Correlation of elastic and optoelectronic properties near structural phase transition in organic-inorganic lead iodide perovskite single crystals.

The experimental evidence of the influence of the structural phase transition on the elastic and optoelectronic properties of CHNHPbIsingle crystals has been reported. A peak in the attenuation for longitudinal and shear ultrasonic waves and a step-like anomaly in their velocity have been found near the structural the orthorhombic-to-tetragonal phase transition (160 K). The narrow hysteresis observed in the temperature dependences of the elastic properties confirms that this is the first-order phase transition. A redshift of the absorption threshold (of about 110 meV) has been revealed both in the photocurrent (PC) and in the photoluminescence (PL) spectra with increasing temperature from 140 to 160 K. In the orthorhombic phase of CHNHPbIsingle crystals, the fine exciton structure in the PC spectrum has been found with an exciton binding energy of 19-25 meV. The peculiarities of the PC and PL spectra near the phase transition temperature (160 K) have been observed within a wider temperature range in contrast to the elastic anomalies that can be explained by the complex structure of the near-surface region. It may be essential for the further development of optoelectronic devices based on hybrid halide perovskites.