Theory 80/Energy Limits/Photovoltaics
Solar Cells Have a Band-Gap Limit
The claim
Single-junction solar efficiency is capped by the ratio of band gap to photon energy, producing an optimum gap rather than a monotonic improvement with absorption.
01Mechanism
Gaps too small waste photon excess as heat; gaps too large transmit photons unabsorbed; the product peaks in between.
02Prediction
Efficiency should peak at an intermediate gap.
03Refutation
Efficiency increasing with absorption would remove the trade-off.