSS and AcA_0.1FA_0.9SnI₃ perovskite reduces the energy loss of hole carriers at the interface of the hole transport layer,thereby effectively improving the charge transport.The champion PCE of AcA_0.1FA_0.9SnI₃ PSC reached 7.84%with an open-circuit voltage(V_OC) of 0.55 V.We hope to provide some valuable ideas for the development of tin-based perovskite solar cells by introducting these three works.