Progress in Photovoltaics Research and Applications · 2010 · 591 citations · 15 references
EngineeringElectrical EngineeringMaterials SciencePhotonicsSemiconductor DevicesSemiconductor MaterialsPhotovoltaic DevicesSolar CellsSolar Photovoltaic SystemsSolar RadiationThermal Properties Of SemiconductorsWide Band Gap SemiconductorsCarnot EfficiencyCarrier ConfinementCell EfficiencyDevice EfficiencyDiscrete Energy LevelsPhoton EmissionRecombination LossesSolar Cell Device Physics
This paper considers intrinsic loss processes that lead to fundamental limits in solar cell efficiency. The authors quantify five intrinsic loss processes that account for all incident solar radiation. An analytical approach is used to evaluate all five losses, providing a complete mathematical and graphical description of the mechanisms and showing that dominant losses in concentrator and spectrum‑splitting cells can be avoided with novel designs. The study finds that free energy per carrier is limited by Carnot and Boltzmann factors, that degenerate band absorbers gain a free energy advantage through entropy transfer during cooling, and that non‑absorption of sub‑bandgap photons and photon emission are current‑limiting processes, with all losses mathematically described and indicating that dominant.
Abstract This paper considers intrinsic loss processes that lead to fundamental limits in solar cell efficiency. Five intrinsic loss processes are quantified, accounting for all incident solar radiation. An analytical approach is taken to highlight physical mechanisms, obscured in previous numerical studies. It is found that the free energy available per carrier is limited by a Carnot factor resulting from the conversion of thermal energy into entropy free work, a Boltzmann factor arising from the mismatch between absorption and emission angles and also carrier thermalisation. It is shown that in a degenerate band absorber, a free energy advantage is achieved over a discrete energy level absorber due to entropy transfer during carrier cooling. The non‐absorption of photons with energy below the bandgap and photon emission from the device are shown to be current limiting processes. All losses are evaluated using the same approach providing a complete mathematical and graphical description of intrinsic mechanisms leading to limiting efficiency. Intrinsic losses in concentrator cells and spectrum splitting devices are considered and it is shown that dominant intrinsic losses are theoretically avoidable with novel device designs. Copyright © 2010 John Wiley & Sons, Ltd.
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