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Thin Film Photovoltaics

Senthilarasu Sundaram*, Katie Shanks*, Hari Upadhyaya**
*ENVIRONMENT AND SUSTAINABILITY INSTITUTE (ESI), UNIVERSITY OF EXETER, PENRYN,
UNITED KINGDOM; **WOLFSON CENTRE FOR MATERIALS PROCESSING, INSTITUTE OF
MATERIALS AND MANUFACTURING, DEPARTMENT OF MECHANICAL, AEROSPACE AND CIVIL
ENGINEERING, BRUNEL UNIVERSITY, LONDON, UXBRIDGE, UNITED KINGDOM
s.sundaram@exeter.ac.uk, hari.upadhyaya@brunel.ac.uk

18.1 Introduction

At present, crystalline silicon (c-Si) dominates more than 90% of the market with module
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efficiencies of 15%–21% and a record lab cell efficiency of 26.6% under 1000 W m [1].
However, the frail nature of the wafers and the bulky nonflexible modules limits the first
generation of silicon technology. Thin film technology has the answers and potential to
eliminate many existing bottlenecks of c-Si photovoltaic (PV) programs experienced at
different levels from module production to its applications in terrestrial, space and build-
ing integration photovoltaics (BIPV). Not only this, but thin film technology lends itself
more easily to improved aesthetics, color, flexibility, and light weight options. Thin film PV
modules can achieve minimum material usage and be manufactured on a large range of
substrates. Some of the advantages of thin film technologies are:
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• The high absorption coefficient (∼10 cm ) of the absorber materials is about 100
times higher than c-Si, thus about 1–2 µm of material thickness is sufficient to harness
more than 90% of the incident solar light. This helps in reducing the material mass
significantly to make modules cost effective.
• The estimated energy payback time of thin film PV is considerably lower than that
of c-Si PV. Estimations suggests that CdTe has the lowest payback time among all PV
technologies. With recent improved cell and modules efficiencies of 17%, the payback
time could be as low as 6 months.
• The formation of heterojunction cells and better device engineering for reduction
of photon absorption losses and enhanced collection of photogenerated carriers are
possible.
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• Large-area deposition (on the order of m ) along with monolithic integration
(interconnection of cells during processing of devices) is possible which minimizes
area losses, handling, and packaging efforts.
• Roll-to-roll manufacturing of flexible solar modules is possible, further reducing the
energy payback time significantly.

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