Effect of thermal radiation entropy on the outdoor efficiency limit of single-junction silicon solar cells

Abstract

Incoming radiation energy illuminating a solar cell contains a certain amount of entropy, which does not contribute to output electrical work. Entropy has a different spectral distribution from the internal energy of light and consequently affects PV cell performance. Here in this work, we investigate the influence of entropy content of thermally radiated light on the maximum achievable efficiency of single-junction solar cells. We revise the value of the well-known Shockley-Queisser (SQ) limit for various absorber materials and take a deeper look at this effect by re-calculating the efficiency limit of crystalline silicon solar cells considering Meitner-Auger recombination. When considering the entropy content of AM 1.5 standard spectrum, the SQ limit for silicon drops from 33.15% to 30.42%. Further, considering Meitner-Auger recombination and using measured properties of silicon, the efficiency limit lowers to 27.12% from the already established 29.43%. This suggests a 4% thinner silicon absorber, reaching a thickness of ∼101 μm; hinting PV industry that a thinner Si wafer can provide the optimum outdoor energy yield. We further show that the entropy content of terrestrial radiation is less in favor of c-Si technology and most in favor of amorphous silicon. In the end, we discuss a few applications of considering entropy of incoming sunlight for photovoltaics, which range from PV device design to PV module tilt optimization and even PV system electrical standards. • Quality of radiation that a solar cell receives changes under outdoor condition. • Radiation illuminating solar cells in labs has lower entropy, i.e. higher exergy. • Exergy of incoming radiation is used to calculate outdoor efficiency limit. • Single junction solar cells can reach 27.1% efficiency under outdoor condition. • Results suggest 4% thinner silicon absorbers for single junction solar cells.