Thermal Stability of Organic Semiconductor Thin Film Glasses by Local Changes in Spontaneous Orientation Polarization

Vapor-deposited organic semiconductor glasses exhibit distinct molecular anisotropy and exceptional kinetic and thermodynamic stability, distinguishing them from the inherently isotropic and poorly stable glasses formed through liquid cooling. In this study, we exploit these unique properties to examine local changes in surface potential as the stable glass transitions to a supercooled liquid upon heating above the glass transition temperature (T_g). Vapor deposited glasses of organic molecules with permanent dipole moments can generate a measurable surface potential due to their anisotropic molecular orientation. We use local electrostatic force microscopy and Kelvin probe force microscopy to provide insights into the dynamics of the phase transformation occurring above T_g. We demonstrate that changes in polarization upon conversion to the isotropic liquid serve as an effective proxy for tracking this transition and highlight their potential for evaluating the thermal stability of organic devices under diverse thermal conditions.