Highly Dispersed Ligand-Free SnO₂ for Inverted Perovskite Solar Cells

Ligand-free SnO₂ nanoparticles were synthesized via a non-hydrolytic route using benzyl alcohol, resulting in well-crystallized SnO₂ with a size below 20 nm. The dispersibility of these SnO₂ nanoparticles was optimized using Hansen solubility parameters, achieving stable dispersion in a mixed solvent composed of isopropanol and chlorobenzene in a 2:8 volume ratio. The SnO₂ layer was deposited on the perovskite layer via spin-coating, forming a uniform and compact layer with efficient charge transfer properties. Photovoltaic performance analysis revealed that p-i-n perovskite solar cells with SnO₂ electron transport layer achieved a power conversion efficiency of 13.4%, compared to 15.8% for perovskite solar cells with PCBM/ZnO electron transport layer. The lower power conversion efficiency with SnO₂ electron transport layer is attributed to decreased open-circuit voltage (V_oc) due to surface defects. Despite this, the direct deposition of ligand-free SnO₂ thin film using a solution process is significant, and ongoing research aims to further enhance performance.