Minority Carrier Electron Traps in CZTSSe Solar Cells Characterized by DLTS and DLOS

Carolyn Beall, Ingrid Repins, V. Kheraj, E. Lund, A. Caruso, K. Al-Ajmi, D. Pruzan, C. Miskin, R. Agrawal, M. Scarpulla

Research output: Contribution to conferencePaperpeer-review

3 Scopus Citations


We report observations of minority carrier interactions with deep levels in 6-8% efficient Cu2ZnSn(S, Se)4 (CZTSSe) devices using conventional and minority deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS). Directly observing defect interactions with minority carriers is critical to understanding the recombination impact of deep levels. In devices with Cu2ZnSn(S, Se)4 nanoparticle ink absorber layers we identify a mid-gap state capturing and emitting minority electrons. It is 590±50 meV from the conduction band mobility edge, has a concentration near 1015/cm3, and has an apparent electron capture cross section ∼10-14 cm2. We conclude that, while energetically positioned nearly-ideally to be a recombination center, these defects instead act as electron traps because of a smaller hole cross-section. In CZTSe devices produced using coevaporation, we used minority carrier DLTS on traditional samples as well as ones with transparent Ohmic back contacts. These experiments demonstrate methods for unambiguously probing minority carrier/defect interactions in solar cells in order to establish direct links between defect energy level observations and minority carrier lifetimes. Furthermore, we demonstrate the use of steady-state device simulation to aid in the interpretation of DLTS results e.g. to put bounds on the complimentary carrier cross section even in the absence its direct measurement. This combined experimental and theoretical approach establishes rigorous bounds on the impact on carrier lifetime and Voc of defects observed with DLTS as opposed to, for example, assuming that all deep states act as strong recombination centers.

Original languageAmerican English
Number of pages5
StatePublished - 18 Nov 2016
Event43rd IEEE Photovoltaic Specialists Conference, PVSC 2016 - Portland, United States
Duration: 5 Jun 201610 Jun 2016


Conference43rd IEEE Photovoltaic Specialists Conference, PVSC 2016
Country/TerritoryUnited States

Bibliographical note

Publisher Copyright:
© 2016 IEEE.

NREL Publication Number

  • NREL/CP-5K00-67948


  • admittance
  • decision support systems
  • photovoltaic cells
  • photovoltaic systems
  • spectroscopy


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