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Organic Photovoltaics

Ross A. Hatton
WARWICK UNIVERSITY, COVENTRY, UNITED KINGDOM
Ross.Hatton@warwick.ac.uk

12.1 Introduction

As part of a global effort to curb CO 2 emissions the past decade has seen a dramatic ac-
celeration in the deployment of crystalline silicon PVs, spurred by unprecedented reduc-
tions in manufacturing costs and state subsidies [1,2]. In many parts of the world the cost
of electricity produced by large-scale silicon PV installations is now competitive with that
produced using conventional fossil fuels, which is transforming the global energy generat-
ing sector [1,2]. However, for expansion of the range of PV applications for integration into
buildings, transportation, and consumer electronics there is a need for PV technologies
that are compatible with light weight and flexible substrates and whose color can be engi-
neered to match the intended application, the latter of which is particularly important for
consumer acceptance.
In conventional inorganic semiconductors such as silicon, the atoms are held together
by strong covalent bonds and the thickness of semiconductor needed for PV applications is
of the order of 100 µm [3,4]. For crystalline and multi-crystalline silicon PVs, which are the
dominant PV technologies of today [1], the optimal semiconductor thickness is ∼150 µm,
which is comparable to the thickness of a piece of A4 paper. For silicon this large thickness
is needed due to its relatively weak absorption of near-infra red light, which makes up a
large proportion of the useful solar spectrum for PV applications [4]. Consequently, PVs
based on conventional semiconductors are inherently brittle and must be supported on
rigid flat plate substrates (e.g., glass), which renders them heavy and unsuitable for use in
many important emerging application areas. For example, the electrification of transport
systems across the world is progressing rapidly [5], and the roofs of cars and lorries are
ideal platforms for PV modules provided the energy required to transport the extra weight
is small compared to the electrical energy generated. For automotive applications the PV
module must also be very low profile and conformal to the contours of the vehicle, so as
not to increase fuel consumption due to increased air flow drag, but also for consumer
acceptance. These requirements make silicon PVs wholly unsuitable for this application
space. Similarly for portable consumer electronics, for which there is a strong case for inte-
gration of PVs as a source of auxiliary power to reduce the time between battery recharges
and to enable the relentless demand for increased functionality and computing power.

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