Heteroatomic molecules for coordination engineering towards advanced Pb-free Sn-based perovskite photovoltaics

As an ideal eco-friendly Pb-free optoelectronic material, Sn-based perovskites have made significant progress in the field of photovoltaics, and the highest power conversion efficiency (PCE) of Sn-based perovskite solar cells (PSCs) has been currently approaching 16%. In the course of development, various strategies have been proposed to improve the PCE and stability of Sn-based PSCs by solving the inherent problems of Sn²⁺, including high Lewis acidity and easy oxidation. Notably, the recent breakthrough comes from the development of heteroatomic coordination molecules to control the characteristics of Sn-based perovskites, which are considered to be vital for realizing efficient PSCs. In this review, the up-to-date advances in the design of heteroatomic molecules and their key functions in the fabrication of Sn-based perovskite films are comprehensively summarized. Firstly, the design principles of heteroatomic coordination molecules and their impact on the colloidal chemistry, crystallization dynamics, and defect properties of Sn-based perovskites are introduced. Then, state-of-the-art heteroatomic coordination molecules for efficient Sn-based PSCs are discussed in terms of their heteroatom types and functional groups. Lastly, we shed some light on the current challenges and future perspectives regarding the rational design of heteroatomic coordination molecules for further boosting the performance of Sn-based PSCs.