Emitter/absorber interface of CdTe solar cells
Abstract
The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a “spike,” creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a “cliff” (ΔEC < 0 eV) allows high hole concentration in the vicinity of the interface, whichmore »
- Authors:
-
- Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA
- National Renewable Energy Laboratory, Golden, Colorado 80401, USA
- Publication Date:
- Research Org.:
- National Renewable Energy Laboratory (NREL), Golden, CO (United States)
- Sponsoring Org.:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office; U.S. Department of Energy SunShot program
- OSTI Identifier:
- 1257658
- Alternate Identifier(s):
- OSTI ID: 1257863; OSTI ID: 1270791
- Report Number(s):
- NREL/JA-5K00-66287
Journal ID: ISSN 0021-8979; JAPIAU; 10.1063/1.4953820
- Grant/Contract Number:
- AC36-08GO28308; UGA-0-41027-18
- Resource Type:
- Published Article
- Journal Name:
- Journal of Applied Physics
- Additional Journal Information:
- Journal Name: Journal of Applied Physics Journal Volume: 119 Journal Issue: 23; Journal ID: ISSN 0021-8979
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 14 SOLAR ENERGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CdTe; numerical modeling; interface recombination; semiconductors; electronic transport; electronic bandstructure; computer simulation; photoconductivity; charge recombination; interface defects; heterostructures; electrical properties and parameters; solar cells
Citation Formats
Song, Tao, Kanevce, Ana, and Sites, James R. Emitter/absorber interface of CdTe solar cells. United States: N. p., 2016.
Web. doi:10.1063/1.4953820.
Song, Tao, Kanevce, Ana, & Sites, James R. Emitter/absorber interface of CdTe solar cells. United States. https://doi.org/10.1063/1.4953820
Song, Tao, Kanevce, Ana, and Sites, James R. Fri .
"Emitter/absorber interface of CdTe solar cells". United States. https://doi.org/10.1063/1.4953820.
@article{osti_1257658,
title = {Emitter/absorber interface of CdTe solar cells},
author = {Song, Tao and Kanevce, Ana and Sites, James R.},
abstractNote = {The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a “spike,” creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a “cliff” (ΔEC < 0 eV) allows high hole concentration in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. Another way to mitigate performance losses due to interface defects is to use a thin and highly doped emitter, which can invert the absorber and form a large hole barrier at the interface. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. The ΔEC of other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ΔEC. As a result, these materials are predicted to yield higher voltages and would therefore be better candidates for the CdTe-cell emitter.},
doi = {10.1063/1.4953820},
journal = {Journal of Applied Physics},
number = 23,
volume = 119,
place = {United States},
year = {Fri Jun 17 00:00:00 EDT 2016},
month = {Fri Jun 17 00:00:00 EDT 2016}
}
https://doi.org/10.1063/1.4953820
Web of Science
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