Comparing CV and DLCP Techniques in CIGS Solar Cells Through Self-Consistent Numerical Simulations

This study investigates the sensitivity of capacitance-voltage (CV) and drive-level capacitance profiling (DLCP) techniques to bulk and interface defect states in heterojunction solar cells using self-consistent numerical device simulations. In the presence of bulk and interface states, CV measurements on thin film solar cells often lead to misinterpretations of doping profiles. DLCP uses information from multiple AC test signal amplitudes and is nominally insensitive to interface states. CV, DLCP, and related techniques like admittance spectroscopy (AS) should all have different sensitivities to interface and bulk defects depending on the AC signal frequency, temperature, spatial and energetic distributions, and carrier capture and emission rates. Herein we utilize self-consistent numerical device physics simulations to characterize these sensitivities in a representative copper indium gallium diselenide (CIGS) thin film heterojunction solar cell. We investigate the sensitivity of CV and DLCP techniques under various scenarios of interface and bulk defects including changes in the density and spatial extent of near-interface states into the CIGS layer.