### Abstract

The Shockley-Queisser (S-Q) model assumes that the absorptance spectrum of a solar cell is a Heaviside step-function centered at the bandgap energy, i.e. zero below and unity above the bandgap. The absorptance of a practical solar cell is always non-zero below the absorber bandgap. For example, the Urbach tail of bulk semiconductors makes the absorptance an exponential decay function below the bandgap. The presence of an Urbach tail reduces the efficiency when the absorber's bandgap is lower than the optimum value of 1.3 eV predicted by the S-Q model. A very small efficiency improvement (≤ 0.17 %) is possible only for those solar cells with bandgaps greater than 1.3 eV, of which their theoretical efficiency limits are substantially below the S-Q limit. A proof is presented to show that the maximum efficiency is obtained when the absorptance spectrum is a Heaviside step-function centered at the optimum bandgap given by the S-Q model; any other absorptance spectra will not beat this efficiency. A similar approach can be applied to the case of low dimensional structures such as quantum wells, quantum wires/nano wires, and quantum dots.

Original language | English (US) |
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Title of host publication | 2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015 |

Publisher | Institute of Electrical and Electronics Engineers Inc. |

ISBN (Print) | 9781479979448 |

DOIs | |

State | Published - Dec 14 2015 |

Event | 42nd IEEE Photovoltaic Specialist Conference, PVSC 2015 - New Orleans, United States Duration: Jun 14 2015 → Jun 19 2015 |

### Other

Other | 42nd IEEE Photovoltaic Specialist Conference, PVSC 2015 |
---|---|

Country | United States |

City | New Orleans |

Period | 6/14/15 → 6/19/15 |

### Fingerprint

### Keywords

- detailed-balance model
- Shockley-Queisser limit
- Urbach tail

### ASJC Scopus subject areas

- Electrical and Electronic Engineering
- Electronic, Optical and Magnetic Materials

### Cite this

*2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015*[7355801] Institute of Electrical and Electronics Engineers Inc.. https://doi.org/10.1109/PVSC.2015.7355801

**Does below-bandgap absorption improve solar cell efficiency?** / Zhao, Yuan; Liu, Shi; Zhang, Yong-Hang.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

*2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015.*, 7355801, Institute of Electrical and Electronics Engineers Inc., 42nd IEEE Photovoltaic Specialist Conference, PVSC 2015, New Orleans, United States, 6/14/15. https://doi.org/10.1109/PVSC.2015.7355801

}

TY - GEN

T1 - Does below-bandgap absorption improve solar cell efficiency?

AU - Zhao, Yuan

AU - Liu, Shi

AU - Zhang, Yong-Hang

PY - 2015/12/14

Y1 - 2015/12/14

N2 - The Shockley-Queisser (S-Q) model assumes that the absorptance spectrum of a solar cell is a Heaviside step-function centered at the bandgap energy, i.e. zero below and unity above the bandgap. The absorptance of a practical solar cell is always non-zero below the absorber bandgap. For example, the Urbach tail of bulk semiconductors makes the absorptance an exponential decay function below the bandgap. The presence of an Urbach tail reduces the efficiency when the absorber's bandgap is lower than the optimum value of 1.3 eV predicted by the S-Q model. A very small efficiency improvement (≤ 0.17 %) is possible only for those solar cells with bandgaps greater than 1.3 eV, of which their theoretical efficiency limits are substantially below the S-Q limit. A proof is presented to show that the maximum efficiency is obtained when the absorptance spectrum is a Heaviside step-function centered at the optimum bandgap given by the S-Q model; any other absorptance spectra will not beat this efficiency. A similar approach can be applied to the case of low dimensional structures such as quantum wells, quantum wires/nano wires, and quantum dots.

AB - The Shockley-Queisser (S-Q) model assumes that the absorptance spectrum of a solar cell is a Heaviside step-function centered at the bandgap energy, i.e. zero below and unity above the bandgap. The absorptance of a practical solar cell is always non-zero below the absorber bandgap. For example, the Urbach tail of bulk semiconductors makes the absorptance an exponential decay function below the bandgap. The presence of an Urbach tail reduces the efficiency when the absorber's bandgap is lower than the optimum value of 1.3 eV predicted by the S-Q model. A very small efficiency improvement (≤ 0.17 %) is possible only for those solar cells with bandgaps greater than 1.3 eV, of which their theoretical efficiency limits are substantially below the S-Q limit. A proof is presented to show that the maximum efficiency is obtained when the absorptance spectrum is a Heaviside step-function centered at the optimum bandgap given by the S-Q model; any other absorptance spectra will not beat this efficiency. A similar approach can be applied to the case of low dimensional structures such as quantum wells, quantum wires/nano wires, and quantum dots.

KW - detailed-balance model

KW - Shockley-Queisser limit

KW - Urbach tail

UR - http://www.scopus.com/inward/record.url?scp=84961657975&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84961657975&partnerID=8YFLogxK

U2 - 10.1109/PVSC.2015.7355801

DO - 10.1109/PVSC.2015.7355801

M3 - Conference contribution

SN - 9781479979448

BT - 2015 IEEE 42nd Photovoltaic Specialist Conference, PVSC 2015

PB - Institute of Electrical and Electronics Engineers Inc.

ER -