Oligothiophene cruciform with a germanium spiro center: a promising material for organic photovoltaics

Abstract

X marks the spot! A fascinating packing motif is observed in a novel cruciform oligothiophene containing a Ge (violet; see picture) spiro center. Long-range interchain interactions between molecules and strong electronic coherence between orthogonal chains within the molecules are present. Such ordering is advantageous for bulk charge transport, as demonstrated by high short-circuit currents in bulk heterojunction organic solar cells. Solution-processable bulk heterojunction (BHJ) solar cells offer a promising technology for solar energy conversion because of their low-cost fabrication, light weight, and potential use in large-area flexible devices. Most of the research in the field of organic photovoltaics (OPVs) has been focused on developing solar cells with a conjugated polymer (CP) as a donor compound. The ability of a polymer/fullerene acceptor blend to form a bicontinuous interpenetrating nanoscale network which provides efficient exciton dissociation and charge transport[1] has made polymeric donors the most promising materials for photovoltaic devices. At present the best solar cells with this type of donor exhibit power conversion efficiencies (PCE) of 8–9%,[2] which is close to the desired 10% PCE milestone.

Keywords Orthogonal chains, Molecules, high short-circuit currents, Organic solar cells