Fabrication of Mesoporous Titania Nanoparticles with Controlled Porosity and Connectivity for Studying the Photovoltaic Properties in Perovskite Solar Cells

Mesoporous titania (TiO₂) nanoparticles (NPs) were synthesized by treating prehydrolyzed titanium precursors with polyethylene glycol (PEG). By varying the amount of PEG, their different physical properties were tuned appropriately in terms of surface area, pore size/volume, and electrical conductivity. By increasing the amount of PEG in TiO₂, the surface area and pore volume of mesoporous TiO₂ increased, and no direct correlation with the photovoltaic performance of perovskite solar cells was observed. In comparison, the pore size of mesoporous TiO₂ first increased greatly before quickly decreasing, and a similar trend was also observed for electrical conductivity. These implied that the interparticle interaction became much stronger with an optimum amount of PEG added to form mesoporous TiO₂ NPs_. With an optimum molar ratio of PEG/Ti precursor at 0.75, greatly improved conductivity of mesoporous TiO₂ NPs with interconnection as compared to that prepared in the absence of PEG, which was used as an electron transport layer, improved the power conversion efficiency of perovskite solar cells by ≈36%. Their greatly reduced photoluminescence after incorporating the perovskite also revealed a difference in the electron-injection properties from the perovskite into mesoporous TiO₂. This strategy highlights a versatile tool to tune mesoporous structures to achieve a cooperative effect for studying photovoltaic properties in perovskite solar cells.