High-stability Ti4+ precursor for the TiO2 compact layer of dye-sensitized solar cells

•We developed an aqueous polymer-assisted deposition method to improve the chemical stability of the TiCl4 aqueous solution.•The Ti4+ is encapsulated by the polymer can maintain their initial performances for several months.•The film is dense, smooth and uniform, preparing by this method.•The power conversion efficiency of the DSSC based on P-TiO2 compact film is about 12.5% higher than that based on H-TiO2. A compact layer (blocking layer) can effectively block the direct contact between the fluorine-doped tin oxide (FTO) glass substrate and electrolyte in dye-sensitized solar cells (DSSCs). The TiCl4 hydrolysis has been widely adopted for preparing the TiO2 compact layer (H-TiO2). However, the TiCl4 aqueous solution is unstable for its high reactivity. To improve the chemical stability of TiCl4 aqueous solution, the Ti4+ is encapsulated by the polymer, polyethyleneimine (PEI). Experimentals show that the Ti-PEI precursor solution can maintain their initial performances for several months. The resulting TiO2 film (P-TiO2) grown by the Ti-PEI precursor is dense, smooth and uniform without any visible and detectable cracks or voids. The P-TiO2 compact layer is even denser than the H-TiO2 compact layer, suggesting reducing the electron recombination and prolonging the electron lifetime in dye-sensitized solar cells. Indeed, the electron lifetime of the DSSC based on the P-TiO2 is 13.15ms, which is longer than the 10.83ms based on H-TiO2. Meanwhile, the power conversion efficiency of the DSSC based on P-TiO2 compact film is about 12.5% higher than that based on H-TiO2. Therefore, this encapsulation technology can not only improve the stability of the metal ions solution but also meet a large-scale fabrication demand of the TiO2 compact layer in future DSSCs.