Toward Stable High-Performance Tin Halide Perovskite: First-Principles Insights into the Incorporation of Bivalent Dopants

Tin vacancy in CsSnI3 is a major issue that hinders halide perovskite solar cell performance stability and because of its increased p-type dopant concentration, changes its metallicity and hinders its recombination. To overcome this issue, we propose a bivalent dopant (i.e., Ca and Mn) in CsSnI3, acting as an electron donor. Here, we demonstrate by the first-principles study that bivalent dopants could boost CsSnI3 stability by their n-doped behavior and increased structural integrity. Ca and Mn substitution on α-CsSnI3 formation energy shows that these dopants will fill the vacancy position and prevent any tin vacancy formation in CsSnI3. In doped CsSnI3, the band gap was modulated by hybridization between the bivalent dopant and halide. The n-type behavior of the bivalent dopant shifts the Fermi level up, which will prevent self-p-doped behavior. Through the Shockley–Queisser equation, band gap modulation shows that the bivalent dopant increases solar cell performances. Our work shows that the bivalent dopant will stabilize and modulate the CsSnI3 structure to result in high-performance solar cells.