Rahul Dewan - Jacobs University

Chapter 1
Introduction
1.1 Motivation
Photovoltaic solar cells can play an important role in meeting the ever increasing demand
for energy. With the global energy scarcity that our society faces, the growing
interest in renewable energy sources is quite evident worldwide. In the year 2010 itself
with an installation of 16.6 gigawatts, the photovoltaic market doubled compared
to the previous year when capacity of 7.2 gigawatts was installed [1]. Photovoltaic
technology harnesses, the freely available and emission free, sunlight and converts it
to electricity for our usage.
Thin-film solar cells are promising candidates for future generations of photovoltaic
devices [2]. Whilst current industry standard solar cells use wafer-based silicon (more
than 80 % of the market) [3], an obvious way forward is to reduce the material cost
by using thin-film technology. Thin-film solar cells are usually deposited on low cost
substrates such as glass or plastic [4]. With a much lower fabrication cost for these
thin-film solar cells, the industry for thin-film devices can be promising if their conversion
efficiencies or in turn their price per watt are competitive compared to the price
per watt of wafer based silicon solar cells. The absorber material in thin-film solar cells
are mostly based on: amorphous silicon (a-Si), microcrystalline silicon (µc-Si), copper
indium deselenide (CIS/CIGS) and cadmium telluride (CdTe). In this work the main
focus is on the analysis of thin-film solar cells based on hydrogenated microcrystalline
silicon. Thin-film microcrystalline silicon solar cells have a typical thickness of 0.8–1.5
µm, which is significantly less than the thickness of conventional wafer based silicon
solar cells (180–250 µm) [5].
Reducing the cost and increasing the conversion efficiency is a major objective of
research and development for thin-film silicon solar cells. An approach that simultaneously
achieves these two objectives is to use light-trapping or photon management.
Light trapping facilitates the absorption of sunlight by a thin-film solar cell that is much
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