Thin film solar cells are a next-generation solution for the renewable energy industry. They possess several benefits over conventional crystalline photovoltaic solar cell technologies, but there are still some limitations to these devices. This article will provide an overview of thin film solar cell technology, materials, applications, benefits, disadvantages, as well as some recent advances in the field.
Image Credit: luchschenF/Shutterstock.com
What are Thin Film Solar Cells?
Thin film solar cells are second-generation devices that are produced by depositing one or more thin layers of photovoltaic materials on a substrate. Common substrates utilized for these photovoltaic devices are plastic, metal, and glass. These devices consist of a photovoltaic material, conductive layer, and a protective sheet.
Layers can vary in thickness, from a few nanometers to several micrometers. This is much thinner than conventional crystalline solar cells, which can be up to 200 µm in thickness. They were originally proposed in 1970, but research officially commenced in 1972. By 1980 researchers were achieving 10% efficiency, and the first commercial panel was released in 1986.
Less semiconductor material is required in the manufacture of thin film solar cells. Strong light-absorbing materials are used in these devices, with the most common being cadmium telluride, copper indium gallium selenide, amorphous silicon, and gallium arsenide. Organic photovoltaic cells have also been explored.
These devices have several key advantages over conventional photovoltaic solar cell technologies. Firstly, they are more lightweight than crystalline silicon cells. Thin film devices can be manufactured with enhanced flexibility, giving them more applications than conventional devices. Additionally, they are potentially cheaper due to the ease of mass production.
This technology possesses some limitations compared to its crystalline counterparts, however. The main issue is with their efficiency, which generally tends to be between 7-18%. The upper limit of crystalline silicon solar cells is 29%, nearly double the efficiency of thin films. Theoretically, however, they could achieve higher efficiency than other technologies, and recent advances have helped to realize parity between these devices and their crystalline counterparts.
Cadmium telluride panels have the lowest carbon footprint of such technologies, but they contain cadmium, a toxic element, requiring special precautions during manufacture, installation, and disposal. Additionally, Telluride is an extremely rare element. Some of these devices are still expensive to manufacture compared to conventional technologies.
Another issue is space. Due to their lower efficiency, more panels are needed to achieve the same power conversion as silicon-based solar cells. This limits their use in domestic dwellings, which still commonly use silicon technologies to meet their power demands. Their low space efficiency requires the use of enhancer technologies, which can be complex and expensive to install.
The shorter lifespan of these devices hinders their widespread commercial application. This requires thin film panels to be replaced more frequently, increasing maintenance costs, and consequently shorter warranty periods are offered to consumers, making them more reluctant to use the technology.
Image Credit: luchschenF/Shutterstock.com
Thin film panels have been explored for their use in several applications. These include commercial and industrial rooftop installations, ground-based solar farms, recreational vehicles, and camping. Being highly flexible, research interest in using these devices for portable and wearable power sources for flexible electronics such as sensors and telecommunication devices has emerged in recent years.
They have also been used in integrated photovoltaics for buildings, such as energy-harvesting windows. Organic photovoltaic thin cell devices have proven especially attractive for this purpose due to the high range of colors and transparency of these panels. This makes them beneficial for both practical and aesthetic elements of building design that can harvest energy directly from the sun without the need for bulky components.
As mentioned, efficiency is a major drawback for thin layer solar cells and panels. However, several studies have reported remarkable advances in efficiency in recent years, bringing these devices closer to full commercialization.
Under standard testing conditions, the efficiency of cadmium telluride panels has reached 19% efficiency, with 22.1% efficiency for single solar cells reported recently. First Solar reported 22.3% efficiency for CIS cells in 2015 CIS. Research has indicated that gallium arsenide cells can reach 39.2% efficiency.
Research has recently focused on increasing the absorption of the technology, such as by incorporating anti-reflective coatings. Additionally, research has been conducted into surface texturing, plasmonic light capture, optimizing solar cell materials, and exploiting nanomaterials such as nanowires and nanoparticles.
The NREL classifies several thin film technologies as emerging photovoltaics. Most of these have not been commercially applied and are still in the R&D phase. These include copper zinc tin sulfide cells, dye-sensitized solar cells, perovskites, quantum dot solar cells, and organic solar cells. Perovskites have been a particular focus, due to their superior properties and efficiencies reaching over 20%.
Concentrator photovoltaics is another recent advance. These third-generation devices combine highly efficient multi-junction solar cells with tracking systems and optical lenses. Whilst many of the technologies still suffer from low efficiency, the potential to produce low-cost, efficient solar energy harvesting technologies has caught the attention of several researchers worldwide. This technology is fast becoming the next revolution in the field of renewable energy.
More from AZoM: How is Potassium Bromide Used in Infrared Spectroscopy?
References and Further Reading
Solar Mag (2022) Thin-Film Solar Panels: An In-Depth Guide | Types, Pros & Cons [online] solarmagazine.com. Available at: https://solarmagazine.com/solar-panels/thin-film-solar-panels/
Planas, O (2019) Thin Film Solar Cell [online] solar-energy.technology. Available at: https://solar-energy.technology/photovoltaics/elements/photovoltaic-panel/photovoltaic-cell/thin-film-solar-cell
NREL (2022) Solar Photovoltaic Technology Basics [online] nrel.gov. Available at: https://www.nrel.gov/research/re-photovoltaics.html