Impact of capacitive effect on the J-V hysteresis in MgZnO/CdTe solar cells

Abstract

In this study, we demonstrate that the current–voltage (J-V) hysteresis of MgZnO (MZO)/CdTe solar cells mainly originates from the modification of J-V curves by nonsteady-state photocurrent, which is correlative with low-frequency capacitance corresponding to the MZO/CdTe interface. The hysteresis was significantly strengthened by introducing oxygen into the CdTe growth atmosphere, and became more pronounced as the MZO thickness increased. The electrical properties of MZO in CdTe solar cells were analyzed in detail by using thermomechanical lift-off technique. The results showed that oxygen during CdTe growth seriously deteriorated the conductivity of MZO by reducing the concentration of oxygen vacancy. Furthermore, a spike-like conduction band offset (CBO) greater than 0.25 eV was determined at MZO/CdTe interface due to the formation of Mg-rich surface layer. Thus, the low-frequency capacitance originating from electron accumulation at MZO/CdTe interface was increased due to the less probability of electron tunneling through the interface barrier. SCAPS simulations confirmed that the low-frequency capacitance was caused by substantially reduced conductivity of MZO and large CBO at MZO/CdTe interface. The experimental and simulation results indicate that the J-V hysteresis of MZO/CdTe cells can be suppressed by reducing low-frequency capacitance, which is achievable through enhanced electron transport at MZO/CdTe interface.