NREL CIGS devices with up to 20% efficiency are prepared using a three-stage process for the CIGS layer with the last
step of an intrinsic ZnO and conductive ZnO:Al bilayer. This work outlines the efficiency and performance parameters
for these CIGs devices when this bilayer is replaced with indium zinc oxide (a-InZnO), an amorphous metal oxide. It is
well known that metal oxides can serve a variety of important functions in thin film photovoltaics such as transparent
electrical contacts (TCO's), antireflection coatings and chemical barriers. In the case of a-InZnO, we have reported on
the determination of the relative roles of metals and oxygen stoichiometries on the opto-electronic properties of a-InZnO
thin films as well as the stability of those films in damp heat. Since InZO has a tunable conductivity based on the
amount of oxygen introduced during deposition, it can be used as both the intrinsic and TCO layers. We were able to
establish preliminary metrics for an all InZnO bilayer whose performance was comparable to a common CIGs device.
Relatively high proven efficiencies of CIGS devices are often cited regarding its choice as a semiconductor for
photovoltaic manufacturing. Module efficiency is an important parameter, as a number of factors in the cost per watt are
driven downward by increasing efficiency. Some of these factors include materials costs, throughput for a given capital
investment, and installation costs. Thus, realizing high-efficiency (e.g. 15%) large-area CIGS modules is key in both
reducing cost per watt and differentiating the technology from other thin films. This paper discusses the material
properties required of each layer of the CIGS device such that large-area CIGS modules can achieve efficiencies 15%,
which is substantially higher than the current industrial state-of-the-art. The sensitivity of module performance to the
important material parameters is quantified based on both experimental data and modeling. Necessary performance
differences between small-area devices and large-area modules imposed by geometry are also quantified. Potential
technical breakthroughs that may relax the requirements for each layer are discussed.
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