How single-crystal charge carriers could improve solar cells

Emerging solar-cell technologies got a boost last year thanks in part to Osman M. Bakr and his team at King Abdullah University of Science & Technology when the researchers developed single crystals of light-harvesting materials. The researchers are now double-dipping in their single-crystal strategy to try and further improve photovoltaics by turning their attention to a different component of the solar-cell anatomy: hole-transport materials. These materials conduct electrically positive charge carriers, known as holes, in both perovskite and dye-sensitized solar cells (see page 30). The most popular hole-transport materials are amorphous thin films prepared from a polyaromatic molecule called spiro-OMeTAD, Bakr says. His team created single crystals of spiro-OMeTAD by dissolving it in dimethyl sulfoxide and then slowly exposing the solution to vapors of an antisolvent, methanol, to coax crystallization (Sci. Adv. 2016, DOI: 10.1126/sciadv.1501491). This approach allowed the researchers to report the crystal structure of spiro-OMeTAD for the first time, they say. The team further showed that the molecular packaging within a crystal allows the material to conduct holes far better than amorphous thin films currently in use.