Influence of caffeine on the crystallinity and thermal stability of MAPbI3: Experiment and density-functional theory calculations

Abstract

In this work, the effect of caffeine concentration (2 %, 4 %, 6 % and 8 %) on crystallinity and thermal stability of MAPbI3 was successfully studied. MAPbI3 showed stability at lower temperatures ranges between 0 and 90 °C, however, after adding caffeine the thermal stability showed an improvement towards higher temperatures [196–242 °C]. All the samples exhibited intense diffraction peaks at ∼2θ = 19.66° and 39.81°, respectively assigned to the (112) and (141) planes of tetragonal perovskite structure which indicates that the desired perovskite film was formed. MAPbI3@Caffeine (8 %) and MAPbI3@Caffeine (6 %) exhibited high PL intensity quenching which indicates their high charge carrier extraction efficacy which can be attributed to the higher crystallinity and fewer defect states of the film compared to MAPbI3@Caffeine (2 %) and MAPbI3@Caffeine (4 %) samples. MAPbI3@Caffeine (8 %) absorption spectra had the shifts to low wavelength in the range 491–532 nm which indicated that caffeine may allow sufficient photon into MAPbI3 due to the estimated bandgap. The density functional theory calculations suggest increased interactions at high caffeine concentration with corresponding switch from metallic to semiconducting properties. The stability of MAPbI3 can be attributed to increased cationic interaction between I 5p orbital states and C 2p, N 2p orbital states as indicated in the PDOS and electron density difference analysis.