Back-surface recombination, electron reflectors, and paths to 28% efficiency for thin-film photovoltaics: A CdTe case study

As thin-film and silicon solar technologies mature, questions emerge about the upper bounds of thin-film solar performance and realistic experimental paths to reach them. Directions include increasing absorber hole density and bulk lifetime, improving the junction interface, reducing back-surface re...

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Bibliographic Details
Published in:Journal of applied physics 2019-02, Vol.125 (5)
Main Authors: Duenow, Joel N., Metzger, Wyatt K.
Format: Article
Language:English
Subjects:
Absorbers
Applied physics
back surface recombination
Bulk density
Cadmium tellurides
Carrier lifetime
CdTe
Efficiency
electron reflector
Electrons
Hole density
Identification methods
lifetime
MATERIALS SCIENCE
P-n junctions
Passivity
Photovoltaic cells
Reflectors
Solar cells
SOLAR ENERGY
Thin films
Upper bounds
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Summary:As thin-film and silicon solar technologies mature, questions emerge about the upper bounds of thin-film solar performance and realistic experimental paths to reach them. Directions include increasing absorber hole density and bulk lifetime, improving the junction interface, reducing back-surface recombination, and implementing a back-surface electron reflector. Textbook solutions of idealized p-n junctions create a powerful conceptualization of solar cells as predominantly minority-carrier-driven devices. We demonstrate that thin films are distinct, and models often fail to capture the important role of majority-carrier lifetime, leading to contradictions with lifetime measurements and overestimates of potential device improvement from back-surface passivation and/or reflectors. Furthermore, we identify methods to probe majority-carrier lifetime and re-examine the degree to which back-surface passivation and electron reflectors can increase efficiency for a range of common thin-film interface and absorber properties, using current and emerging CdTe technology as an example. Results indicate that a practical approach is to focus first on improving front-interface recombination velocity and the absorber properties, and then on implementing the back-surface passivation or reflector, which can ultimately allow thin-film solar technology to reach 28% efficiency.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.5063799