Using an inexpensive method to make the surface of solar cells rougher, scientists in Japan have created efficient solar panels that do not require antireflective coatings.
AsianScientist (Aug. 7, 2017) – A team of researchers at Osaka University in Japan have modified the surface texture of both the front and back of silicon solar cells to inexpensively enhance their light harvesting and power conversion efficiency. They published their findings in Solar RRL. The efficiency of power generation using solar panels depends on getting as much electricity as possible out of the panels while keeping the manufacturing costs low. Engineers and researchers are finding new ways to obtain power out of solar modules, but doing so without adding to their costs is becoming more and more difficult. Antireflective coatings, like those used on reading glasses, can help to get more light into solar cells and boost their electricity output. However, these coatings are expensive to produce, especially when they are required to cover large areas. In this study, a team of scientists at Osaka University created low reflection silicon cells by fabricating so-called black silicon using an inexpensive method known as surface structure chemical transfer (SSCT). “Unmodified silicon solar cells lose light energy in the form of reflection, so most solar cells have some kind of antireflective coating,” explained Dr. Daichi Irishika of Osaka University. “To avoid using these extra coatings, we fabricated a submicron structure using a simple wet treatment directly into the silicon surfaces to give the cell its own antireflective coating.” Essentially, SSCT involves the chemical treatment of the front side of silicon cells to produce tiny submicron silicon structures which prevent light reflection and give a black appearance. The team also developed a method to passivate the submicron silicon structures with huge surface area to prevent the recombination loss during the deposition of phosphosilicate glass followed by heat treatment. This method can simultaneously form a PN junction—a boundary or interface between two types of semiconductor material—to separate photo-generated electrons and holes. Hence, their technique does not add to the complexity of the manufacturing process. The Osaka team then turned their attention to the reverse side of the silicon cells and created rougher light-trapping microstructures to capture even more infrared light. Their results have taken them a step closer to making inexpensive solar cells that can deliver the same high efficiency as more complex and expensive cells. “Making very high efficiency solar cells is important but we should also consider the economics and practicality of any processes used to increase efficiency,” said Professor Hikaru Kobayashi of Osaka University. “The wet processes we have developed are simple yet effective, and our work with black silicon has real-world applications in making cost-effective silicon solar panels.”