Influence of interstitial Li on the electronic properties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>Li</mml:mi> <mml:mi>x</mml:mi> </mml:msub> <mml:msub> <mml:mi>CsPbI</mml:mi> <mml:mn>3</mml:mn> </mml

The integrated device of a perovskite solar cell with a Li-ion battery is an innovative solution for decentralized energy storage in smart electronic devices. In this study, we examine the stability of Li ions intercalated in a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>CsPbI</a:mi> <a:mn>3</a:mn> </a:msub> </a:math> perovskite and their effect on the electronic structure of <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mi>Li</b:mi> <b:mi>x</b:mi> </b:msub> <b:msub> <b:mi>CsPbI</b:mi> <b:mn>3</b:mn> </b:msub> </b:mrow> </b:math> compounds using first-principles density functional theory. Our simulations demonstrate that the insertion of Li at concentrations up to <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mi>x</c:mi> <c:mo>=</c:mo> <c:mn>1</c:mn> </c:math> into <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>CsPbI</d:mi> <d:mn>3</d:mn> </d:msub> </d:math> perovskite is energetically possible. Moreover, we identify that the distortion of the Pb-I octahedra has the strongest impact on the change in the electronic band gap. Specifically, an increase in the amount of intercalated Li causes larger structural distortions, which in turn lead to an increasing band gap as a function of the Li content.