Crystal Growth Regulation Of Tin-Based Perovskite For Efficient And Stable Photovoltaic Cells

In the last decade,significant progress has been made in the development of organic-inorganic hybrid perovskite solar cells,with power conversion efficiency exceeding 25%.However,the use of lead perovskite as the light-absorbing layer has limited its commercial application due to the toxicity of ionic lead.Therefore,there is a need to develop lead-free perovskite materials.Among the many lead-free perovskite,tin perovskite exhibit optical and electrical properties similar to the lead perovskite.This is due to the ion radius of tin（1.35?）is slightly smaller than the lead ion radius（1.49?）,the tin ion has a similar outer electron structure as the lead ion,and tin-based perovskite materials have a more suitable band gap（1.2 e V to 1.4 e V）according to the Shockley-Queisser limit theory（about 1.3 e V）.However,the extremely fast crystallization rate of tin-based perovskite and the easy oxidation of Sn²⁺become obstacle to the improvement of the efficiency and stability of tin-based perovskite solar cells.To address these issues,the following aspects are investigated in this paper.（1）This work proposes the introduction of a new intermediate phase adduct SnI₂-DMSO-MAFa in the precursor using the ionic liquid methylamine formate（MAFa）to develop a simple and reproducible method for the preparation of high-quality tin-based chalcogenide films.This stable intermediate phase adduct was able to retard the reaction rate between ammonium salt and SnI₂,thus regulating the crystallization process of tin-based perovskite and inhibiting the formation of SnI₂clusters.In addition,the amine and carbonyl groups in MAFa can repair the iodine vacancies and unliganded Sn²⁺ion defects.These features eventually prepared highly uniform and hole-free tin-based chalcogenide films.The prepared devices exhibit a photovoltaic conversion efficiency（PCE）of more than 10%,a value that is 53%higher compared to the standard standard device（6.6%）.The stability of the devices prepared based on MAFa was significantly enhanced in a micro-oxygen environment,and the initial efficiency of 78%was maintained after 2800 h of storage in N₂ containing50-100 ppm oxygen.（2）In this work,the halogen-mimetic ammonium salt methyl thiocyanate（MASCN）was added to the precursor as a crystallization inducer to modulate the 2D/3D tin-based perovskite crystallization process.Due to the similar ionic radius and low solubility of SCN^-and iodide ions,the crystallization process will preferentially form highly crystalline tin-based perovskite films containing MASCN.Due to the poor thermal stability of MASCN,the less thermally stable MASCN will sublimate during the annealing stage,and the corresponding lattice positions will be replaced by methomyl iodide（FAI）in situ and retain high crystallinity.The 2D/3D tin-based perovskite solar cells prepared based on the crystallization induction strategy achieve a maximum efficiency of 11.5%.In addition,the strategy resulted in improved device storage stability,maintaining 80%of the initial efficiency after 700 h of storage in a glove box.（3）This work proposes the use of pyridine（Py）as a PEDOT:PSS modifier to enhance the PEDOT:PSS conductivity to promote carrier transport.Meanwhile,Py molecules are able to enter the tin-based perovskite precursors at the spin-coating stage,and the N atoms on the pyridine ring interact with Sn²⁺through hydrogen bonding to regulate the 2D/3D tin-based perovskite crystalline growth.This growth substrate modification strategy effectively improves the crystalline quality of 2D/3D tin-based perovskite films,and the highest efficiency of 2D/3D tin-based perovskite solar cells prepared based on these films reaches 10.3%.