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.