Design and synthesis of new processable materials for application in organic devices.

Abstract

New materials were designed and synthetized for photovoltaic applications featuring ability to be processed from green solvents including alcohol or water. In the synthesis of semiconductor materials, the well-known diketopyrrolopyrrole (DPP) unit was used as main building block for its features as excellent electron-acceptor unit in compounds with low bandgap. Six small molecules, based on DPP unit endcapped with triazolo group were synthetized and functionalized with solubilizing peripheral chains that allowed the dispersion in nonorganic and toxic solvents. All molecules were characterized through NMR and IR spectroscopy; in addition, physicochemical properties of the derivatives including solubility in variety of solvents, solution and film absorption and emission, and cyclic voltammetry (CV) were studied. Bulk heterojunction solar devices, using the synthetized materials as donors and PC60BM as acceptors were fabricated and tested. Furthermore, some polymers were designed to comprise DPP unit with polar triethylen glycol (Teg) side chains and different comonomers including vinyl, ethylhexyloxy benzodithiophene or functionalized thiophene ring. The majority of materials were synthesized using the Stille condensation reaction, but also an environmentally friendly process, the Direct Heteroarylation Polymerization (DAHP) reaction was profitably used. All materials were extensively characterized exhibiting low values of bandgaps and tested as donors in blends with PC70BM for photovoltaic response in both conventional and inverted device architectures, demonstrating, for the best polymer, a power conversion efficiency (PCE) around 1.5%. Interestingly, in field effect transistors, the same material, shows hole mobility approaching 0.015 cm2/Vs.