Projected increases in global energy demand, predicted to be as
high as 1 GW/day, will place significant strains on current energy
infrastructure [1]. This looming challenge, coupled with depleting
traditional fossil-fuel based energy sources and the threat of climate
change, requires the development of renewable energy
technologies. Of the possible renewable energy approaches, photovoltaics
(PV), the conversion of sunlight into electricity, represents
a promising route. The current photovoltaics landscape is
dominated by silicon solar cells, which have benefited from recent
advances leading to reduced manufacturing costs [2]. However,
this mature technology is constrained by some fundamental cost
barriers, such as high temperature processing. A fundamental shift
in thinking may allow for significantly reduced processing costs.
One such alternative approach involves replacing the crystalline
silicon with organic semiconductors. The key advantage of this
approach is the possibility of manufacturing solar modules using
solution processing techniques, which significantly reduces the
cost and energy payback time [3–5]. In fact, Espinosa et al. proposed
that a polymer solar cell module could be fabricated with an
energy payback time of only one day, given advances in efficiency
and stability [1]. Over a period of approximately 20 years, the
power conversion efficiency (PCE) of polymer solar cells progressed
to 12% [6]. Importantly, several demonstrations have
shown that polymer solar cell modules may be fabricated using
solution based printing and coating techniques and installed with
an installation rate of 4200 Wp/min [7,8]. Whilst multiple small
area devices, fabricated in ideal laboratory settings, have achieved
PCEs above 10% [9–12], the demonstrations of large scale polymer
solar modules suffer from low efficiency. The system efficiency for
the solar park demonstration was o2% [7]. Whilst these represent
initial reports, much improvement is required in this area.