Additive‐Free Oxidized Spiro‐MeOTAD Hole Transport Layer Significantly Improves Thermal Solar Cell Stability

Journal Article · 06 June 2024 · Advanced Energy Materials

DOI: https://doi.org/10.1002/aenm.202400456 · OSTI ID:2429740

Grotevent, Matthias J.  ^[1]; Lu, Yongli ^[1]; Šverko, Tara ^[1]; Shih, Meng‐Chen ^[1]; Tan, Shaun ^[1]; Zhu, Hua ^[1]; Dang, Tong ^[2]; Mwaura, Jeremiah K. ^[3]; Swartwout, Richard ^[4]; Beiglböck, Finn ^[5]; Kothe, Linda ^[6]; Bulović, Vladimir ^[2]; Bawendi, Moungi G.  ^[1]

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1. Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
2. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
3. Research Laboratory of Electronics Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
4. Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA, Active Surfaces 444 Somerville Ave Somerville MA 02143 USA
5. Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA, ETH Zurich Zürich 8092 Switzerland
6. Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA, Paderborn University 33098 Paderborn Germany

Abstract Perovskite solar cells are among the most promising new solar technologies, already surpassing polycrystalline silicon solar cell efficiencies. The stability of the highest efficiency devices at elevated temperature is, however, poor. These cells typically use Spiro‐MeOTAD as the hole transporting layer. It is generally believed that additives, required for enhancing electrical conductivity and optimizing energy level alignment, are responsible for the reduced stability—inferring that Spiro‐MeOTAD based hole transporting layers are intrinsically unstable. Here, a reliable noble metal free synthesis of Spiro‐MeOTAD (bis(trifluoromethane)sulfonimide) ₄ is presented which is used as the oxidizing agent. No additives are added to the partially oxidized Spiro‐MeOTAD hole‐transporting layer. Device efficiencies up to 24.2% are achieved. Electrical conductivity is largely developed by the first 1% oxidation. Further oxidation shifts the energy levels away from the vacuum level, which allows tuning of the energy level alignment without the use of additives—contradicting the current understanding of this system. Without additives, devices demonstrate significant improvement in stability at elevated temperatures up to 85 °C under one sun over 1400 h continuous illumination. The remaining degradation is pinpointed to ion migration and reactions in the perovskite layer which may be further suppressed with compositional engineering and adequate ion barrier layers.

• Sponsoring Organization: USDOE
• Grant/Contract Number: NONE; EE0009512; SC0021650
• OSTI ID: 2429740
• Journal Information: Advanced Energy Materials, Journal Name: Advanced Energy Materials Journal Issue: 31 Vol. 14; ISSN 1614-6832
• Publisher: Wiley Blackwell (John Wiley & Sons)Copyright Statement
• Country of Publication: Germany
• Language: English