Bifacial light-harvesting technology is regarded as one effective strategy to enhance the power output of photovoltaic devices, in which the transparent electrode is crucial to determine the power conversion efficiency when illuminated from rear side. To date, the efficiency enhancement of the state-of-the-art bifacial mesoscopic solar cells is mainly focused on the rational design of high catalytic counter electrode without sacrificing the transparency. The cell performance maximum through increasing electron density at counter electrode surface to enhance its catalytic ability is still a challenging problem. In the current work, bi-tandem carbon quantum dots are made to tailor transparent CoSe counter electrode for bifacial dye-sensitized solar cells, achieving a maximized front power conversion efficiency of 8.54% and a rear efficiency of 6.55% in comparison with 7.87% and 5.03% for carbon quantum dots-free device, respectively. The mechanism behind this increment is stemmed from the photo-excited electrons of bitandem carbon quantum dots and therefore realizing the electron accumulation on the counter electrode surface. (C) 2018 Elsevier Ltd. All rights reserved.