Zirconia Spacer Optimization for Improved Performance in HTL-Free Mesoscopic Perovskite Solar Cells with Carbon Electrode

This study focuses on optimizing the spacer layer in mesoscopic perovskite solar cells (MSPSCs) to enhance their performance, specifically in cells using a carbon electrode without hole transport layers (namely HTL-free). Two variations of zirconia-based spacers were investigated: ZrNanoxide ZT/SP and Zr-Nanoxide Z/SP. The photovoltaic measurements demonstrated that MSPSCs with the $\mathbf{Z r}$ Nanoxide ZT/SP spacer achieved a significantly higher power conversion efficiency (PCE) of 1.42%, compared to 0.42% for cells using the Zr -Nanoxide $\mathrm{Z} / \mathbf{S P}$ spacer. The enhanced performance of $\mathbf{Z r}$-Nanoxide ZT/SP was attributed to its favourable surface morphology and small particle size, as evidenced by DektakXT profilometry and scanning electron microscopy (SEM) analysis. These findings underscore the critical urgency of spacer selection in optimizing the efficiency of MSPSCs, with Zr-Nanoxide ZT/SP emerging as the more effective material for boosting cell performance.