Researchers in Spain have developed an optical cavity design for organic solar cells that restricts photon emission angles to suppress Boltzmann losses. The configuration brings emission cones closer to incoming sunlight, pointing toward single-junction efficiencies approaching 43 percent.
Scientists working at the Institute of Photonic Sciences in Spain have tackled a fundamental thermodynamic constraint in photovoltaic conversion by reshaping how solar cells emit light. Their optical configuration targets Boltzmann losses, which stem from a mismatch between the narrow angular range at which sunlight strikes a device and the wide cone over which the photovoltaic material radiates photons back out.
That directional discrepancy increases the entropy of photon emission, which ultimately suppresses the maximum voltage and power conversion efficiency a cell can reach. To counter this, the research team detailed an optical cavity in a study published in Energy & Environmental Science.
Researchers Integrate Inverted PM6 Blends With New Optical Architecture
The investigative team tested their approach using an inverted organic solar cell built upon a PM6 blend. Rather than trying to capture every stray photon through brute-force absorption, the researchers embedded the photovoltaic material inside a specialized optical cavity designed to suppress high-angle emission while maintaining efficient intake of incoming rays.
The physical structure relies on front and rear silver electrodes paired with intermediate layers. The front electrode strongly reflects light attempting to escape at wide angles. Working in tandem with the rear electrode and the surrounding layers, the setup forms an optical cavity that balances broad angular reflectivity with high transmission directly along the path of incident solar radiation.
Engineers Bypass Shockley-Queisser Limits Through Emission Control
Conventional single-junction solar cells face a theoretical efficiency ceiling known as the Shockley-Queisser limit. Under its baseline assumptions, the theoretical limit for a single-junction solar cell is about 33.16 per cent, constrained by intrinsic loss mechanisms like thermal dissipation and the inability of photovoltaic materials to convert low-energy photons into usable electricity.
By narrowing the emission cone to align more closely with the small area the Sun occupies in the sky, researchers estimate that efficiencies could, in principle, approach 43 per cent. This strategy moves optimization away from solely chasing absorption gains and toward managing radiative losses.
Teams Propose Future Technology Scaling and Manufacturing Simplicity
Collaborating with researchers from the Polytechnic University of Catalonia, the team noted that integrating the optical cavity does not require complex fabrication steps compared to other efficiency-boosting methods under exploration. Although demonstrated on an organic photovoltaic device, the underlying principle is not restricted to organic blends and could potentially be extended to other solar cell technologies.
Controlling photon emission to generate more electricity per unit area could eventually reduce the physical land and material footprint required for large-scale solar installations.