The nanoneedle-decorated shell, nanoneedle, and nanosheet structures of cobalt phosphide (named CoPNDS, CoP-N, and CoP-S, respectively) are synthesized via one-step hydrothermal method and phosphilization process. The CoP-NDS is consisted of nanoneedle with about 400 nm of length and nanosheet with about 100 nm of thickness. The CoP-NDS hierarchical structure provides a larger specific surface area and allows more electrolyte to penetrate into the interior of the nanospace. The result shows that dye-sensitized solar cell (DSSC) using CoP-NDS as the counter electrode (CE) exhibits the best photoelectric conversion efficiency (η) of 8.80 ± 0.07%, as compared to CoP-N (8.50 ± 0.13%) and CoP-S (7.71 ± 0.12%) CEs under the illumination of 1 sun (AM1.5G, 100 mW cm-2 ). Furthermore, CoP-NDS CE shows higher photovoltaic performance than traditional Platinum (Pt) CE (8.24 ± 0.02%), demonstrating its potential to replace Pt as CE in DSSCs. To further explore the application, the photovoltaic performance of DSSCs under dim light condition is also studied. The results show that DSSCs with CoP-NDS CE achieve η’s of 14.22 ± 0.12%, 15.75 ± 0.02%, and 17.27 ± 0.14% at 1000, 3500, and 7000 lux, respectively. This study concludes that the low-cost and easy-to-fabricate CoP-NDS can be a promising candidate to replace the conventional Pt CE in DSSCs.
Keywords Dim light photovoltaics, dye-sensitized solar cell, nanoneedle, nanosheet, Pt-free counter electrode, transition metal phosphide