Boosting photovoltaic efficiency in 2D cesium lead bromide perovskies via SnI₂ interlayer substitutional doping

In the field of optoelectronics, two-dimensional cesium lead bromide perovskites have emerged as a focal point of research, yet their application in photovoltaics is limited by a substantial bandgap and charge carrier confinement. To address this, our study introduces SnI₂ as a substitutional dopant within a monolayer of Cs₄Pb₃Br₁₀, yielding the novel composition Cs₄Pb₂SnI₂Br₈. This doped monolayer exhibits a direct bandgap reduced from 1.97 eV to 0.27 eV, extending the optical absorption spectrum. Using time-dependent density functional theory (TDDFT), we probed the electronic dynamics under ultrafast laser excitation, revealing enhanced photoresponse characteristics. The SnI₂ interlayer fosters carrier delocalization, amplifying the induced photocurrent, particularly under a 653 nm femtosecond laser with intensity from 1.327 × 10¹² to 1.327 × 10¹³ W/cm². Notably, the SnI₂ layers exhibit an intense long-range oscillating current peaking at ∼200 µA in the 4133 nm infrared regime. These unique optical response properties stem from interlayer excitons in the doped monolayer. This work outlines a strategic approach to enhance the photovoltaic efficacy of 2D cesium lead bromide perovskites and provides significant insights for designing advanced optoelectronic materials.