We have designed and synthesized highly efficient organic sensitizers with a planar thienothiophene–vinylene–thienothiophene linker. Under standard global AM 1.5 solar conditions, the JK-113-sensitized cell gave a short circuit photocurrent density (Jsc) of 17.61 mA cm−2, an open-circuit voltage (Voc) of 0.71 V, and a fill factor (FF) of 72 %, corresponding to an overall conversion efficiency (η) of 9.1 %. The incident monochromatic photo-to-current conversion efficiency (IPCE) of JK-113 exceeds 80 % over the spectral region from 400 to 640 nm, reaching its maximum of 93 % at 475 nm. The band tails off toward 770 nm, contributing to the broad spectral light harvesting. Solar-cell devices based on the sensitizer JK-113 in conjunction with a volatile electrolyte and a solvent-free ionic liquid electrolyte gave high conversion efficiencies of 9.1 % and 7.9 %, respectively. The JK-113-based solar cell fabricated using a solvent-free ionic liquid electrolyte showed excellent stability under light soaking at 60 °C for 1000 h.