Back-Surface Recombination, Electron Reflectors, and Paths to 28% Efficiency for Thin-Film Photovoltaics: A CdTe Case Study

Joel Duenow, Wyatt Metzger

Research output: Contribution to journalArticlepeer-review

45 Scopus Citations

Abstract

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.

Original languageAmerican English
Article number053101
Number of pages6
JournalJournal of Applied Physics
Volume125
Issue number5
DOIs
StatePublished - 7 Feb 2019

Bibliographical note

Publisher Copyright:
© 2019 Author(s).

NREL Publication Number

  • NREL/JA-5K00-73045

Keywords

  • back surface recombination
  • CdTe
  • electron reflector
  • lifetime

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