High-Performance Dye-Sensitized Solar Cells through Graded Electron Transport in Band-Engineered W-TiO₂ Cascade Layer

The efficiency of TiO 2 -based dye-sensitized solar cells (DSSCs) has been limited because charge transfer is not fully achieved, and the injected electrons always recombine with the acceptor species before the electrode can collect them. The novel device architecture of offering graded bands into the TiO 2 photoanode network of DSSCs is presented to enhance the power conversion efficiency (PCE). Mono ( x %) as well as graded ( w–x–y–z %) W-doped TiO 2 films are prepared to form intermediate bands in the bandgap of TiO 2 . A significant enhancement in the PCE is achieved when mono x % W-TiO 2 films are tested as the photoanode of the DSSCs. Furthermore, DSSCs with band-engineered W-TiO 2 cascade layer exhibit significant photovoltaic performance showing graded carrier transport to current collector. In particular, a graded 1–5–7–9 W cascade film exhibits the highest photovoltaic performance of 11.30% without decreasing the open-circuit voltage, which is 48% higher than pristine DSSCs without a blocking layer. This graded carrier transport suggests an innovative route toward harvesting solar energy.