Influence of Adjustable CeO2 Morphology on the Performance of Ambient Hole Transport Layer-Free Carbon-Based Perovskite Solar Cells

The combined effect of TiO₂ and CeO₂ as the electron transport layer (ETL) in the hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) to enhance performance characteristics is a less explored research area. In this context, we investigated the effect of morphology-tuned CeO₂ in combination with TiO₂ in the C-PSCs. Considering the light scattering effect in C-PSCs and the property of extending the light-traveling distance across the photoelectrode, we synthesized rod and cubic CeO₂ nanostructures. The synthesized nanoparticles were used over the TiO₂ layer, and their photovoltaic performance was compared to that of the TiO₂-only C-PSC and analyzed by using impedance and quantum efficiency studies. The light-scattering effect on the C-PSCs, investigated with the diffused reflectance study, found that the rod structure of CeO₂ provides better light travel toward the photosensitizer, and the highest power conversion efficiency (PCE) of nearly 12.5% was recorded for the rod-shaped CeO₂ in the HTL-free C-PSC, which is 24% higher compared to a pristine TiO₂-based C-PSC. Moreover, the devices with rod-shaped CeO₂ demonstrated suitable charge transport properties along the perovskite layer and a lower charge recombination rate when compared with the cube structure. This work demonstrates a major breakthrough in the performance enhancement of HTL-free C-PSCs by nanomaterial morphology alteration and fabrication engineering, which can significantly influence future research.