Design and coupling of multifunctional TiO₂ nanotube photonic crystal to nanocrystalline titania layer as semi-transparent photoanode for dye-sensitized solar cell

In order to conquer the challenges in the current technology to couple a dye-sensitized solar cell (DSSC) with a photonic crystal (PC), we propose a novel design of PC-based photoanode, composed of a thick TiO₂ nanoparticle absorption layer and a thin TiO₂ nanotube photonic crystal (TiO₂ NT PC) membrane. In this architecture, the bandgap of TiO₂ NT PC can be precisely tailored by modulating the anodization parameters using the current-pulse anodization process. Owing to the selective reflectivity of TiO₂ NT PC, the power conversion efficiency (PCE) of the electrodes reveals a strong wavelength dependence. Strategies to enhance the efficiency of the newly designed DSSC and its relation to the selective reflection of the photoanode are discussed and evaluated by experimental and simulated results. Meanwhile, the functionality of TiO₂ NT PC, offering both PC and light-scattering effects, has also been clarified. The combined effects of PC and light-scattering yield the maximum enhancement in PCE (39.5%) when the tailored TiO₂ NT PC, with the best matching of its reflectance maximum to the dye absorption maximum, is integrated into a DSSC. The work presented here provides new insights into the design and tailoring of a photonic crystal to enhance the PCE of DSSCs for practical applications.