Crystallization Kinetics Regulation And Photoelectric Performance Study For Tin-based Perovskite

Perovskite solar cells（PVSCs）have achieved a power conversion efficiency（PCE,25.8%）comparable to commercial silicon-based solar cells due to their superior optoelectronic properties.However,the environmental pollution caused by lead halide perovskite has significantly impeded the large-scale manufacturing and commercialization of lead-based PVSCs.The most effective way to solve the problem is to replace lead with fewer or non-toxic alternative elements,such as tin（Sn）,bismuth（Bi）,germanium（Ge）,antimony（Sb）,and copper（Cu）.Among them,tin halide perovskites have an optical band gap closer to the Shockley-Queisser limit,higher carrier mobility,and longer hot carrier lifetime than lead-based perovskites.Thus,tin-based PVSCs are considered to be the most potential candidates for lead-based PVSCs.Currently,the certification efficiency of tin-based PVSCs has exceeded 10%,but it is still far from the theoretical efficiency（33%）.Generally,the efficiency gap is largely related to the poor quality of tin halide perovskite films due to the lack of effective modulation of the crystal nucleation and growth process.This paper focuses on the crystallization process of tin-based perovskite precursor solution,aiming to achieve the regulation of tin-based perovskite crystallization process and the passivation of crystal defects through additive engineering and green anti-solvent engineering,in order to obtain efficient and stable tin-based perovskite solar cells.The research contents are as follows:（1）Acetic acid（HAc）has been introduced into the precursor solution to promote the formation of prenucleation clusters,thus inducing rapid nucleation for effective regulation of crystallization kinetics.The acidic environment created by the hydrogen ions of HAc and the strong interaction between the acetate ions（Ac^-）and Sn²⁺maintain the stability of Sn²⁺.In addition,the hydrogen bond interaction between HAc and iodide ion（I^-）greatly reduces the loss of I^-during the preparation process of perovskite film,thus ensuring the chemical stoichiometric ratio of I^-/Sn²⁺in perovskite films is close to the theoretical value,effectively reducing the lattice distortion and defect density in perovskite films.Finally,the tin-based PVSCs prepared by HAc as an additive achieve a PCE of 12.26%and an open-circuit voltage of up to 0.75V.The unencapsulated device maintains nearly 90%of initial efficiency even after 3,000 hours storage in a nitrogen atmosphere.（2）HAc has been used as anti-solvent to regulate the crystallization process of tin-based perovskite precursor solution.On the one hand,HAc can accelerate the nucleation rate of precursor through salting-out crystallization,that is,hydrogen bonds can be formed between HAc and precursor solvent to weaken the solvation of Sn I₂ by DMSO,increase the effective concentration of pre-crystallized substances and make the substances to be crystallized from solution.On the other hand,the hydrogen bond between HAc and organic ammonium salt delays the continuous growth of perovskite phase due to the slow volatilization of HAc during annealing.In general,such a fast nucleation process and slow crystal growth process is favorable for the preparation of high-quality tin-based perovskite films.In addition,the un-volatilized residual HAc also plays an obvious passivation effect on the defects in the obtained tin-based perovskite films.As a result,the HAc-traeted device implements a high efficiency of 12.78%（open circuit voltage of 0.92 V）,which is the highest efficiency of tin-based perovskite device prepared by green anti-solvents to our knowledge.Furthermore,we point out that HAc congeners,which are less capable of forming hydrogen bonds with organic ammonium salts than HAc,are also shown to have potential as anti-solvents.