In 1961 William Shockley and Hans-Joachim Queisser were the first scientist to calculate the maximum theoretical solar cell efficiency using a primitive single p-n junction. The theorectical limit was calculated to be around 33%. That means on a sunny day a silicon solar cell with one p-n junction could collect up to 33% of the sun's rays. Of course the technology was not there to come close to 33%, it was more like 10% for many reasons.
Today researchers are working hard to pass 20% effciency on cost-effective solar cells. Other materials and techniques are being researched to get us past 33% affordably.
Shockley–Queisser limit or detailed balance limit refers to the calculation of the maximum theoretical efficiency of a solar cell made from a single pn junction. It was first calculated by William Shockley and Hans Queisser:
William Shockley and Hans J. Queisser, "Detailed Balance Limit of Efficiency of p-n Junction Solar Cells", Journal of Applied Physics, Volume 32, pp. 510-519 (1961)
The Shockley–Queisser limit is calculated by examining the amount of electrical energy that is extracted per incident photon.
The calculation places maximum solar conversion efficiency around 33.7%assuming a single pn junction with a band gap of 1.4 eV (using an AM 1.5 solar spectrum). Therefore, an ideal solar cell with incident solar radiation will generate 337 Wm-2. When the solar radiation is modelled as 6000 K blackbody radiation the maximum efficiency occurs when the bandgap energy Eg=1.4 eV.