Polymer solar cells based on macromolecular cascades

Organic solar cells hold promise as a sustainable energy source and for energy cost reduction. They represent a cost-efficient alternative to silicon-based cells. However, current technologies still require considerable molecular engineering work to solve problems related to the lifetime and improve the power conversion efficiency (PCE) of the photovoltaic devices. One methodology towards developing easy access to charge separated states is through the synthesis of new materials based on PPV type polymers, one with an acceptor character and the other one with a donor character linked through a transition metal complex or a series of transition metal complexes. The geometry of the desired architecture has been represented Scheme 1. Such a material presents the advantage of having a preferred path for the electrons and another one for the holes, allowing carrier generation by exciton dissociation. The transition metal complex extends the absorption range of the material due to its metal-to-ligand charge transfer (MLCT) transition around 500-600 nm and facilitates the charge carrier generation. The results so far have resulted in the synthesis, the photophysical and photovoltaic characterisation of new photoactive supramolecular dyads. An efficient energy-transfer process from the conjugated polymer block to the metal complex was shown. The coordination polymers were applied to photovoltaic using two types of devices: polymer solar cells and dye-sensitized solar cells (DSSCs). Promising results with efficiencies ~ 0.1 % were obtained for DSSCs, despite the absence of anchoring groups such as carboxylate. Polymer solar cells also displayed a photoresponse with very low efficiencies under illumination at 1000 W/m2 AM1.5. Their blend with porphyrin species to obtain an electron transfer from the porphyrin to the metal complex only resulted in a partial intermolecular energy transfer, justifying the necessity to have a covalent link between the two assemblies.