NiOx Nanoparticles Enable Ultrafast Activation of the Spiro-OMeTAD Hole Transport Layer for High-Performance and Stable Perovskite Solar Cells

Weina Zhang^a, Ludmila Cojocaru^b, Haruko Tamegai^a, Satoshi Uchida^a, Jotaro Nakazaki^c, Hiroshi Segawa^a

^aResearch Center for Advanced Science and Technology, The University of Tokyo

^bKomaba Institute for Science, Graduate School of Arts and Sciences, The University of Tokyo, Japan

^cKomaba Organization for Educational Excellence (KOMEX), College of Arts and Sciences, The University of Tokyo

Proceedings of MATSUS Fall 2026 Conference (MATSUSFall26)

A5 Interface Engineering, Optical Strategies and Multijunction Designs in Perovskite Photovoltaics and Optoelectronics

Palma, Spain, 2026 October 26th - 30th

Organizer: Monika Rai

Oral, Weina Zhang, presentation 359
Publication date: 22nd July 2026

The hole transport layer (HTL) plays a critical role in charge extraction and operational stability in n–i–p perovskite solar cells (PSCs). Spiro-OMeTAD remains the most widely used HTL; however, its conductivity relies on Li-TFSI and 4-tert-butylpyridine (tBP) additives and a slow oxygen-induced oxidation process that typically requires several days to complete.[1] Moreover, the presence of tBP compromises the thermal and environmental stability of the HTL, limiting both device durability and manufacturing efficiency. Developing charge transport layer engineering strategies that simultaneously accelerate HTL activation and improve stability remains an important challenge.[2-5]

Here, we report a tBP-free HTL engineering strategy by incorporating oleyl amine (OAm) coated nickel oxide nanoparticles (oil-NiO_x NPs) into the Spiro-OMeTAD/Li-TFSI system. The oil-NiO_x NPs promote homogeneous Li-TFSI dispersion and chemically interact with Li-TFSI to generate Ni³⁺ species, which efficiently oxidize Spiro-OMeTAD without prolonged air exposure. As a result, the HTL activation time is dramatically reduced from approximately 72 h to only 3 s, providing a simple and manufacturing-compatible route for rapid device fabrication.

Perovskite solar cells employing the oil-NiO_x NP-engineered HTL exhibit an initial power conversion efficiency (PCE) of 22.05%, which further increases to 24.20% after 72 h, outperforming conventional tBP-containing devices (12.49% initially and 23.52% after oxidation). More importantly, the elimination of tBP substantially improves operational stability, with the optimized devices retaining 94%, 61%, and 80% of their initial efficiency after 800 h under 55% relative humidity, 85 °C thermal stress, and continuous illumination, respectively.

This work demonstrates an effective charge transport layer engineering strategy that enables ultrafast HTL activation while simultaneously improving device efficiency, environmental stability, and processing compatibility. The proposed tBP-free approach provides a scalable pathway toward reliable, high-performance perovskite photovoltaics.

References:

[1] Lin, F.; Luo, J.; Zhang, Y.; Zhu, J.; Malik, H. A.; Wan, Z.; Jia, C.; Perovskite Solar Cells: Li–TFSI and t-BP-based Chemical Dopant Engineering in Spiro-OMeTAD, J. Mater. Chem. A 2023, 11, 2544–2567.

[2] Jeon, I.; Ueno, H.; Seo, S.; Aitola, K.; Nishikubo, R.; Saeki, A.; Okada, H.; Boschloo, G.; Maruyama, S.; Matsuo, Y.; Lithium-Ion Endohedral Fullerene (Li+@C60) Dopants in Stable Perovskite Solar Cells Induce Instant Doping and Anti-Oxidation, Angew. Chem. Int. Ed. 2018, 57, 4607–4611.

[3] Liu, Y.; Hu, Y.; Zhang, X.; Zeng, P.; Li, F.; Wang, B.; Yang, Q.; Liu, M.; Inhibited Aggregation of Lithium Salt in Spiro-OMeTAD Toward Highly Efficient Perovskite Solar Cells, Nano Energy 2020, 70, 104483.

[4] Yang, Y.; Wu, J.; Liu, X.; Guo, Q.; Wang, X.; Liu, L.; Ding, Y.; Dai, S.; Lin, J.-Y.; Dual Functional Doping of KMnO4 in Spiro-OMeTAD for Highly Effective Planar Perovskite Solar Cells, ACS Appl. Energy Mater. 2019, 2, 2188–2196.

[5] Wang, X.; Wu, J.; Yang, Y.; Liu, X.; Guo, Q.; Song, Z.; Li, G.; Lan, Z.; Huang, M.; High Performance and Stable Perovskite Solar Cells Using Vanadic Oxide as A Dopant for Spiro-OMeTAD, J. Mater. Chem. A 2019, 7, 13256–13264.

Acknowledgements:

This work is supported by the New Energy and Industrial Technology Development Organization (NEDO, Japan), Green Innovation Project, Development of Manufacturing Technology for Ultra-lightweight R2R Solar Cells.

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