Limiting efficiencies for multiple energy‐gap quantum devices

We have used a thermodynamic model to calculate theoretical limiting efficiencies for simple and multiple gap solar cells. The limiting efficiency is 26% for a simple solar cell of hydrogenated amorphous silicon, operating at one Sun sensitivity. For a multiple gap cell made from hydrogenated amorphous silicon, together with a second cell, made from a material with lower band gap, it is 38%. The optimum band gap for the second material is 1.0 eV.