What is the efficiency limit of a single-junction silicon solar cell?

Silicon solar cells have an indirect bandgap, and so radiative recombination is an inefficient process. As such, their maximum power conversion efficiency is assumed to be less than the Shockley–Queisser limit, which has historically been associated with the radiative recombination process that results in luminescence radiation. Instead, the Auger–Meitner recombination process that ultimately results in thermal radiation is thought to prevent silicon solar cells from reaching the Shockley–Queisser limit. However, the Shockley–Queisser formalism is fundamentally based on a balance between the absorbed radiation and externally emitted recombination radiation, regardless if this is luminescence radiation or thermal radiation. Therefore, the limiting efficiency of a 1.12 eV bandgap silicon solar cell is 33.4% when the cell is irradiated by the standard AM1.5G solar spectrum and the temperature of the cell is 298.15 K. This revised efficiency limit is larger than the reported efficiency limit of 29.4% for the same solar spectrum and cell temperature. In general, while Auger–Meitner recombination is a loss in light-emitting diodes, it is not necessarily a loss in solar cells. In order to achieve peak power conversion efficiency, luminescence radiation and thermal radiation should be emitted externally out of the cell. Additionally, thinning the cells without sacrificing current density will result in reduced entropy per photogenerated electron, and this will help in the quest to maximize the voltage.