Computational and experimental investigation of the structure, morphology, optical and electrical properties of TiO2 and caffeine adsorbed TiO2 in methyl ammonium lead iodide

Abstract

Effects of caffeine and titanium dioxide (TiO2) in methylammonium lead iodide (MAPbI3/CH3NH3PbI3) as a photon absorber are studied. XRD showed high crystallinity of TiO2:Caffeine:MAPbI3 with larger crystallite size of ∼3.9 nm compared to TiO2:MAPbI3 with ∼3.6 nm. Large grain size of ∼550 µm was obtained for TiO2:Caffeine:MAPbI3 compared to ∼256 µm of TiO2:MAPbI3. Rod-like structures were observed though TiO2:Caffeine:MAPbI3 morphology and was smoother compared to TiO2:MAPbI3. Reduced bandgap energy of ∼2.3 eV was observed from TiO2:Caffeine:MAPbI3 and PL quenching indicated the possibility of reduction of the electron-hole recombination. TiO2:Caffeine:MAPbI3 showed better electrical conductivity compared to TiO2:MAPbI3. Density functional theory calculations showed increased charge transfer/redistribution which accounts for the slight enhanced electrical conductivity for TiO2:Caffeine:MAPbI3. The density of state calculations suggests the formation of unoccupied states and O 2p, Ti 3p, N 2p and C 2p as major contributors to the electronic and electrical properties of TiO2:Caffeine.