Three new thiazolo[5,4-d]thiazole-based organic dyes have been designed and synthesized for employment as DSSC sensitizers. Alternation of the electron poor thiazolothiazole unit with two propylenedioxythiophene (ProDOT) groups ensured very intense light absorption in the visible region (ε up to 9.41 × 10⁴ M⁻¹ cm⁻¹ in THF solution). The dyes were particularly suitable for application in transparent and opaque thin-layer DSSCs (TiO₂ thickness: 5.5–6.5 μm, efficiencies up to 7.71%), thus being good candidates for production of solar cells under simple fabrication conditions.