The Beet Technology

Beet Inc. absorber-materials platform addresses limitations of traditional single-junction cells, e.g. Si, CdTe, CIGS and CZTS, by enabling high-efficiency, inexpensive mechanically stacked tandem devices. Beet will provide proprietary polycrystalline, thin-film absorbers integrated into solar cells that achieve:

  • photovoltaic conversion efficiencies approaching 30%
  • lower module and BOS cost towards grid parity
  • scalability to high-volume manufacturing (>1TW) using sustainable materials and established processes requiring minimizing capital investment.

The selection of the C5S family as thin film solar cell (TFSC) absorbers is based on a functionality defined selection process originating from research within the Center for Inverse Design, a Department of Energy funded Energy Frontier Research Center. The selected best-of-class materials with the Cu3MCh4 (M=P,As,Sb; Ch=S,Se) exhibit rapid onset to high absorption, compared to existing commercial absorbers. Beet's devices have an electrostatic potential present across the entire absorber layer aiding effective extraction of photogenerated carriers, or drift-based operation, instead of the traditional diffusion-based (random motion) transport used in today's solar cell. The built-in drift field drives photogenerated carriers towards their contacts reducing constrains placed on carrier mobilities and minority carrier lifetimes.

Beet Inc. (has applied for a patent) and holds an exclusive license option with Oregon State University for field of use technology rights. The current objective is to demonstrate conversion efficiency in the lab-scale single-junction devices using technology platform absorbers Cu3SbS4 and Cu3AsS4: two members of the new family of absorbers known as C5S. 


The C5S Technology


Information regarding the science and technology behind the C5S technology can be found below:


  • L. Yu, R. S. Kokenyesi, D. A. Keszler, and A. Zunger, “Inverse design of high absorption thin-film photovoltaic materials,” Advanced Energy Materials, vol. 3, pp. 43 – 48, 2013. 
    download paper

  • V. Itthibenchapong, R. S. Kokenyesi, A. J. Ritenour, L. N. Zakharov, S. W. Boettcher, J. F. Wager and D. A. Keszler, "Earth-abundant Cu-based chalcogenide semiconductors as photovoltaic absorbers", Journal of Materials Chemistry C, vol. 1, pp. 657-662, 2013.
    download paper

  • R. Kokenyesi, "Cu3-V-VI4 Thin Film Absorbers: Intrinsic Defects, Electrical Transport and Optical Absorption", Talk presented at MRS Fall 2013
    download abstract and presentation

  • R. Kokenyesi, "Earth-Abundant Inorganic Materials for Photovoltaic Conversion: Design and Potential", Invited talk presented at MRS Spring 2014.
    download abstract and presentation


Device Simulation of C5S-based thin-film solar cells


Optical and electrical properties of C5S-based thin films were used as inputs to a solar cell simulation software package (SCAPS) to assess photovoltaic behavior of C5S-based thin-film solar cells:


  • R. Ravichandran, "Device simulations of ultra-thin Cu-V-VI absorbers", poster presented at MRS Fall 2013
    download abstract and poster

  • R. Ravichandran, "Relationship between Absorber Layer Properties and Device Operation Modes for High Efficiency Thin Film Solar Cells", poster presented at APS Spring 2013
    download abstract and poster

  • R. Ravichandran, "Development of high efficiency solar absorbers", PhD thesis, 2014
    download thesis