2026 Sandberg Undoped Thin Film Diode Capacitance

The capacitance of thin-film diodes based on undoped semiconductors is predominantly influenced by injected charge carriers rather than doping-induced carriers, yet an analytical framework for understanding this capacitance has been lacking. This study aims to derive a comprehensive analytical description of the capacitance that fully incorporates both injected charge carrier effects and electrode charge interactions. Furthermore, a method for extracting the built-in voltage of these devices is presented. The theoretical foundation established is validated through numerical simulations employing a drift-diffusion model, as well as experimental data collected from organic solar cells. The significance of the built-in potential is underscored as it serves as a driving force in charge extraction within photovoltaic devices and plays a crucial role in determining the injection threshold in light-emitting diodes. While capacitance-voltage (C-V) measurements have typically been utilized to ascertain the built-in voltage, conventional Mott-Schottky analysis proves inadequate for devices with thin active layers or low doping levels, thereby necessitating the model developed in this study. This analytical framework not only provides insights into capacitance behavior in thin-film diodes but also enhances the understanding of their operational characteristics in emerging applications.