Tin(II) Acetylacetonate as a New Type of Tin Compensator Additive for Tin-Based Perovskite Solar Cells

Tin (Sn)-based perovskite is one of the most promising candidates for lead (Pb)-free perovskite light-absorbing materials applied in solar cells. However, the intrinsic Sn vacancy (V_Sn) defects seriously hinder the device performance, making the reported maximum power efficiency (PCE) of Sn-based perovskite solar cells (PSCs) far behind those of Pb-based ones. During the study, SnF₂ has been demonstrated as an indispensable Sn compensator additive to improve the device performance. Considering that the default use of SnF₂ and the selection of a Sn compensator has also been limited to tin(II) halides, i.e., SnCl₂, SnBr₂, and SnI₂, the role and work mechanism of the Sn compensator have not yet been clarified clearly. Herein, a new type of Sn compensator, tin(II) acetylacetonate [Sn (acac)₂], is introduced into Sn-based PSCs. It is found that in addition to tin compensation, the organic ligand acac^- can coordinate with Sn²⁺ in the precursor solution and improve the crystallization process of perovskites. Consequently, the maximum PCE of formamidinium tin triiodide (FASnI₃) solar cells is enhanced from 3.88 to 7.27% using Sn (acac)₂ as the Sn compensator.