Cadmium Telluride in Photovoltaic Devices
by Mitchell Sharum
Photovoltaics currently account for 3.6% of global energy production, but as technologies improve at a staggering rate, the different paths for solar energy stand to be considered. As top companies rush towards the production of quickly cheapening solar energy, they are faced with a number of tradeoffs associated with the materials that they use. Solar cells (semiconductor devices that convert sunlight to electricity) are commonly developed from two different materials, the first (and most common) being crystalline silicon. Crystalline silicon cells have a lifespan of approximately twenty five years. These cells can be divided into three types: monocrystalline, polycrystalline, and amorphous cells, which are ordered from most expensive to cheapest. Moving down the line, these types of silicon cells also grow less absorbent of energy, with monocrystalline silicon panels claiming the title of most efficient PV material. Amorphous cells have a maximum efficiency of 13% (i.e. 13% of the energy that comes into the panel from the sun gets converted to usable energy), and are considered to be “thin-film” photovoltaic devices. Another common semiconductor material used for the production of solar energy is Cadmium Telluride (CdTe). Solar cells constructed with CdTe also have thin photovoltaic films, and are primarily employed in the industrial processes of smaller solar companies. Some larger institutions like First Solar, though, exclusively produce photovoltaic devices with Cadmium Telluride, looking hopefully towards its future.
Even among thin-film solar cells there are choices to be made. Each different set of elemental materials carry with them a unique set of costs and benefits, which manufacturers must consider in pursuit of sustainability both as it applies to their company and to the larger environment. Cadmium Telluride, for instance, does have a lower efficiency than most silicon based PV films, but it also is able to capture sunlight at shorter wavelengths. That is to say that, even though it absorbs less light right now, CdTe has the capacity upon further research to pull energy from a greater bandwidth than its counterparts. At the same time, photovoltaic devices that implement CdTe are less costly to produce than their silicon counterparts. Many top competitors in the solar market opt for silicon instead, citing a few of the benefits of crystalline silicon-based panels. Such panels top out at 24% efficiency, which is more than double the efficiency of the average CdTe panel. Such a large difference in energy production could justify a more costly production process. Moreover, silicon is the second most abundant element in the earth's crust, and though Cadmium is extremely easy to find, Tellurium is considered one of the earth's rarer materials, accounting for only 1 to 5 parts per million in the earth’s crust.
Ultimately, the choice can not be made less subjective without further research and development performed on CdTe, which has received far less attention since its inception than the industry staple of monocrystalline silicon. The former has been tested and verified in hot, humid climates, and have held up structurally through degrading conditions. For now, optimists and innovators alike hold out hope for the potential of this fascinating solar technology.
References: Solar Energy Production, Solar Cell Materials, Solar Tech Deep Dive