Reaching beyond efficiency limits


So-called “hot carrier” solar cells (HCSCs) offer one theoretical path to conversion efficiencies beyond today’s theoretical limits. By isolating and capturing energy from particles carrying excess kinetic energy that is usually lost as heat, the concept promises cell efficiencies well beyond 30%, even for a single junction device.

The theory has been around for several decades, but so far, no hot carrier cell has been successfully fabricated. The “imperfections” that would limit practical performance of such a device, in comparison to models of what is theoretically possible, are not well understood.

Scientists led by Japan’s University of Tokyo investigated the resilience of HCSCs to these “non-ideal” scenarios, and introduced a “hot carrier multijunction solar cell” (HCMJ) as an approach that modeling showed could be less vulnerable. They described the research in “Hot carrier multijunction solar cells: sensitivity and resilience to nonidealities,” which was recently published in Journal of Photonics for Energy.

While the model showed the HCSC as having the highest efficiency potential, the HCMJ demonstrated a lower drop in performance when other non-optimal designs were used. They also model performance of the cells under different light and temperature conditions, and were able to widen the list of materials potentially suitable for hot carrier devices.

“Hot-carrier photovoltaics have been proposed since the early 1980s as a way to achieve higher efficiencies that break the conventional ‘detailed-balance’ limit, but they have yet to be realized in practice,” explained Sean Sheehan, editor-in-chief of the journal that published the research. “The work by Giteau and colleagues provides a strategy to bring them closer to fruition by loosening the constraint of near-perfect materials, which otherwise easily reduces the performance of real-world devices.”

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