Structural, Photophysical, and Electronic Properties of CH₃NH₃PbCl₃ Single Crystals

Methylammonium lead chloride (CH₃NH₃PbCl₃ or MAPbCl₃) single crystals were fabricated using the inverse temperature crystallization method, and their structural, photophysical, and electronic characteristics were studied using temperature dependent optical spectroscopy, X-ray diffraction (XRD), current-voltage, and Hall measurements. The changes in absorption and photoluminescence properties accompanied with structural changes in crystal lattice were studied within a broad temperature range of 300-20 K. XRD investigations reveal that phase changes took placed around 180 K and 175 K. At a temperature below 170 K, two different crystallographic phases were found to co-exist in the photoluminescence spectra. An asymmetric line shape with broad and weak shoulders near the absorption edges was observed in all of the major PL peaks. The weak shoulders are attributed to the missing chloride atoms on the crystal surface. The photoluminescence intensity of the crystals was strongly influenced by the environment, thereby indicating that the carrier recombination is affected by the physical desorption/absorption of gas molecules at the crystal surface. Moreover, vibronic replicas in the photoluminescence spectra at low temperature were observed for the first time. The origins of these replicas are attributed to the coupling between the vibrational/librational motions of the organic cations and the photoexcited electrons. Finally, the Hall and current-voltage measurements confirm that the crystal is an n-type semiconductor with a carrier concentration of ~2.63 × 10¹¹ cm^-3, a mobility of 4.14 cm²/V•s, and a conductivity of 1.8 × 10^-8 Ω^-1 cm^-1 under dark and room temperature conditions.