Canada: Physicist Sajeev John develops process to boost solar energy generation
An award-winning Indo-Canadian theoretical physicist Sajeev John has developed a process wherein sunlight can be trapped and confined in ultrathin and flexible silicon sheets, offering a far higher efficiency in generating electricity than conventional solar power technology.
Applications based on the research conducted by University of Toronto professor of physics Sajeev John are currently in progress.
In an interview with the Hindustan Times, Prof John, who was born in Thiruvalla in Kerala, said his design is based on “the invention of photonic crystals”, the novel materials that can trap and guide light on a microscopic scale. Certain photonic crystal architectures can be very effective in capturing sunlight and making it bounce around for a prolonged time in a thin material. As a result, the light can be absorbed almost completely in a flexible film of silicon only one-tenth the thickness of a human hair, for highly efficient electrical power generation.
Traditional silicon cells are not ideal at absorbing a broad range of sunlight. While efficient at absorbing shortwave light, they perform poorly with red or near infrared light. In traditional approaches, silicon is made very thick, at 300 microns, thrice the thickness of a human hair, so as to enhance the absorption of sunlight. The problem is that in such thick solar cells, electrons excited by the sunlight need to travel a long distance to metallic contacts and before that, energy dissipates in the form of heat and some of the sunlight doesn’t get converted to electricity.
John’s photonic crystal design is aimed at minimising that wastage with a much thinner structure, only 10 microns thick. “When we can do that and absorb most of the sunlight or more than what they were getting with thick silicon, it means that the photo-generated charge carriers can reach their contacts before they get distracted and de-activated by something else.”
He said the photonic crystal architecture allows for cells that are 50% more efficient than those currently in use. Photonic crystals are also known as the “semiconductors of light” because they control photons much like electronic semiconductors control electrons.
One utility of the invention is that thin silicon solar cells can be encapsulated in flexible sheets to generate power on surfaces like walls, or even in clothing like a winter coat that can provide a charging facility for devices like cellphones.
The invention and development of photonic crystals won John Canada’s highest science and engineering prize, the prestigious Gerhard Herzberg Canada Gold Medal, this month. The award citation said John and his team had “recently applied their light-trapping ideas into the design of flexible, lightweight, thin-film silicon solar cells that can be coated on a variety of surfaces, with unprecedented sunlight capture capabilities and power-conversion efficiencies well beyond that of standard solar panels”.
Research groups in the USA, Germany, Australia, and India are collaborating with John on this potentially breakthrough technology and he is hopeful that real world results leading to applications may emerge in about a year.
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