Phono-voltaics and optical phonon harvesting in nanoscale Hg1−xCdxTe <i>p–n</i> junctions: Predictions and insights from first-principles DFT + NEGF + STD investigations

The recently proposed concept of phono-voltaics enables electron–hole pair generation in nanoscale p–n junctions through the harvesting of non-equilibrium optical phonons. Using a density functional theory (DFT) + non-equilibrium Green's function (NEGF) + special thermal displacement (STD) framework, we demonstrate that Hg1−xCdxTe, with tunable Cd concentration, offers a versatile platform for designing nanoscale junctions suitable for both phono-voltaic and photo-voltaic applications. In the phono-voltaic regime, carrier generation arises from electron–phonon coupling (EPC) when the optical phonon energy matches or exceeds the bandgap. Our results also highlight the critical role of EPC in predicting photovoltaic performance at room and elevated temperatures. We further show that essential parameters, such as temperature-dependent bandgap shifts, optical absorption, phono-current, photocurrent, and open-circuit voltage (VOC), can be reliably obtained from first-principles DFT + NEGF + STD calculations, providing insights for the design of next-generation nanoscale energy-harvesting devices.