Polymer-based photovoltaics show promise against silicon and germanium

Yan Jin, a UC doctoral student in the materials science and engineering program, Department of Biomedical, Chemical, and Environmental Engineering, reported results of the research on March 2, at the American Physical Society Meeting in San Antonio, Texas.

Jin described how a blend of conjugated polymers resulted in structural and electronic changes that increased efficiency three-fold, by incorporating graphene into the active layer of the carbon-based materials. The technique is said to have resulted in better charge transport, short-circuit current and a more than 200-per cent improvement in the efficiency of the devices.

‘We investigated the morphological changes underlying this effect by using small-angle neutron scattering [SANS] studies of the deuterated-P3HT/F8BT with and without graphene,’ Jin said in a statement.

The partnership with the Oak Ridge National Laboratory in Tennessee is exploring how to improve the performance of carbon-based synthetic polymers, with the ultimate goal of making them commercially viable.

Unlike the silicon-or germanium-powered solar cells on the market, polymer substances are less expensive and more malleable.

‘It would be the sort of cell that you could roll up like a sheet, put it in your backpack and take it with you,’ said Vikram Kuppa, Jin’s advisor and a UC assistant professor of chemical engineering and materials science.

One of the main challenges involving polymer-semiconductors is that they have significantly lower charge transport coefficients than traditional, inorganic semiconductors, which are used in the current solar technology.

Although polymer cells are thinner and lighter than inorganic devices, these films also capture a smaller portion of the incoming light wavelengths and are much less efficient in converting light energy to electricity.

‘Our approach is significant because we have now shown peak improvement of over 200 per cent on a few different systems, essentially a three-fold increase in the efficiency of the cell by addressing the fundamental problem of poor charge transport,’ said Kuppa.

Jin led the research conducted at Oak Ridge National Laboratory and at UC’s Organic and Hybrid Photovoltaics Laboratory in the UC College of Engineering and Applied Science (CEAS).

‘We’re finding that these enhancements resulted from improvements in both charge mobility and morphology,’ said Jin. ‘The morphology is related to the physical structure of the blend in the polymer films and has a strong impact on the performance and the efficiency of the organic photovoltaic cells.’