Heat capacity and thermodynamic functions of di-,tri- and tetramethylammonium lead iodide perovskites from 289 to 473 K

The heat capacity of di-, tri- and tetramethylammonium lead iodide perovskites of general formula (CH3)xNH4–xPbI3 (where 2≤x≤4) has been determined by differential scanning calorimetry (DSC) in the temperature range 289–473 K using the step-scan mode. Standard molar values C0p(298 K) of di-, tri- and tetramethylammonium lead iodide perovskites were found to be: (285.2, 318.8 and 363.4) J K–1 mol–1, respectively. Heat capacity data have been used to evaluate the thermodynamic functions of the three (CH3)xNH4–xPbI3 perovskites (entropy and enthalpy increment). Further DSC experiments were carried out simultaneously with thermogravimetry (TG) at constant heating rate (4 K min–1) to study the thermal behavior. The occurrence of a phase transition was detected in two of the three perovskites in well-defined temperature ranges and the corresponding transition temperatures (taken as the onset temperatures of the DSC peaks) resulted to be 346.6 K and 353.5 K for (CH3)3NHPbI3 and (CH3)4NPbI3, respectively. The three powder samples were also characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses.