All-polymer solar cells based on Perylene-Diimide Copolymers: from material design to photovoltaic performances.

Polymer solar cells are attractive in view of their potential application for low-cost solar energy conversion. Polymeric solar cells generally consist of a bulk heterojunction made upon blending a light absorbing donor and hole-conducting conjugated polymer to an acceptor and electron-conducting material. The most successful acceptors to date are soluble fullerene derivatives that are characterised by good accepting properties and high electron mobilities. The replacement of fullerene by a polymer acceptor has raised the attention due to the potential advantages connected to the good absorption and to the easier tailoring of the electronic properties of conjugated polymer materials respect to fullerenes. However the difficulty in designing n-type polymers with good accepting properties and good electron mobilities to compete with fullerene is an issue that is limiting the power conversion efficiencies of all-polymer solar cells. In this contribution we present a series of acceptor perylene-diimmide copolymers with good accepting properties and good electron mobilities that we have designed and tested in all-polymer solar cells, in combination to poly-3-hexylthiophene. The solar cells exhibit encouraging power conversion efficiencies (1.6 %) and show remarkably good charge transport properties in the active blend, comparable to optimised polymer/fullerene devices.