Here we present the photovoltaic performance of solid-state dye-sensitized solar cells (DSCs) using a series of ullazine-based metal-free organic sensitizers and spiro-MeOTAD as a hole-transport material. A maximum of 4.95% power conversion efficiency measured under standard AM 1.5G illumination (100 mW cm2) was achieved with the best performing ullazine dye, and was further improved to 5.40% through co-sensitization with the triphenylamine-based organic sensitizer, D35. This study investigates the effect of the molecular structure of the ullazine sensitizer on the performance in solid-state DSCs.