Triplication of the photocurrent in dye solar cells by increasing the elongation of the π-conjugation in Zn-porphyrin sensitizers

Abstract

Porphyrins are promising sensitizers for dye solar cells (DSCs) but narrow absorption bands at 400-450 and 500-650 nm limit their light-harvesting properties. Increasing elongation of the π-conjugation and loss of symmetry causes broadening and a red-shift of the absorption bands, which considerably improves the performance of the DSC. Herein we use an oligothienylenevinylene to bridge a Zn-porphyrin system and the anchoring group of the sensitizer. We separately study the performance of the two basic units: oligothienylenevinylene and Zn-porphyrin. The combined system provides a three-fold enhancement of the photocurrent with respect to parent dyes. This is caused by an additional strong absorption in the region 400-650 nm that leads to flat IPCE of 60%. Theoretical calculations support that the addition of the oligothienylenevinylene unit as a linking bridge creates a charge transfer band that transforms a Zn-porphyrin dye into a push-pull type system with highly efficient charge injection properties