Degradation of Photovoltaic Devices at High Concentration by Space Charge Limited Currents

High-injection mobility reduction is examined by theory, modeling, and experimental data acquired by resonance-coupled photoconductive decay (RCPCD). The ambipolar mobility is shown to reduce to zero when the constituent injection-dependent carrier mobilities are taken into account. Modeling of the photoconductivity incorporating the transient, injection-dependent, ambipolar mobility confirms experimental reduction in signal at increasing carrier-generation rates. The onset of the reduction of mobility occurs at approximately 10 times the background carrier density; thus devices that utilize lightly doped materials are susceptible to anomalous injection-based behavior. For photovoltaic applications, high-injection device-performance degradation would result from mobility reduction due to reduced diffusion length.