Toray Industries Inc has announced a polymer organic thin-film photovoltaic (OPV) cell that is claimed to have world’s highest level of power conversion efficiency of 10.6%.
In construction of the solar cell Toray researchers used a material they have named “Polymer-1” – a thiophene-based polymer material developed by the company – as an electron donor (the equivalent of the p-type semiconductor of inorganic semiconductor). Also the device uses “PCBM70” – which is a C70 derivative – as an electron acceptor (n-type semiconductor).
The HOMO (highest occupied molecular orbital) level and band gap of the Polymer-1 are -5.1eV and 1.58eV, respectively. Its carrier mobility is about 1.0 x 10-2cm2/Vs, which is higher than that of the electron donor material that Toray previously used.
The Toray researchers initially made a 4mm2 OPV cell whose active layer film was just 130nm thick by using Polymer-1 and it produced a power conversion efficiency of 9.4%. Next the researcher made similar size OPV cells but this time they increased the active layer thickness to 300mm with the aim to achieve higher light absorption. What the researchers found was that absorption rates increased for short-wavelengths – and improved the pwer conversion efficiency to 10.6%.
The short-circuit current density, open voltage and fill factor (FF) were 21.7mA/cm2, 0.762 V and 0.641, respectively.