Optimal TiO₂ Nanoparticles Electron Transporting Layer for Highly Efficient Ambient-atmosphere Fabricated Carbon-based Perovskite Solar Cells

The electron transporting layer (ETL) is a critical component for carbon-based planar Cs(0.17)FA(0.83)Pb(I0.83Br0.17)(3) perovskite solar cells (C-PSCs), as it facilitates efficient charge transport between the perovskite material and the cathode. The low temperature processed TiO2 nanoparticles (TiO2 NPs) ETL (150 degrees C) are widely employed in C-PSCs. However, the dispersion of commercial TiO2 NPs in colloid solution is often unstable, leading to particle agglomeration and sedimentation, which negatively affects the performance of C-PSCs. Therefore, it is crucial to achieve stable dispersion of TiO2 NPs in colloid solution before their application as ETL in C-PSCs. Furthermore, the surface properties of the TiO2 ETL such as the uniformity of film significantly impact the overall performance of C-PSCs. The objective of this study was to optimize the TiO2 ETL by investigating the dispersion of TiO2 NPs and varying their concentration in the solution for applying in ambient-atmosphere fabricated C-PSCs. The TiO2 NPs were dispersed in different solvents, including isopropanol, ethanol, and water. As a result, ethanol was the most effective solvent for dispersing TiO2 NPs, demonstrating the best dispersion stability. The concentration of TiO2 NPs in ethanol was then varied between 10-70 mg/ml. The results showed that the optimal concentration was 50 mg/ml, as it produced a high-quality ETL with a more uniform TiO2 film. This optimized TiO2 ETL in C-PSCs resulted in the highest power conversion efficiency (PCE) of 13.10% with FF, V-OC, and J(SC) values of 65.50%, 1.02 V, and 19.52 mA/cm(2), respectively.