The
impending energy crisis caused by the increasing demand for fossil fuels and
rapidly vanishing fossil fuel reserves, coupled with the threat of climate
change from rising carbon dioxide levels has put renewable energy firmly on the
global agenda. One of the biggest challenges for scientists has become finding
sustainable solutions to address the energy needs of the world, without causing
adverse effects on the environment. Photovoltaic technologies, which can
convert solar energy into electricity without causing harmful emissions, are
one of the most attractive and viable technologies that fulfil this aim. At
present, most of the available photovoltaic products are silicon-based solar
cells. However, the high cost and pollution caused during the manufacture of
silicon-based solar cells have limited their widespread application. Organic
solar cells (OSCs) are one of the most
promising applications for π-conjugated materials due to
their potential to provide a green and cheap solution for the impending energy
crisis.
The device architecture of OSCs are shown in the
Figure a), in which the active layer is sandwiched
between an anode and a cathode. The active layer is typically comprised of a
polymer as a donor and a fullerene derivative (e.g. PCBM) as an acceptor. The
donor and the acceptor materials are intimately blended to form
interpenetrating bicontinuous networks, known as the bulk heterojunction (BHJ)
structure as shown in Figure b). When
light is absorbed by the active layer, coulombically bound electron and hole
pairs, termed excitons, are generated, which diffuse to the donor/acceptor
(D/A) interface where they dissociate. The electrons and holes can subsequently be
efficiently transported to the electrodes.
The focus of this project is
to develop new conjugated polymers, which can serve as the donor material for
organic solar cells. Currently, the polymers we have developed can give power
conversion efficiencies of up to 8%.
Figure 1. a) Device architecture of solar cells. b) Bulk heterojunction structure of active layer of solar cells
Figure 2. Chemical structure of an isoindigo polymer P3TI