Luminescence Methodology to Determine Grain-Boundary, Grain-Interior, and Surface Recombination in Thin-Film Solar Cells

John Moseley, Eric Colegrove, Harvey Guthrey, Darius Kuciauskas, Helio Moutinho, Mowafak Al-Jassim, Wyatt Metzger, Pierre Rale, Stephane Collin

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27 Scopus Citations


We determine the grain-boundary (GB) recombination velocity, S G B, and grain-interior (GI) lifetime, τ G I, parameters in superstrate CdS/CdTe thin-film solar cell technology by combining cathodoluminescence (CL) spectrum imaging and time-resolved photoluminescence (TRPL) measurements. We consider critical device formation stages, including after CdTe deposition, CdCl2 treatment, and Cu diffusion. CL image analysis methods extract GB and GI intensities and grain size for hundreds of grains per sample. Concurrently, a three-dimensional CL model is developed to simulate the GI intensity as a function of τ G I, S G B, grain size, and the surface recombination velocity, S surf. TRPL measurements provide an estimate of S surf for the CL model. A fit of GI intensity vs. grain size data with the CL model gives a self-consistent and representative set of S G B and τ G I values for the samples: S G B (τ G I) = 2.6 × 106 cm/s (68-250 ps), S G B (τ G I) = 4.1 × 105 cm/s (1.5-3.3 ns), and S G B (τ G I) = 5.5 × 105 cm/s (1.0-3.8 ns) for as-deposited, CdCl2-treated, and CdCl2- A nd Cu-treated samples, respectively. Thus, we find that the CdCl2 treatment both helps to passivate GBs and significantly increase the GI lifetime. Subsequent Cu diffusion increases GB recombination slightly and has nuanced effects on the GI lifetime. Finally, as a partial check on the S G B and τ G I values, they are input to a Sentaurus device model, and the simulated performance is compared to the measured performance. The methodology developed here can be applied broadly to CdTe and CdSeTe thin-film technology and to other thin-film solar cell materials including Cu(In1-xGax)Se2, Cu2ZnSnS4, and perovskites.

Original languageAmerican English
Article number113104
Number of pages13
JournalJournal of Applied Physics
Issue number11
StatePublished - 21 Sep 2018

Bibliographical note

Publisher Copyright:
© 2018 Author(s).

NREL Publication Number

  • NREL/JA-5K00-71546


  • crystallographic defects
  • electrical properties and parameters
  • luminescence
  • scanning electron microscopy
  • semiconductors
  • solar cells
  • thin films


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