Monolithic thin-film chalcogenide–silicon tandem solar cells enabled by a diffusion barrier

Alireza Hajijafarassar*, Filipe Mesquita Alves Martinho, Fredrik Stulen, Sigbjørn Grini, Simón López Mariño, Moises Espindola Rodriguez, Max Döbeli, Stela Canulescu, Eugen Stamate, Mungunshagai Gansukh, Sara Lena Josefin Engberg, Andrea Crovetto, Lasse Vines, Jørgen Schou, Ole Hansen

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, great interest has been raised in searching for alternative wide bandgap top-cell materials with prospects of a fully earth-abundant, stable and efficient tandem solar cell. Thin film chalcogenides (TFCs) such as the Cu2ZnSnS4 (CZTS) could be suitable top-cell materials. However, TFCs have the disadvantage that generally at least one high temperature step (>500 °C) is needed during the synthesis, which could contaminate the Si bottom cell. Here, we systematically investigate the monolithic integration of CZTS on a Si bottom solar cell. A thermally resilient double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell. A thin (<25 nm) TiN layer between the top and bottom cells, doubles as diffusion barrier and recombination layer. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and find no evidence of electrically active deep Si bulk defects in samples protected by just 10 nm TiN. Post-process minority carrier lifetime in Si exceeded 1.5 ms, i.e., a promising implied open-circuit voltage (i-Voc) of 715 mV after the high temperature sulfurization. Based on these results, we demonstrate a first proof-of-concept two-terminal CZTS/Si tandem device with an efficiency of 1.1% and a Voc of 900 mV. A general implication of this study is that the growth of complex semiconductors on Si using high temperature steps is technically feasible, and can potentially lead to efficient monolithically integrated two-terminal tandem solar cells.
Original languageEnglish
Article number110334
JournalSolar Energy Materials and Solar Cells
Number of pages11
Publication statusPublished - 2020


  • Tandem
  • Photovoltaric
  • Silicon
  • TOPCon
  • CZTS
  • Titanium nitride


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