High-efficiency FTO-free counter electrodes for dye-sensitized solar cells based on low-Pt-doped carbon nanosheets

Highly efficient fluorine doped tin oxide (FTO)-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) are developed by a low amount doping of Pt on carbon nanosheet (CNS)-based charge-collecting electrodes. The low Pt-doped CNS-based CEs were prepared by simple deposition of Pt by a conventional method. The CNSs had a dual function as both highly conducting charge-collecting electrodes (sheet resistance of ∼40 ω/sq) and decent electrocatalytic CE layers for iodine reduction. Low Pt doping (using ∼100 times less Pt than with conventional doping) on a CNS dramatically improved the electrocatalytic activity for the I₃ reduction of the CNSs and the charge transfer resistance at CE/electrolyte interfaces, which was not possible using FTO. The performance of the low-Pt-doped CNS CEs was comparable to that of high (conventional)-Pt-doped FTO CEs. DSSCs using the low-Pt-doped CNS CEs showed a power conversion efficiency (PCE) of 7.56%, whereas those using high-Pt-doped CNS CEs showed a PCE of 8.05%. In contrast, DSSCs using low-Pt-doped FTO CEs showed a PCE of 4.50%, whereas those using high-Pt-doped FTO CEs showed a PCE of 8.21%. Pt/CNS is an intriguing CE material that can use 100 times less Pt than conventional Pt/FTO CEs, which suggests a useful strategy for reducing the fabrication cost of DSSCs.