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Title: The Voltage Boost Enabled by Luminescence Extraction in Solar Cells

Authors:
; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Light-Material Interactions in Energy Conversion (LMI)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1387712
DOE Contract Number:
SC0001293
Resource Type:
Journal Article
Resource Relation:
Journal Name: IEEE Journal of Photovoltaics; Journal Volume: 6; Journal Issue: 4; Related Information: LMI partners with California Institute of Technology (lead); Harvard University; University of Illinois, Urbana-Champaign; Lawrence Berkeley National Laboratory
Country of Publication:
United States
Language:
English
Subject:
solar (photovoltaic), solid state lighting, phonons, thermal conductivity, electrodes - solar, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly)

Citation Formats

Ganapati, Vidya, Steiner, Myles A., and Yablonovitch, Eli. The Voltage Boost Enabled by Luminescence Extraction in Solar Cells. United States: N. p., 2016. Web. doi:10.1109/JPHOTOV.2016.2547580.
Ganapati, Vidya, Steiner, Myles A., & Yablonovitch, Eli. The Voltage Boost Enabled by Luminescence Extraction in Solar Cells. United States. doi:10.1109/JPHOTOV.2016.2547580.
Ganapati, Vidya, Steiner, Myles A., and Yablonovitch, Eli. 2016. "The Voltage Boost Enabled by Luminescence Extraction in Solar Cells". United States. doi:10.1109/JPHOTOV.2016.2547580.
@article{osti_1387712,
title = {The Voltage Boost Enabled by Luminescence Extraction in Solar Cells},
author = {Ganapati, Vidya and Steiner, Myles A. and Yablonovitch, Eli},
abstractNote = {},
doi = {10.1109/JPHOTOV.2016.2547580},
journal = {IEEE Journal of Photovoltaics},
number = 4,
volume = 6,
place = {United States},
year = 2016,
month = 7
}
  • Over the past few years, the application of the physical principle, i.e., 'luminescence extraction,' has produced record voltages and efficiencies in photovoltaic cells. Luminescence extraction is the use of optical design, such as a back mirror or textured surfaces, to help internal photons escape out of the front surface of a solar cell. The principle of luminescence extraction is exemplified by the mantra 'a good solar cell should also be a good LED.' 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 = {4n 2}; therefore, one would expect a voltage boost of ΔV = (kT/q) ln{4n 2} 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{n 2}, ΔV = (kT/q) ln{2 n 2}, or ΔV = (kT/q) ln{4 n 2}? What is responsible for this voltage ambiguity ΔV = (kT/q) ln{4}more » $${\asymp}$$ 36 mV? Finally, 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{n 2} < (qΔV/kT) < ln{4n 2}.« less
  • Over the past few years, the application of the physical principle, i.e., 'luminescence extraction,' has produced record voltages and efficiencies in photovoltaic cells. Luminescence extraction is the use of optical design, such as a back mirror or textured surfaces, to help internal photons escape out of the front surface of a solar cell. The principle of luminescence extraction is exemplified by the mantra 'a good solar cell should also be a good LED.' 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 = {4n 2}; therefore, one would expect a voltage boost of ΔV = (kT/q) ln{4n 2} 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{n 2}, ΔV = (kT/q) ln{2 n 2}, or ΔV = (kT/q) ln{4 n 2}? What is responsible for this voltage ambiguity ΔV = (kT/q) ln{4}more » $${\asymp}$$ 36 mV? Finally, 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{n 2} < (qΔV/kT) < ln{4n 2}.« less
  • 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 ..delta..V=(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 ..delta..V=kTmore » 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 ..delta..V=(kT/q)ln{n2}, ..delta..V=(kT/q)ln{2n2}, or ..delta..V=(kT/q)ln{4n2}? What is responsible for this voltage ambiguity ..delta..V=(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}q..delta..V/kT)<;ln{4n2}.« less