Dry-Spinnable Core-Sheath Carbon Nanotube Yarn(CSCNY) Electrode for Dye-Sensitized Solar Cell

Conventional fiber-shaped dye-sensitized solar cells (FDSSCs) employing platinum (Pt) as the counter electrode exhibit inadequate flexibility and face practical application constraints due to the elevated cost and unavailability of electrode materials. In this study, a novel core-sheath electrode covered with a carbon nanotubes film on the carbon nanotubes yarn(CNY) was proposed and implemented as the counter electrode(CE) of a flexible solid FDSSC.
Simple two-step mechanical reinforcement method was employed to fabricate core-sheath carbon nanotube yarn (CSCNY). Single CNYs(SCNYs) were fabricated by twisting the dry-spun CNT film. In the initial reinforcement, linear electrical resistance was enhanced by intertwining the seven strands of SCNYs into coiled-shape multi CNYs(MCNYs). In the final reinforcement, CNT film was applied to the surface of MCNYs to create mechanically stabilized and smoothly shape CSCNYs. Coiled MCNYs become untangled as soon as the tension sustaining elasticity decreases marginally. Following final reinforcement, CSCNYs maintained their coiled configuration despite being subjected to a tension-free condition. It is improbable for MCNY; the coiled structure disintegrated, resulting in a 23% increase in yarn length compared to its original state.
CSCNYs were utilized as an effective CE for FDSSCs. The CE serves as an electrode facilitating electron transfer from the photoactive electrode to the electrolyte, while also catalyzing the oxidation/reduction reactions of the electrolyte. In the final reinforcement, the coated CNT film smoothed the surface of the counter electrode and diminished the vacancies with the photoelectrode. The vacancy between the electrolyte and the electrodes' surface influences interface resistances regarding ion diffusion length for electron circulation. Electrochemical investigation utilizing electrical impedance spectroscopy revealed that CSCNY demonstrated the lowest charge transport resistance (RCE) of 13.8 ohms, confirming its effective electrocatalytic characteristics due to the core-sheath structure. In cyclic voltammetry analysis, CSCNY electrodes exhibited superior current values relative to Pt and other CNY electrodes, suggesting that CSCNY electrodes possess electrocatalytic properties that enhance the I-/I3-redox couple reaction, thereby improving the stability of solar cells. By enhancing the voltage and fill factor in the J-V characteristic, the CSCNY-based FDSSC attained a photoelectric conversion efficiency of 5.34%, reflecting an average performance improvement of 13.4% over the Pt-based FDSSC, which obtained a PCE of 5.06%
In the stretching-bending test, which preserves a high bending radius of 10 mm, CSCNY-based FDSSCs maintained efficiencies of 80% over 500 cycles, while being subjected to a high humidity environment for over 200 hours, demonstrating exceptional sustainability comparable to that of platinum electrodes. The FDSSC, based in CSCNY, has presented a wearable energy device capable of delivering stable electricity in conjunction with fabrics. These results indicate its potential as an effective electrode for a novel flexible FDSSC, serving as a substitute for Pt electrodes.