Crystal Pre‐Dissolved Method Fabricates Diverse Phase‐Pure Q‐2D and FA‐3D Tin‐Based Perovskite Heterojunctions

Compared with 3D lead halide perovskites, tin‐based ones (especially that composed of MA cation, MA‐3D), have many merits, including eco‐friendly characters and superior optoelectronic properties. However, its stability and repeatability remain great concerns compared with the FA cation‐based one (FA‐3D). Quasi‐2D (Q‐2D) tin‐based perovskites surpass the 3D counterpart in this aspect; nevertheless, the fabrication of those phase‐pure films is still challenging due to similar formation energies of different n values, thus making their photovoltaic device performance inferior to 3D analogs. Here, we intentionally designed, fabricated, and systematically studied diverse phase‐pure Q‐2D/3D heterogeneous tin‐based perovskites for enhancing the optoelectronic performance. Exploiting the developed temperature‐lowering method with pre‐synthesized polycrystalline materials, we successfully fabricated bulk crystals of 3D and Q‐2D tin‐based perovskites. With these crystals, we prepared highly pure and stable precursor solutions, which are used for producing Q‐2D tin perovskite films with a determined n value, aligned growth orientation, and enhanced stability. Furthermore, we fabricated phase‐pure Q‐2D/FA‐3D heterojunctions for optoelectronic properties, which benefit for achieving low‐cost heterojunction solar devices with boosted PCE, outstanding repeatability, and long‐term stability, thus providing an avenue for the development of MA‐based tin perovskite devices.