Novel Architecture of Indoor Bifacial Dye-Sensitized Solar Cells with Efficiencies Surpassing 25% and Efficiency Ratios Exceeding 95%

To prepare bifacial dye-sensitized solar cells (DSSCs), the classical photoelectrode employing the main light-absorbing layer (ML) and scattering layer (SL) will encounter the scattering effect of SL to the rear-side incident light and, thereby, decrease the rear-side efficiencies. To solve this problem, the SL has always been removed for the fabrication of bifacial cells. However, the front-side efficiency decreases without the SL. Here, a novel structure of a TiO₂ photoelectrode is developed for bifacial DSSCs to solve the contrary effect for cells with and without an SL, increasing both the front-side and rear-side efficiencies. This new structure is constructed by introducing an additional ML behind the SL of the traditional DSSC structure (ML/SL), creating a sandwich (ML/SL/ML) architecture of the TiO₂ film. The results demonstrate that rear illuminated light can be harvested more efficiently by this photoelectrode because the light is absorbed first by the last ML before suffering the effect of the SL. By using D35 and XY1b as cosensitizers of the photoelectrode, the front-side and rear-side efficiencies of the bifacial cells can achieve 25.04% and 23.7%, respectively, under 1000 lux fluorescent lighting, which means a rear-to-front efficiency ratio of 95%. The cells also show high efficiencies under one-sun conditions.