Monolithic Thin-Film Chalcogenide-Silicon Tandem Solar Cells Enabled by a Diffusion Barrier

Alireza Hajijafarassar, Filipe Martinho, Andrea Crovetto, Jørgen Schou, Ole Hansen

Research output: Contribution to conferenceConference abstract for conferenceResearchpeer-review


Following the recent success of monolithically integrated Perovskite/Si tandem solar cells, there has been a surge of interest in alternative wide bandgap top-cell materials with prospects of a fully earth-abundant, stable and efficient tandem solar cell. Thin film chalcogenides such as Cu2ZnSnS4 (CZTS, 1.6
eV band gap) or Cu2BaSnS4 (CBTS, 2.0 eV band gap) could be suitable candidates. However, this class of materials has 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 and CBTS on a Si bottom solar cell. A simple double-sided Tunnel Oxide Passivated Contact (TOPCon) structure is used as bottom cell, and a thin TiN layer is selected as both a diffusion barrier and a recombination layer between the two sub-cells. We show that TiN successfully mitigates in-diffusion of CZTS elements into the c-Si bulk during the high temperature sulfurization process, and 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 the first proof-of-concept twoterminal CZTS/Si and CBTS/Si tandem devices with a efficiencies up to 3.3%. 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
Publication date2019
Publication statusPublished - 2019
Event2019 MRS Fall Meeting - Boston, United States
Duration: 1 Dec 20196 Dec 2019


Conference2019 MRS Fall Meeting
CountryUnited States

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