Thiazole-based scaffolding for high performance solar cells

An interesting way of decreasing both HOMO and LUMO energy levels simultaneously while keeping the band-gap constant in soluble electron-donor small molecules for photovoltaic applications is presented. This consists in the replacement of thiophene rings by thiazole units in small molecules based on the alternation of electron-rich and electron-deficient moieties. A new diketopyrrolopyrrole-based dumbbell-shaped electron-donor soluble molecule for organic photovoltaic applications has been synthesized and characterized. It includes thiazole units as linkers between the bis-lactam core and the triazatruxene moieties used as π-stacking platforms. A power conversion efficiency of 6.3% has been attained with this thiazole derivative and in particular with an increase of the open-circuit voltage of 0.15 V with respect to the thiophene-based organic semiconducting counterpart. This open-circuit voltage increase is due to the lowering of the HOMO level of the thiazole derivative while its LUMO level has also been stabilized as highlighted by the similar band-gap measured for the thiazole and thiophene derivatives.