Optical technique could boost solar cell efficiency to 43%

Physicists have developed a new approach to improving solar cell efficiency by controlling light emission. The technique uses an optical resonator to suppress photon emission at wide angles, potentially improving the performance of solar cells.

The Shockley–Queisser limit, which defines the theoretical maximum efficiency of conventional single-junction solar cells, is approximately 33.16%. Researchers at the Institute of Photonic Sciences (ICFO) in Barcelona have identified an optical strategy that could potentially raise this limit to nearly 43%.

The researchers addressed a source of energy loss known as Boltzmann loss. Sunlight enters a solar panel within a narrow cone of angles because the Sun occupies a relatively small area of the sky. However, photons generated inside the solar cell are emitted across a much wider range of angles. This mismatch between the narrow incoming light distribution and the broader outgoing emission reduces the device's effective performance.

To address this problem, the team used an inverted organic solar cell made from a blend of PM6 and Y6 materials. They transformed the cell into an optical resonator by adding a front silver electrode and a second silver electrode at the back.

The resonator suppresses photon emission at wide angles while allowing sunlight to enter. As a result, the angular distribution of emitted light becomes more closely aligned with that of incoming sunlight, potentially reducing energy losses and increasing efficiency.

Lead researcher Francisco Bernal-Texca said the findings represented an important advance in solar energy conversion and opened new possibilities for surpassing the Shockley–Queisser limit.

According to the researcher, the method does not require additional manufacturing complexity, unlike many other approaches to improving solar cell efficiency. Although the experiment was conducted using an organic solar cell, the underlying principle could be applied to a range of photovoltaic technologies.

If successfully incorporated into practical devices, directional control of photon emission could provide another way to generate more electricity from the same amount of sunlight. Higher efficiency could also reduce the land area and materials required for solar power generation, while lowering the cost per watt of electricity produced.