Organic and Hybrid Solar Cells

The quest for clean and sustainable energy sources drives the development of solar cell technology. Organic photovoltaics (OPV) and dye-sensitized solar cells (DSCs) are attractive for low cost, large area applications. OPV offer the further advantages of mechanical flexibility and transparency. However, the relatively low efficiency of OPV and DSCs, compared to inorganic devices, leaves much to be desired. In both OPV and DSCs sunlight is harvested by organic (or metal-organic) species and charge separation is driven by the potential energy difference at an interface. In OPV it is an organic-organic interface between donor and acceptor species, while in DSCs it is an organic-inorganic interface between a dye and an oxide (typically TiO2). Understanding, predicting, and controlling the structure and electronic properties of the functional nanostructured interfaces in the active region is the key to increasing the efficiency of OPV and DSCs. We seek insight from first principles that will lead to design rules for more efficient solar cells.

Singlet fission (SF), the conversion of one singlet exciton into two triplet excitons, may lead to the realization of high efficiency organic photovoltaics by generating two carriers from one photon. Recently, SF has been observed in the orthorhombic form of rubrene. We use many-body perturbation theory in the GW approximation and the Bethe-Salpeter equation (see also: Electronic Excitations) to show that crystal packing significantly affects the electronic and excitonic properties of rubrene. Based on our calculations, the triclinic form and, to a greater extent, the monoclinic form of rubrene, are expected to exhibit higher SF efficiencies than the orthorhombic form. CrystEngComm DOI: 10.1039/c6ce00873a (2016)

Size effects in the interface level alignment between catechol and increasingly large TiO2 clusters. The interface level alignment is determined by the interplay of quantum confinement and dynamic screening. J. Phys. Chem. Lett. 5 2395 (2014)