Structural and Functional Analysis of Caffeine Doped Perovskite Single Crystal: Insights into Molecular Organisation and Performance

The structural quality and stability of methylammonium lead iodide (MAPbI 3 ) single crystals play a crucial role in determining their suitability for optoelectronic applications. In this study, caffeine, a carbonyl-rich organic molecule capable of interacting with undercoordinated Pb 2+ ions, was employed as an additive during the growth of MAPbI 3 single crystals using the inverse temperature crystallisation (ITC) method. The influence of caffeine on crystal growth, structural properties, molecular interactions, and thermal stability was investigated using powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). XRD analysis confirmed the formation of highly crystalline MAPbI 3 with enhanced phase purity, suggesting improved crystallinity in the presence of caffeine, indicating its role in regulating crystal growth and suppressing the formation of undesirable secondary phases. FTIR spectroscopy revealed characteristic vibrational features associated with both MAPbI 3 and caffeine, suggesting favourable interactions between the additive and the perovskite lattice. TGA measurements demonstrated that the caffeine-modified crystals possess good thermal stability and retain their structural integrity over the investigated temperature range. Furthermore, caffeine incorporation facilitated the growth of larger, well-defined single crystals with improved structural characteristics. The combined results indicate that caffeine-assisted crystallisation is an effective strategy for improving the quality and stability of MAPbI 3 single crystals. These findings provide valuable insights into additive-mediated crystal growth and highlight the potential of caffeine-modified perovskites for future high-performance optoelectronic applications.