Ultrafast pump-probe reflectance spectroscopy: Why sodium makes Cu(In,Ga)Se2 solar cells better

Jessica Eid, Anwar Usman, Issam Gereige, Jeroen Van Duren, Vadim Lyssenko, Karl Leo, Omar F. Mohammed

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Although Cu(In,Ga)Se2 (CIGS) solar cells have the highest efficiency of any thin-film solar cell, especially when sodium is incorporated, the fundamental device properties of ultrafast carrier transport and recombination in such cells remain not fully understood. Here, we explore the dynamics of charge carriers in CIGS absorber layers with varying concentrations of Na by femtosecond (fs) broadband pump-probe reflectance spectroscopy with 120 fs time resolution. By analyzing the time-resolved transient spectra in a different time domain, we show that a small amount of Na integrated by NaF deposition on top of sputtered Cu(In,Ga) prior to selenization forms CIGS, which induces slower recombination of the excited carriers. Here, we provide direct evidence for the elongation of carrier lifetimes by incorporating Na into CIGS.
Original languageEnglish (US)
Pages (from-to)33-37
Number of pages5
JournalSolar Energy Materials and Solar Cells
StatePublished - Apr 14 2015

ASJC Scopus subject areas

  • Surfaces, Coatings and Films
  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment


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