= Solution
The \b[<Shockley-Queisser limit>] is the detailed-balance efficiency bound for an ideal single-junction <solar cell> with <radiative recombination> under specified illumination and optical conditions. Below-gap photons are not absorbed and excess energy of above-gap photons is thermalized; radiative emission further limits the output <voltage>. The often quoted unconcentrated terrestrial maximum is roughly one third, not an illumination-independent universal percentage.
A <multi-junction solar cell> places a high-gap junction before lower-gap junctions, dividing the spectrum so photons generate carriers in a better-matched absorber. This reduces transmission and thermalization losses and can exceed the single-junction bound without violating its assumptions: there is now more than one junction. In a two-terminal series stack, all junctions carry the same current, so the lowest photocurrent limits the whole device. \b[Current matching] uses bandgap choice, absorber thickness, optical management and sometimes lateral area to make the generated currents comparable for the intended spectrum. Independently contacted junctions need not share the same current.<Detailed Balance Limit of Efficiency of p-n Junction Solar Cells by William Shockley and Hans J. Queisser>[Single-junction radiative detailed-balance assumptions]{ref}
Back to article page
