The Voltage Boost Enabled by Luminescence Extraction in Solar Cells

Myles Steiner, Vidya Ganapati, Eli Yablonovitch

Research output: Contribution to conferencePaperpeer-review

1 Scopus Citations


A new physical principle has emerged to produce record voltages and efficiencies in photovoltaic cells, 'luminescence extraction.' This is exemplified by the mantra 'a good solar cell should also be a good LED.' Luminescence extraction is the escape of internal photons out of the front surface of a solar cell. Basic thermodynamics says that the voltage boost should be related to concentration ratio, C, of a resource by ΔV=(kT/q)ln{C}. In light trapping, (i.e. when the solar cell is textured and has a perfect back mirror) the concentration ratio of photons C={4n2}, so one would expect a voltage boost of Δν=Μ ln{4n2} over a solar cell with no texture and zero back reflectivity, where n is the refractive index. Nevertheless, there has been ambiguity over the voltage benefit to be expected from perfect luminescence extraction. Do we gain an open circuit voltage boost of ΔV=(kT/q)ln{n2}, ΔV=(kT/q)ln{2n2}, or ΔV=(kT/q)ln{4n2}? What is responsible for this voltage ambiguity ΔV=(kT/q)ln{4}=36mVolts? We show that different results come about, depending on whether the photovoltaic cell is optically thin or thick to its internal luminescence. In realistic intermediate cases of optical thickness the voltage boost falls in between; ln{n2}qΔV/kT)<ln{4n2}.

Original languageAmerican English
Number of pages3
StatePublished - 18 Nov 2016
Event43rd IEEE Photovoltaic Specialists Conference, PVSC 2016 - Portland, United States
Duration: 5 Jun 201610 Jun 2016


Conference43rd IEEE Photovoltaic Specialists Conference, PVSC 2016
Country/TerritoryUnited States

Bibliographical note

Also published in the IEEE Journal of Photovoltaics: see NREL/JA-5J00-66804

NREL Publication Number

  • NREL/CP-5J00-67936


  • absorption
  • luminescence
  • optical reflection
  • photovoltaic cells
  • radiative recombination
  • substrates


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