Spectroscopic investigation of the solvated MAPbI ₃ transition to perovskite crystals: a temperature-dependent Raman study

Hybrid organic-inorganic perovskites (HOIPs) have emerged as a transformative photovoltaic technology, achieving remarkable efficiency improvement in solar cell applications. However, the stability of perovskite-based materials remains a key issue and thus requires advanced non-destructive characterization methods. Raman spectroscopy, owing to its sensitivity to molecular and structural changes, is a promising tool for probing the surface characteristics of perovskite materials and for providing valuable insights into their vibrational properties and phase transition behavior. In this study, both <i>in situ</i> and <i>ex situ</i> Raman spectroscopy were employed to investigate the transition of solvated methylammonium iodide (MAI) and PbI₂ to MAPbI₃ perovskite crystals. The crystalline MAPbI₃ phase formed at 60 °C exhibited no distinct first-order Raman modes under 532 and 633 nm excitations, depicting its Raman inactivity under these conditions. Weak scattering features observed using a 785 nm laser can be attributed to the dynamic reorientation of methylammonium cations. These conclusions were supported by spectral measurements conducted under inert and atmospheric conditions at various power levels.