  The Shockley-Queisser (SQ) limit, introduced by W. Shockley and H. J.
Queisser in 1961, is the most well-established fundamental efficiency limit for
single-junction photovoltaic solar cells. For widely-studied semiconductors
such as Si, GaAs and lead-halide perovskite, the SQ limits under standard solar
illumination (1-sun) are 32.7%, 32.5% and 31% for bandgaps of 1.12 eV, 1.43 eV
and 1.55 eV, respectively. Here, we propose that the fundamental efficiency
limits for single-junction solar cells may be surpassed via photon confinement,
substantially raising the theoretical limits to 49%, 45.2% and 42.1% for Si,
GaAs and methylammonium lead iodide (MAPbI3) perovskite cells under 1-sun. Such
enhancement is possible through the containment of luminescent photons within
the solar cell, allowing the suppression of both non-radiative and radiative
recombination losses, which were considered inevitable in the classical SQ
model. Importantly, restricting photon emission from the solar cells raises the
open-circuit voltage (VOC) to values approaching the semiconductor bandgaps,
surpassing the theoretical VOC values predicted by the SQ model. The fill
factors of the cells are expected to increase substantially, resulting in
current-voltage characteristics with very-high squareness for ideal diode
operation. Our work introduces a new framework for improving solar cell
performance beyond the conventional limits.
