Importance of Compact Blocking Layers to the Performance of Dye-Sensitized Solar Cells under Ambient Light Conditions

Power generation in indoor environments is the next step in dye-sensitized solar cell (DSSC) evolution. To achieve this goal, a critical recombination route which is usually inhibited by the TiCl₄-derived blocking layers (BLs), that is, charge transfer at the fluorine-doped tin oxide substrate/electrolyte interface, is of concern. In this study, we demonstrate that because of low surface coverage, the conventional TiCl₄ BLs are unable to suppress such electron leakage, thus limiting the photovoltaic performance of Co(bpy)₃^2+/3+-mediated DSSCs (bpy = 2,2'-bipyridine) under ambient lighting. On the other hand, by introducing compact BLs prepared by spray pyrolysis, the DSSCs show lower dark current and operate efficiently not only under high-intensity sunlight but also under ambient light conditions. The better blocking function of the compact BL is verified by the cyclic voltammetry; other thin-film preparation methods, except for the common TiCl₄ treatment, are anticipated to realize a similar blocking effect. This study illustrates that dense thin film with a predominant blocking function is highly required as the BL for DSSCs under low-light conditions, and this concept will pave the way for more development of indoor DSSCs.