Interstitial Mn²⁺-Driven High-Aspect-Ratio Grain Growth for Low-Trap-Density Microcrystalline Films for Record Efficiency CsPbI₂Br Solar Cells

It is imperative to develop a large-aspect-ratio grain-based thin film with low trap density for high-performance inorganic perovskite CsPbI₂Br solar cells. Herein, by using Mn²⁺ ion doping to modulate film growth, we achieved CsPbI₂Br grains with aspect ratios as high as 8. It is found that Mn²⁺ ions insert into the interstices of the CsPbI₂Br lattice during the growth process, leading to suppressed nucleation and a decreased growth rate. The combination aids in the achievement of larger CsPbI₂Br crystalline grains for increased J_SC values as high as 14.37 mA/cm² and FFs as large as 80.0%. Moreover, excess Mn²⁺ ions passivate the grain boundary and surface defects, resulting in effectively decreased recombination loss with improved hole extraction efficiency, which enhances the built-in electric field and hence increases V_OC to 1.172 V. As a result, the champion device achieves stabilized efficiency as high as 13.47%, improved by 13% compared with only 11.88% for the reference device.