Efficiency Enhancement in ZnO:Al-Based Dye-Sensitized Solar Cells Structured with Sputtered TiO2 Blocking Layers

We explored new strategies for efficiency enhancement in dye-sensitized solar cells (DSSCs) by combining dehydration−condensation reactions with sputtering deposition methods. The photoanodes were realized by means of low-temperature preparation of mesoporous TiO2 films on thin undoped TiO2 compact (blocking) layers on ZnO:Al (AZO) substrates and sensitization with ruthenium dye, N719. For photoanodes fabrication, an 8 μm thick mesoporous film of TiO2 and an under critical thermal budget, applied before dye loading (≤200 °C: i.e., 150 °C for the TiO2 mesoscopic layer and 200 °C for the TiO2 blocking/AZO bilayer), were employed, which renders the overall process competitive for the applications. The structural properties of the sputtered TiO2/AZO bilayer were optimized, and a cell efficiency as high as the 4.6%, above the current literature limit for AZO-based DSSC (3.8% for 10 μm thick mesoporous layers sintered at 450 °C and sensitized with N719), was achieved at T ≤ 200 °C. With the proposed scheme for the photoanode structure and using, instead, a conventional thermal treatment at 500 °C (30 s), the cell efficiencies were further raised up to 4.9%. It was thus evidenced that the use of optimized materials for the cell architecture makes the AZO-based DSSC nowadays rising devices.