Driven to increase the power output from solar cells – one of the most important sources of renewable energy globally – the Hosein Research Group at Syracuse University has developed a new type of polymer coating that enables a solar cell to convert more light into electricity. The coating consists of 1000s of microscale fiber optic elements that transform the coating into a powerful collector of light, ensuring as much solar energy that shines on the solar cell can be captured and converted. Furthermore, the coating widens the angular range of collection, enabling the significant capability to collect more light over the course of the day and across seasons.
Solar cells are typically coated with a thin transparent polymer film, often referred to as an encapsulant, that protects the sensitive semiconductor material from possible physical or chemical damage (e.g., handling, extreme weather conditions). The coating is generally uniform, consisting of no internal structure. Consequently, such an encapsulated solar cell suffers from significant losses owing to the dispersive nature of light, shading from the electrical top-contacts, as well as reflection. There have been several efforts to incorporate different types of optical elements within an encapsulant to direct more light towards the active regions of the solar cell. Examples include particle coatings, diffraction and diffuse layers, geometric optical structures, and cloaking of the top-contacts.
The coatings developed by the Hosein Research Group realized a radically different approach. Transparent polymer films were fabricated that consist of a vast array of microscale cylindrical optical fibers. As in the case of conventional fiber optics, these microscale elements possess the capability to collect light, confine it within its structure, and direct it along its length across the thickness of the film. The result: more light being received by the solar cell and the mitigation of any potential losses.
One novelty of the work is in the way the coatings were made. The array of fibers was produced by irradiating a two-component photocurable mixture with blue LED light. An optical mask pattern was employed to divide the light source into a large-scale array of microscale optical beams that are transmitted through the mixture. Through a spontaneous, light-driven phase separation process, each beam induces the formation of a fiber along its length consisting of a high refractive index core (from one component) and low index surroundings (from the other). This establishes the refractive index profiles for optical waveguiding light.
Prototype encapsulated solar cells showed a significant increase in the conversion efficiency. Furthermore, measurements of conversion at different incident angles of light showed that more light was converted as compared to a conventional uniform coating, thereby demonstrating enhanced wide-angle capture. Overall, the coatings show approximate 10% enhancement in optical energy conversion that, on the current GW scale of energy production of most solar cell farms, would translate to a significant boost in energy generation.
The significant advantages of this approach are the simplicity and scalability in which the materials can be produced, whereby large-scale solar modules may be coated, as well as the potentially significant increase into the total solar energy converted into electricity.
These findings are described in the article entitled Polymer Encapsulants Incorporating Light-Guiding Architectures to Increase Optical Energy Conversion in Solar Cells, published in the journal Advanced Materials. This work was led by Ian D. Hosein from Syracuse University.