Pronounced excitonic effects in two-dimensional fullerene-based monolayer materials†

Two-dimensional (2D) fullerene monolayer materials exhibit a wide range of unique properties, including pronounced excitonic effects with significant potential for optoelectronic applications. Here, we perform a comprehensive investigation of the quasiparticle (QP) and excitonic properties of the C₂₀-2D monolayer using density functional theory (DFT) and many-body perturbation theory (MBPT) based on the GW approximation and Bethe–Salpeter equation (GW–BSE). Our calculations reveal substantial excitonic effects in the C₂₀-2D monolayer, with an impressive exciton binding energy of 1.58 eV, a notable breakthrough compared to the 0.8 eV reported for the C₆₀ monolayer. Embedding magnesium (Mg) into the C₂₀-2D monolayer induces polarization effects and enhances dielectric screening, driving a transition of the lowest-energy excitons from the Frenkel to the Wannier type. This transition is accompanied by significant changes in both the intensity and range of optical absorption. These findings reveal the tunability of fullerene materials through embedding, offering insights for the development of next-generation optoelectronic devices.