The potential of transparent sputtered NaI:Tm2+, CaBr2:Tm2+, and CaI2:Tm2+ thin films as luminescent solar concentrators

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Abstract

The parameters governing the performance of a luminescent solar concentrator (LSC) are determined for sputtered thin-films of NaI:Tm2+, CaBr2:Tm2+, and CaI2:Tm2+. These parameters are determined by using six gradient thin film material libraries, combinatorially sputtered from metallic and pressed powder targets. These films show strong 4f13→4f12d1 absorption of maximally 752 cm−1 at.%−1 for NaI:Tm2+, 31 cm−1 at.%−1 for CaBr2:Tm2+, and 473 cm−1 at.%−1 for CaI2:Tm2+. This absorption covers the entire visible spectrum and does not overlap with the infrared 4f-4f emission at 1140 nm. Decay measurements are used to estimate the quantum yields of the thin-films. These quantum yields can be as high as 44 % for NaI:Tm2+, when doped with 0.3 at.% Tm. Even at doping percentages as low as 0.3 at.%, the films appear to show luminescence quenching. The concentration-dependent absorption and quantum yield are combined with the index of refraction, resolved from transmission measurements, to simulate the optical efficiency of a thin film Tm2+-doped halide LSC. These simulations show that LSCs based on Tm2+ can display excellent color rendering indices of up to 99 %, and neutral color temperatures, between 4500K and 6000K. Under optimal conditions, thin-films constrained to a thickness of 10μm and 80 % transmission of the visible spectrum, would be able to display optical efficiencies of 0.71 %. This optical efficiency compares favorably to the maximally achievable 3.5 % under these constraints. This efficiency is largely independent of the size of LSC itself.

Original languageEnglish
Article number110944
Number of pages10
JournalSolar Energy Materials and Solar Cells
Volume223
DOIs
Publication statusPublished - 2021

Keywords

  • Building-integrated photovoltaics
  • Combinatorial science
  • Halide
  • Luminescent solar concentrator
  • Optical simulation
  • Sputter deposition

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