A delafossite CuCrO₂hole transport layer deposited at room temperature from a nanoparticle suspension is used in efficient perovskite cells.

Using capacitance-frequency ($C\text{−}f$) analysis to characterize the density-of-states (DOS) distribution of defects has been well established for inorganic thin-film photovoltaic devices. While $C\text{−}f$ analysis has also been applied to bulk-heterojunction (BHJ) organic photovoltaic (OPV) devices, we show that the low carrier mobility in the BHJ material can severely alter the $C\text{−}f$ behaviors and lead to misinterpretations. Because of the complicated nature of disorders in organic materials, artifacts from an erroneous $C\text{−}f$ analysis are difficult to identify. Here we compare drift-diffusion simulations with experiments to reveal situations when the validity of $C\text{−}f$ analysis for defect characterization breaks down. When a flat-band region is present in the low-mobility active layer, the capacitive response cannot follow the electrical modulation and behaves as if the active layer is a dielectric at frequencies higher than the characteristic frequency determined by carrier mobility and thickness. The transition produces a fictitious shallow defect when defect analysis is applied. Even in fully depleted devices, the defect distributions derived from $C\text{−}f$ analysis can appear at spuriously deeper energies if the mobility is too low. Through simulations, we determine the ranges of mobility and thickness for which the $C\text{−}f$ analysis can effectively yield credible defect DOS information. Insight from this study also sheds light on transport limitation when using capacitance spectroscopy for defect characterization in general.