Enhancing CsGeBr₃ perovskite: impact of Mn, V, and Cr doping on structural, optoelectronic, and thermoelectric properties

Abstract Perovskite materials have attracted increasing interest due to their excellent physical properties, making them particularly promising for various applications, such as optoelectronic and thermoelectric. In this paper, we investigate the effect of doping on the structural, electronic, optical, and thermoelectric properties of halogenated perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">CsGeBr</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:math> using density functional theory (DFT). Transition metals V, Cr, and Mn introduce doping at the B site. All materials retain a stable cubic structure. Doping introduces an intermediate band related to 3d states: this is located in the conduction band for V, reaches the Fermi level for Cr, and is below it for Mn. The band gap widens with V (1.64 eV) and Cr (1.49 eV), but decreases with Mn (0.74 eV). In the latter case, the appearance of an intermediate state strongly improves the absorption in the visible ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>α</mml:mi> <mml:msub> <mml:mrow> <mml:mfenced close=")" open="(" separators=""> <mml:mrow> <mml:mi>ω</mml:mi> </mml:mrow> </mml:mfenced> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>4.60</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mn>5</mml:mn> </mml:msup> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> ), which makes it promising for solar cells. In parallel, Cr and V improve the thermoelectric performance, with a high-power factor and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">ZT</mml:mi> </mml:math> figure of merit reaching 1 at 300 K in the n-type region. These modifications suggest that doping can effectively optimize the performance of perovskite-based optoelectronic and thermoelectric devices.