Today’s silicon-based photovoltaics have a number of limitations: they’re heavy, rigid, and, without subsidies, not cheap. Researchers are exploring new solar technologies that can provide clean, renewable energy without these limitations. These emerging technologies include dye-sensitized solar cells, organic photovoltaics, perovskite photovoltaics and inorganic quantum dot solar. These four new types are expected to be less expensive, thinner, have greater flexibility and be adjustable to a variety of light conditions, which can increase the range of solar beyond conventional rooftop and solar farm applications. Medical Advocates for Healthy Air believes that these new solar technologies could help mitigate climate change by moving North Carolina toward a clean, emission-free energy mix and may even change the dynamics of solar demographics by making the technology more affordable and less reliant on access to a grid. Here is a rundown of how these technologies work.
Conventional silicon photovoltaics
Silicon photovoltaics require ultra-high purity silicon, and their manufacture involves a very energy-intensive process of vapor deposition and crystal growth. Because silicon is inefficient at absorbing sunlight, silicon photovoltaics require thicker cells. The heavy glass that is needed to support thicker cells adds to cost and restricts applications. For example, rooftops must be sturdy enough to support the weight of the glass panels. The maximum efficiency for today’s top performing silicon cells is 21% and the record efficiency of 25% belongs to a scarce and expensive single-crystal silicon cell. These efficiencies may make silicon cells seem better compared to the emerging solar cells but the emerging solar cells promise to be thinner and more flexible for an increased range of applications, not to mention less expensive. This means, soon, solar technology will no longer be limited to rooftops and solar-farm panels.
Dye-sensitized and perovskite cells are expected to use 1000 times less light-absorbing material than silicon cells and are made from inexpensive materials with the same inexpensive techniques used in plastic manufacturing.
Dye-sensitized solar cells (DSSCs)
Dye-sensitized solar cells, coated with a dye that captures any kind of light and converts it to electricity by transporting electrons through molecular layers, have a maximum efficiency of about 11.9%. Although DSSCs are less efficient than silicon cells, they still have valuable features such as light weight, thinness, flexibility and low cost, that open it up to niches like building-integrated photovoltaics, in which solar panels cover any exterior surface of a building, including windows and skylights. DSSCs can also be applied on smaller scales such as on vehicles or even on electronics. This is based on what is known as “the internet of things” which represents a network of devices and vehicles with sensors and other electronic devices design to collect and transmit information. The primary advantage, however, is the ability of DSSCs to generate electricity from indoor light sources. This is where DSSCs really beat silicon cells. This feature allows them to easily generate power to support indoor electronics.
These cells have an efficiency of about 11.5%. Organic photovoltaics use a mixture of organic, earth-abundant compounds to absorb light and manipulate electrons. They can be produced via large-scale roll-to-roll printing. Like the DSSCs, these cells are also thin, light-weight and flexible, useful for building exteriors and for irregularly-shaped objects like backpacks. Current research focuses on increasing device efficiency and lifetime.
Perovskite solar cells
Although a lot of other solar cells are still not as efficient as conventional silicon, perovskite solar cells may just become the efficiency enthusiast’s favorite. At a maximum efficiency of 22.1%, perovskite cells use compounds that are very good at absorbing light. Engineers are also exploring the potential for a perovskite-silicon hybrid which can be used for rooftop applications. This hybrid absorbs more of the solar spectrum than silicon, making it more powerful than conventional silicon panels. Unfortunately, stability is an issue as the light-sensitive component of perovskite is prone to deterioration when exposed to water and high temperatures. Research is underway to reduce the chance of lead contamination, which must be solved before large-scale commercialization can be considered.
Quantum dot photovoltaics
Quantum dot solar cells have metallic compounds that allow them to work as good light absorbing material within the cells. They have a maximum efficiency of 11.3% and can be produced by low-cost chemistry methods and high-speed printing techniques. This technology requires specialized machinery and technical expertise, which is hindering business investment. One company, Solterra, expects to demonstrate a multicell module within two years.
Credit: Jacoby, Mitch. “Commercializing Low Cost Solar Cells.” Chemical and Engineering New 2 May 2016: 30-34.