Research On The Fabrication And Performance Of Hybrid Perovskite Solar Cells Prepared In Ambient Air

Organic-inorganic hybrid perovskite?hybrid perovskite?solar cells have become a research hotspot in next-generation thin-film solar cells due to their simple preparation process,high power conversion efficiencies as well as the use of elements with relatively high natural abundance.Recently,the record of certified power conversion efficiency for laboratory-based perovskite solar cells has been updated to 24.2%,which is a huge progress given that only 3.8%was achieved a few years ago.Since perovskite materials are sensitive to moisture,the preparation of high-efficiency hybrid perovskite solar cells is generally conducted in a glove box filled with inert gas.The use of glove boxes not only increases cost,but also complicates the preparation process.Therefore,studying the preparation of perovskite solar cells in ambient air is of significant importance both academically and economically.The thesis aims to prepare high-performance perovskite solar cells in the ambient air based on the following studies.Firstly,the method and process parameters for the preparation of titanium dioxide?TiO₂?electron transport layer are studied.Secondly,the preparation of perovskite film by two-step method in ambient air is optimized.Thirdly,the properties of perovskite films and solar cells prepared by antisolvent method in ambient air with different humidity levels are studied.Finally,the effect of humidity on the crystallization process of perovskite film is studied systematically,and a humidity-insensitive anti-solvent method is developed.Based on this method,high-performance perovskite solar cells are prepared at a humidity level of90%RH?25??with the best efficiency of 19.5%.The details of studies are as follows.1.The method and process parameters for the preparation of TiO₂ electron transport layer are studied.The TiO₂ electron transport layers are prepared by pyrolysis spray,spin coating and magnetron sputtering,respectively.Three kinds of methylamine lead iodide?CH₃NH₃PbI₃?planar perovskite solar cells are further prepared based on the TiO₂ electron transport layers obtained.The average power conversion efficiency values of the devices are 12.5%,11.5%,and 12.5%,respectively.With less processing time and cost,pyrolysis spraying is more favorable for the deposition of TiO₂ electron transport layers.Besides,it is found that interval spraying improves the coverage of the compact TiO₂ films and reduces its defect density,facilitating the extraction of photo-generated carriers at the interface,leading to devices with higher efficiency.2.The effects of annealing temperature of lead iodide?PbI₂? films and halogen mixing on the performance of perovskite solar cells prepared by two-step method in ambient air are investigated.When the annealing temperature of the PbI₂ films is 90?,the prepared perovskite films are formed by grains compactly aligned,and the films show good morphology and high crystallinity.Using it as absorber layers in mesoporous CH₃NH₃PbI₃ solar cells,a maximum power conversion efficiency of 12.11%is obtained.The PbI₂ layer is optimized by Br doping.When the molar ratio of PbI₂ to PbBr₂ is 83:17,the best power conversion efficiency of the devices is increased to 14.36%.The results provide an important guide to the preparation of high-quality perovskite films in ambient air with two-step method.3.The quality of CH₃NH₃PbI₃ film and the performance of the associate solar cells prepared by antisolvent method in ambient air with a series of humidity levels?0%RH⁶0%RH,22??are studied.The CH₃NH₃PbI₃ films are similar in terms of crystallinity,surface morphology,light absorption and steady-state photoluminescence.The photovoltaic performances of the solar cells are similar.The average power conversion efficiency of all kinds of devices exceeds 15%.After 60 days of storage in the glove box,the efficiencies of all devices remain above 90%of their initial values.The potential effects of exposure of the perovskite precursor solution to the humidity environment are studied.It is found that an absorption of equimolar amount of water by the precursor solution has negligible effect on the performance of the CH₃NH₃PbI₃ film and the associate solar cells.This study reveals the characteristics of preparing CH₃NH₃PbI₃ perovskite solar cells using anti-solvent method in ambient air at low and medium humidity levels,which lays a foundation for further study of the effect of humidity on the anti-solvent method.4.In order to understand why the preparation of high-quality CH₃NH₃PbI₃ films using anti-solvent method fails under high humidity level?70%RH and above,25??,the influence of humidity on the crystallization kinetics of perovskite films fabricated by anti-solvent method is studied.Through investigating the turbidity point phenomenon and the morphology of prepared perovskite films,the mechanism of humidity affecting the spin-coating crystallization process of CH₃NH₃PbI₃ film is proposed.By meeting the need for an appropriate initial nuclei density of the CH₃NH₃PbI₃ film,a humidity-insensitive anti-solvent method is developed.By this method,high-quality CH₃NH₃PbI₃ films and highly efficient solar cells are prepared in ambient air at any humidity level?0%RH to 90%RH?.In particular,a power conversion efficiency of 19.5%is obtained at a humidity level of90%RH?25??.To the best of our knowledge,this is the most efficient device prepared under low and high humidity conditions?>30%RH?.This method totally eliminates the need of gloveboxes during the preparation of perovskite solar cell,which will greatly reduce the fabrication cost of perovskite solar cells and paves the way for the commercialization of perovskite solar cells.