Dye-sensitized solar cells (DSSCs), invented by Michael Grätzel and Brian O’Regan in 1991, are recognized as a cost-efficient alternative to traditional photovoltaic cells. Typically, they are based on n-type semiconductors (e.g. TiO2) as the anode where the light energy is harvested. More recently, researchers have introduced the reverse type of solar cell, where p-type semiconductors (e.g. NiO) act as a light-harvesting cathode. N- and p-type semiconductors are doped with small amounts of negative or positive charge carriers, respectively. In DSSCs, the organic dye molecule takes over the function of doping, injecting electrons or holes, respectively, into the semiconductor material.
Now the group of Licheng Sun and Anders Hagfeldt at the Royal Institute of Technology at Stockholm , Sweden , have more than doubled the efficiency of p-type semiconductor DSSCs, opening up the prospect of using them in tandem with the traditional Grätzel cell, i.e. in an arrangement where both electrodes contribute to the conversion of solar energy.
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