On the Adsorption Mechanism of Caffeine on MAPbI3 Perovskite Surfaces: A Combined UMC--DFT Study

Recently, it was experimentally shown that the performance and thermal stability of the perovskite MAPbI$_3$ were improved upon the adsorption of a molecular layer of caffeine. In this work, we used a hybrid methodology that combines Uncoupled Monte Carlo (UMC) and Density Functional Theory (DFT) simulations to carry out a detailed and comprehensive study of the adsorption mechanism of a caffeine molecule on the surface of MAPbI$_3$. Our results showed that the adsorption distance and energy of a caffeine molecule on the MAPbI$_3$ surface are 2.0 \r{A} and -0.3 eV, respectively. The caffeine/MAPbI$_3$ complex presents a direct bandgap of 2.38 eV with two flat intragap bands distanced 1.15 and 2.18 eV from the top of valence bands. Although the energy band levels are not significantly shifted by the presence of caffeine, the interaction MAPbI$_3$/perovskite is enough to affect the bands' dispersion, particularly the conduction bands.