Fountain pen ink possesses a well-dispersed nature and a relatively large specific surface area of carbon nanoparticles. In the present study, fountain pen ink was systematically studied and developed as cost-efficient counter electrodes (CEs) for planar dye-sensitized solar cells and fiber-shaped DSSCs (FDSSCs), which showed power conversion efficiencies above 6% under AM1.5G (100 mW cm⁻²). For ink-based planar solar cells, electrochemical impedance spectroscopy (EIS) confirmed that ink CEs had a slightly lower charge-transfer resistance than platinum CEs. EIS also proved that adding TiO₂ nanoparticles into the ink could reduce the device's series resistance and the diffusion impedance of the electrolyte through electrode pores. For ink-based FDSSCs, the effects of film thickness, light intensities, and a comparative research of CE catalytic activities toward various electrolytes were discussed.