Dye-sensitized solar cells (DSSCs) have attracted remarkable attention due to their high efficiency, environmentally friendly, and low cost. The counter electrode (CE) catalysts as an indispensable part play a crucial role in DSSCs. Herein, the novel tantalum-based bimetallic oxides (FeTa2O6, CoTa2O6, and CuTai(10)O(26)) and bio-based spherical carbon (SC) supported composites (FeTa2O6/SC, CoTa2O6/SC, and CuTai(10)O(26)/SC) were prepared successfully through a hydrothermal/annealing process, which were used as CEs catalysts for DSSCs. The bio-based SCs were obtained through hydrothermal carbonization of aloe peel waste. Of them, the FeTa2O6/SC, CoTa2O6/SC, and CuTai(10)O(26)/SC CEs catalysts exhibited excellent electrocatalytic activities and electrocatalytic stability for I-3(-) reduction, thus resulted in comparable power conversion efficiency (PCE) of 6.85%, 6.79%, and 6.53% to Pt-based CE (6.34%) in DSSCs. This work will open new research opportunities for the use of transition metal compounds (TMCs) in renewable energy fields. (C) 2019 Elsevier Ltd. All rights reserved.