Bandgap Optimization for Bifacial Tandem Solar Cells

Lujia Xu*, Fuzong Xu, Jiang Liu, Xuechun Zhang, Anand Selvin Subbiah, Stefaan De Wolf*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Bifacial tandem solar cells can generate more power than their monofacial counterparts by exploiting albedo at their rear. Optimum bandgap (Eg) values for subcells in both two-terminal (2T) and four-terminal (4T) bifacial tandems under different albedos are discussed using radiative-recombination-limit calculations. Our investigation considers both AM1.5G and field spectra, incident on silicon-constrained and unconstrained tandems. We find that for an albedo in the 0.2-0.5 range for 2T tandems and ≥0.3 for 4T tandems, the optimal bottom Eg is ∼1.12 eV, indicating that silicon, besides practical purposes, can also theoretically be the best bottom cell. Furthermore, our work highlights that the 4T configuration may be more attractive than its 2T counterpart for bifacial deployment due to a higher theoretical energy yield with lower sensitivities to albedo variations. To maximize 2T-tandem power conversion efficiency, counterintuitively, rather than precise current matching, the subcell with the highest fill factor needs to be current-limiting.

Original languageEnglish (US)
Pages (from-to)3114-3121
Number of pages8
JournalACS Energy Letters
Issue number7
StatePublished - Jul 14 2023

Bibliographical note

Publisher Copyright:
© 2023 American Chemical Society.

ASJC Scopus subject areas

  • Chemistry (miscellaneous)
  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Materials Chemistry


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