Photovoltaic And Thermoelectric Properties Of Inorganic Tin-containing Halide Perovskites

Research and development of clean and sustainable energy is an essential issue for the human society.In recent years,halide perovskite solar cells have attracted worldwide attentions.Since Miyasaka reported the first perovskite solar cell in 2009,the highest power conversion efficiency of perovskite solar cell has reached 25.2%.The study of inorganic tin-containing halide perovskite is in line with the development direction of halide perovskite solar cells,which is more efficient and more stable.On one hand,the inorganization of halide perovskite is one of the most efficient approaches to improve the stability of halide perovskite solar cells;on the other hand,the introduction of tin can optimize the bandgap of halide perovskite,which is of great significance for achieving state-of-the-art halide perovskite solar cells or low-bandgap perovskite solar cells.With ultralow thermal conductivity,halide perovskites also have potential in thermoelectric application.Due to the easily formed tin vacancies,inorganic tin-containing halide perovskites inhabit high electrical conductivity.With low thermal conductivity and high electrical conductivity,inorganic tin-containing halide perovskites meet the requirements of thermoelectric materials.Whether as photovoltaic materials or thermoelectric materials,there are two critical problems for inorganic tin-containing halide perovskites:the perovskite phase stability problem which is caused by the low tolerance factor of inorganic perovskite;the defect problem,which comes from the oxidation of divalent tin.This thesis follows clues of phase-stabilization mechanism and defect regulation in inorganic tin-containing halide perovskite materials.While improving the phase stability of inorganic tin-containing halide perovskite materials,the defect properties are optimized.By using these methods,we first focused on the Cs Sn_0.4Pb_0.6I₃ inorganic tin-containing halide perovskite thin-film solar cell,and then we explored the thermoelectric properties of inorganic tin-containing halide perovskite bulk materials.1)We first optimized the quality of Cs Sn_0.4Pb_0.6I₃ perovskite films and device preparation process.Experiments and theoretical calculations proved that the addition of tin could optimize not only the bandgap of inorganic perovskites but also the phase stability of inorganic perovskite.We determined the 4:6 Sn-Pb ratio,which achieves better phase stability and oxidation resistance while obtaining an ideal bandgap of 1.38 e V.We used"HPb I₃"to improve the stability of the perovskite phase and added Sn F₂ to optimize the film defects.We achieved a 3.52%efficiency of the Cs Sn_0.4Pb_0.6I₃ solar cell.2)By using grain-boundary and surface defect passivation method,we further optimized the quality of the Cs Sn_0.4Pb_0.6I₃ film and obtained a higher efficiency.With Sn F₂?3FACl acting on the film grain boundary,the film grain grew larger,the carrier trap density was reduced,the carrier lifetime was prolonged,which means the film grain boundary defects are reduced and passivated.The device short circuit current is much improved,and the device efficiency is increased to 6.23%.Moreover,with 4AMPI₂ surface defect passivation,the hydrophobicity of the film surface is increased,the carrier trap density was reduced,the carrier lifetime was prolonged,the energy-level alignment was improved on the side of the electron transport layer.The open-circuit voltage was significantly enhanced,and the device efficiency increased to 13.37%.By using double interface defects passivation,the wet stability and thermal stability of the film are greatly improved.After 2800 hours storage in a nitrogen atmosphere,the efficiency of the device was almost unchanged compared to the initial value.The operational stability of the device under the irradiation of 1 sun(LED)in nitrogen is 653 hours for T₈₀ and 1045 hours for T₇₀(T₈₀ and T₇₀ refer to the time when the device efficiency decays to 80%and 70%of initial efficiency,respectively).To our knowledge,we achieved the highest efficiency and best stability for inorganic halide perovskite solar cells with sub-1.4 e V bandgap.3)Even by using the double interface defect passivation,we didn't significantly inhibit the oxidation of Sn²⁺,and the surface recombination velocity is still at a high level,which indicates that the efficiency of Cs Sn_0.4Pb_0.6I₃ solar cells still has excellent potential.There are still many works need to do to solve the oxidation problem.H₂O is used as a Lewis base to further passivate the surface of the Cs Sn_0.4Pb_0.6I₃ films.Once again,we broke through the highest efficiency record of sub-1.4 e V inorganic halide perovskite solar cells.And the efficiency of 15.65%is also the highest efficiency we achieved in this thesis.4)The inorganic halide perovskite Cs Sn I₃ has not only low thermal conductivity but also high electrical conductivity,which is more suitable for thermoelectric applications.The inorganic tin-containing halide perovskite perovskite bulk material was prepared by vacuum-sealed tube sintering.It is found that:i)the addition of 0.5%mole ratio of Pb I₂ can improve the thermoelectric property of bulk Cs Sn I₃.ii)With Ge replacement of Sn,the Cs Sn_0.8Ge_0.2I₃ perovskite phase stability was enhanced.Because of lattice dedects,the room temperature lattice thermal conductivity of Cs Sn_0.8Ge_0.2I₃ is reduced from 0.64 W?m^-1?K^-1of Cs Sn I₃ to 0.48 W?m^-1?K^-1.And the addition of Ge can control the defect concentration of tin-based perovskite so that the conductivity of Cs Sn_0.8Ge_0.2I₃ increased from 86 S?cm^-2 of Cs Sn I₃ to 190 S?cm^-2.Finally,compared with Cs Sn I₃,the room temperature thermoelectric figure of merit of Cs Sn_0.8Ge_0.2I₃ increased by 40%.The highest thermoelectric figure of merit is 0.12 at 473 K.