[nanoPost] Organic Photovoltaics: An Alternative to Silicon Solar Cells

Researchers are developing low cost alternative photovoltaics, constructed from a thin film of a cheap composite material, a mixture of carbon nanotubes and conductive polymer.

The goal is power production with zero greenhouse gas
emission by direct photovoltaic conversion of sunlight into
electricity. Silicon solar cells are more commercially mature, but high production costs still limits their commercial viability.

Research Questions
The efficiency of the charge separation process relies on
the conductivity of the polymer (for holes) and carbon
nanotubes (for electrons). The excellent charge-transport
capability of carbon nanotubes is expected to enhance
the conductivity of the mixture.
Preliminary results show poor light conversion efficiency
compared to fullerene-doped systems. Limited polymer
conduction due to disorder in the polymer, and a random
structure of dispersed carbon nanotubes, leading to the
absence of a percolation path are both believed to be
responsible. We are investigating the morphology and
ordering of the nanotube-polymer mixture and their
influence on interfacial traps. A key focus is the
mechanism of polymer wrapping of the nanotubes.

Scanning Tunnelling Microscopy investigations
Scanning Tunnelling Microscopy (STM) has revealed that
the polymer wraps around isolated nanotubes in a regular
fashion. The nanotube can act a template for the
deposition of the polymer, resulting in a highly ordered
form of the polymer, with high conductivity.
The key to highly efficient devices made this way is
achieving a well ordered array of nanotubes, avoiding
clustering.