Indium Tin Oxide-Free Polymer Solar Cells: Toward Commercial Reality - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 187

Fig. 2 Energy payback time for PV modules technologies. South Mediterranean irradiance
(1,700 kWh/m 2 /year) and a performance ratio of 0.8 are assumed. The module efficiency is shown
in brackets. DS stands for dye sensitized modules and A and B refer to the low and high values of
the energy range. Process One is ITO-based PSCs, Process H is ITO-free PSCs, SFE is metal- and
ITO-free PSCs
more economically competitive. Since most mature solar cells already operate at
or near theoretically permissible efficiencies, the need for cost reduction in
materials and processing has driven the development of solar cell technology from
the first to the third generation.
The first generation of monocrystalline silicon is grown in the form of ingots
via the Czochralski process that requires Si to be in molten form which is achieved
at [1400 C. The EPBT of [2 years for such cells despite its high efficiency and
lifetime clearly indicates the relatively exorbitant energy investment that the first
generation PV requires in comparison to other technologies (Fig. 2 ). The need to
compensate such a slow and high energy input processing led to the development
of second generation solar cells. The latter could be produced faster using tech-
niques such as sputtering and chemical vapor deposition routes and employing
cheaper materials albeit at a cost to performance.
The third generation of organic solar cells is pursued, despite the relatively
lower expected efficiency and lifetime in comparison to the former generations,
primarily because of their potential at drastic reduction in materials and production
cost. Such a potential is envisioned accomplishable through high throughput roll-
to-roll production with coating and printing at low temperatures that common
plastic substrates such as PET can withstand (\140 C). The initial experiments on
large-area indium tin oxide (ITO)-based PSC modules produced by complete roll-
to-roll production [ 3 , 4 ] and their subsequent cost analyses [ 1 ] revealed that the use
of ITO is not feasible in the low-cost production of PSCs. ITO is a commonly used