Improving the Performance of Carbon-Based Perovskite Solar Cells by the Incorporation of a Screen-Printed NiCo₂O₄...

Hybrid lead halide perovskite solar cells (PSCs) stand out in terms of their high efficiency, yet the limited stability and process scalability pose challenges to their commercialization. Fully printable carbon-based perovskite solar cells (C-PSCs), consisting of a triple stack of mesoporous titania, zirconia, and carbon layers impregnated with the perovskite material, have been introduced as an attractive architecture; however, they generally exhibit lower efficiency. This study proposes a viable and scalable approach to increase the efficiency of C-PSCs by incorporation of an intermediate layer of mesoporous, nanostructured NiCo₂O₄ between the zirconia and carbon layers. The devices show an average increase in power conversion efficiency from 7.9 to 11%, with a champion device efficiency of 12.4%, associated with an enhanced average open-circuit voltage (V _OC) from 0.869 to 0.962 V. Electrochemical impedance spectroscopy reveals that the high-frequency recombination resistance (R _HF) decreases exponentially with V _OC with the same slope as for the reference triple-stack system, indicating that the mechanism is unchanged; however, a substantial increase in R _HF is observed. These results indicate that the hole extraction efficiency improves upon incorporation of the NiCo₂O₄ film thus decreasing surface recombination at the nonselective carbon contact. On the other hand, we postulate a possible contribution of the high capacitance of the interlayer, which may result in a shift of the Fermi energy of the carbon electrode and play a role in the hysteresis in the current - voltage curve.