Two new metal-free organic sensitizers, L156 and L224, were designed, synthesized, and characterized for application in dye-sensitized solar cells (DSCs). The structures of the dyes contain a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid as electron-rich and -deficient moieties, respectively. Two different pi bridges, thiophene and 4,8-bis(4-hexylphenyl)benzo[1,2-b:4,5-b ']dithiophene, were used for L156 and L224, respectively. The influence of iodide/triiodide, Co(bpy)(3) (bpy=2,2 '-bipyridine), and Cu(tmby)(2) (tmby=4,4 ',6,6 '-tetramethyl-2,2 '-bipyridine) complexes as redox electrolytes and 18 NR-T and 30 NR-D transparent TiO2 films on the DSC device performance was investigated. The L156-based DSC with Cu(tmby)(2) complexes as the redox electrolyte resulted in the best performance of 9.26 % and a remarkably high open-circuit voltage value of 1.1 V (1.096 V), with a short-circuit current of 12.2 mA cm(-2) and a fill factor of 0.692, by using 30 NR-D TiO2 films. An efficiency of up to 21.9 % was achieved under a 1000 lx indoor light source, which proved that dye L156 was also an excellent candidate for indoor applications. The maximal monochromatic incident-photon-to-current conversion efficiency of L156-30 NR-D reached up to 70 %.