This is part of our Advanced Materials are Getting Thinner and Thinner series. In case you missed it, start by reading part 1.
As the photovoltaics industry continues to innovate, considerable progress has been made in eliminating solar panels that use heavy and inflexible silicon substrates. Using thin film technologies, these advances enable easier installation and contoured form factors. An important challenge to alternative energy sources is how energy can be stored once it is collected. And here too thin film technologies play an important role.
Thin film solar panels are typically made with one of the following four material types:
Cadmium Telluride (CdTe) is the most widely used thin film technology. CdTe contains significant amounts of cadmium, which is relatively toxic.
Amorphous Silicon (a-Si), the non-crystalline form of silicon, is a second popular thin film option. With similar technology to that of a standard silicon wafer panel, a-Si is a better option in terms of toxicity and durability, but it is less efficient and is typically used for small load requirements like consumer electronics.
Copper Indium Gallium Selenide (CIGS) cells have reached efficiency highs of 22.4%. Despite considerable interest and research, these performance metrics are not yet possible at scale. In fact, two of the major CIGS manufacturing companies are now bankrupt, including the infamous Solyndra.
Gallium Arsenide (GaAs) is a very expensive technology but holds a world record 28.9% efficiency for all single-junction solar cells. GaAs is primarily used on spacecrafts and is meant for versatile, mass-scale installments for energy collection in unusual environments.
Thin film lithium batteries are an increasingly important field of energy storage, solving the problem of what to do when the sun goes down or the wind stops. Instead of liquid or polymer gel materials, solid-state battery technology uses solid electrodes and a solid electrolyte. Safer and with higher-energy densities, solid-state batteries show promise for pacemakers, wearable batteries, RFID devices and other applications.
In a thin film lithium battery, the electrolyte is solid, and the other components are deposited in layers on a substrate. The solid electrolyte may also serve as a separator material. These materials create flexible batteries cells that are only a few microns thick.
As the demands for safety, higher energy density, and other performance metrics increase, research into anode, cathode, and electrolyte materials has been rapidly progressing. Cathode materials are often complex lithium-oxides such as LiCoO2, LiMn2O4, and LiFePO4, and anode materials are typically comprised of carbon-based materials such as graphite, lithium metal or other metallic materials.
In Part 3, we’ll look at how thin film materials are made.
To learn how thin films can be measured using X-ray diffraction, read our published application note, Investigation of Ni on Si thin film with ARL EQUINOX 100 X-ray Diffractometer.
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