Gas Usage and Cost Management
in Photovoltaics and High-Brightness LEDs
BY DR. ANISH TOLIA
A view of the gases critical to PV and HB-LED
manufacturing, and how they determine the
cost-effectiveness of these devices.
Energy is one of the mega-trends driving the world economy today. Clean energy, particularly photovol- taics (PV), is an area of major investment and growth
as a source of green energy production. Industrial gases
play a very significant role in the manufacturing of photovoltaic cells and a critical part in reducing cost of PV in
the march to grid parity.
Lighting applications account for around one third of
global electricity usage, so energy efficient lighting can
significantly reduce growth in electricity demand. High-brightness LED (HB-LED) lighting is seen as the ultimate
low-power, long-life lighting technology. The HB-LED
industry is also growing rapidly at over 30% per year. Once
again, industrial gases play a significant part in the technology used to manufacture LED chips.
This article aims to highlight the role of gases in these
two important green technologies with emphasis on
efficiency, cost management and scaling for large scale
manufacturing.
Photovoltaics
By the end of 2010, approximately 40G W of solar modules were installed worldwide. 16.6GW of modules were
added—this is solar module installations rather than manufacturing capacity. While the EU demand accounted for
Technology Relative gas intensity
Crystalline silicon cells 1.0 (excluding polysilicon and wafer)
CIGS / Cd Tel thin film
Silicon thin film
0.9 – 1.2
10-20 depending on equipment
supplier
Table 1. Relative gas intensity vs. PV technology
80% of the PV capacity, manufacturing is shifting to Asia.
For instance, China produces around half of the world‘s
crystalline silicon cells and modules.
The market for gases used in PV manufacturing is large,
but varies significantly depending on which technology is
employed to manufacture the PV cells (see Table 1).
Gas requirements for copper indium gallium diselenide
(CIGS) and cadmium telluride (Cd Tel) technologies are
largely bulk atmospheric gases such as nitrogen or argon,
while crystalline or thin film silicon requires a much wider
range of atmospheric and special gases.
Gases in Crystalline Silicon Solar Cell
Manufacturing
While manufacturing processes will vary between
different equipment platforms, the gas component of
a crystalline silicon (c-Si) cell is typically between 2 and
3%. However, with around 60% of the overall cell costs
contributed by the silicon wafer itself, cost management
has largely focused on optimizing wafer production and
reducing silicon losses in the ingot sawing process. Table
2 lists the typical gases used in c-Si processes.
In the primary gas using process, silane and ammonia
are used in combination via plasma deposition to grow
a silicon nitride anti-reflective coating, while carbon tetrafluoromethane is used to plasma etch certain parts of
the wafer.
Currently, many other process steps such as etching
and cleaning are carried out using wet chemicals. However, as cost reduction drives wafers to ever smaller thicknesses (sub - 120µm) some wet processes will become
challenging—not only because of the physical impact on
the wafers, but also due to the very large scale of chemical
