Synergism in carbon nanotubes and carbon-dots: counter electrode of a high-performance dye-sensitized solar cell

Dye-sensitized solar cells (DSSCs) play a crucial role in the realm of renewable energy technology by converting solar energy into electrical energy in an efficient and cost-effective way. In the pursuit of improving the photoconversion efficiency (PCE) of DSSCs, this work aims at fabricating a new counter electrode (CE) using a binary composite of heteroatom-doped carbon dots (C-dots) and functionalized multi-walled carbon nanotubes (o-MWCNTs). We demonstrate that this binary composite exhibits superior performance to pristine o-MWCNTs, resulting in a remarkable enhancement in the PCE. The PCE of the o-MWCNT/C-dots composite was measured at an impressive 4.28%, significantly outperforming the pristine o-MWCNT electrode, which yielded an efficiency of 2.24%. The enhanced performance of the o-MWCNT/C-dots composite can be attributed to the synergistic effects of heteroatom-doped C-dots since their binding to the o-MWCNTs by activated oxygenic surface functional groups increases the surface area from 218 to 253 m2 g-1. This enhanced surface area results from the reduction of pi-pi stacking interactions of the individual tubes and production of a new hollow channel in the structure that provides an ideal scaffold for I2 adsorption and electron transfer. We demonstrate the role of C-dots on MWCNT's property modulation toward higher PCE by density functional theory (DFT) calculation and electrochemical analysis. Electron-excess N and S doped C-dots exhibit strong catalytic activity, allowing for rapid electron transfer processes in the CE-electrolyte surface via the donor acceptor mechanism, whereas electron-deficient B doped C-dots undermine the cell performance by forming a charge recombination trap at the CE surface. The synthesized composite has higher redox reversibility up to 100 CV cycles and chemical stability, studied by the post-performance material characterization. The findings offer a promising avenue for the development of high-performance DSSCs, which will help to promote sustainable and renewable energy technologies. This study paves the way of tailoring property of counter electrode with carbon nanomaterials in dye-sensitized solar cell.