Highly flexible and stretchable carbon nanotube network electrodes prepared by simple brush painting for cost-effective flexible organic solar cells

We developed highly flexible and transparent carbon nanotube (CNT) network electrodes prepared by a simple brush-painting method for the production of cost-effective flexible organic solar cells (FOSCs). By direct, rapid brush-painting of CNTs on a polyethylene terephthalate (PET) substrate using a conventional paintbrush made of nylon fibrils, we achieved percolated CNT network electrodes with a low sheet resistance of 286 Ω/square, a high diffusive transmittance of 78.45%, and superior mechanical flexibility at room temperature. The electrical, optical, and mechanical properties of the brush-painted CNT electrodes were investigated as a function of the number of repeated brush-painting cycles. In particular, brush-painted CNT electrodes showed outstanding flexibility in several test modes, including outer bending, inner bending, twisting and stretching, which are critical requirements in flexible electrodes. Notably, the brush-painted CNT network electrodes had a constant resistance change (ΔR/R₀) within outer and inner bending radii of 5 mm during dynamic fatigue testing. FOSCs fabricated on the brush-painted CNT electrode showed a power conversion efficiency of 1.632%, indicating the possibility of using brush-painted CNT electrodes as cost-effective flexible and transparent electrodes for printing-based low cost FOSCs.