The effect of B-site alloying on the electronic and opto-electronic properties of RbPbI3: A DFT study

TL;DR

This study uses density functional theory to explore how alloying the B-site in RbPbI3 with Sn and Ge affects its structural, electronic, and optical properties, aiming to improve perovskite solar cell performance.

Contribution

It provides a comprehensive analysis of the stability, bandgap tuning, and efficiency potential of RbPbI3 with B-site alloying using DFT, which was not extensively reported before.

Findings

Alloying reduces the bandgap, with the lowest at 1.85 eV for RbPb{1-x}GexI3 at x=0.50.

Maximum spectroscopic limited maximum efficiency (SLME) of 23% achieved with equal Sn/Ge and Pb admixture.

The exciton type shifts from Mott-Wannier to Frenkel with increasing Sn/Ge content.

Abstract

Divalent cations mixed lead halide perovskites with enhanced performances, high stabilities, and reduced toxicity are requisite to make persistent progress in perovskite solar cells. However, the mixing strategy is not reported extensively in search of a lead reduced structure. Herein, we report the structural, electronic and optical properties of RbPb{1-x}MxI3 (where, M={Sn,Ge} and x={0.25, 0.50, 0.75}) by alloying the B-site with Sn and Ge, using the density functional theory. The formation enthalpy is estimated for all RbPb{1-x}MxI3 (with x= 0.25, 0.50, 0.75), which confirms stability for all the structures. The energy bandgap and density of states (DOS) have been thoroughly investigated. The energy bandgap decreases with the increasing Sn/Ge contents, the lowest bandgap of 1.850 eV is observed at x = 0.50 in the case of RbPb{1-x}GexI3 systems. Further, the effective masses and the binding energy of excitons and spectroscopic limited maximum efficiency (SLME) are also estimated for all the mixed systems. The exciton type is observed to change from Mott-Wannier to Frenkel type with increasing the contents of both Sn and Ge at the B-site. The maximum efficiency of 23% is achieved using an active layer containing an equal admixture of Sn/Ge and Pb. The estimated parameters of both the mixed systems are consistent with the available literature of similar types.