Here, Moungi G. Bawendi et al. from MIT present a reliable noble metal-free synthesis of Spiro-MeOTAD (TFSI ) 4, which is used as an oxidant. No additives were added to the partially oxidized Spiro-MeOTAD hole transport layer. The device efficiency reached up to 24.2%. The conductivity was largely generated by the first 1% of oxidation. Further oxidation moved the energy levels away from the vacuum level, allowing the energy level arrangement to be tuned without the use of additives, which contradicts the current understanding of the system.
In the absence of additives, the device stability was significantly improved after 1400 hours of continuous illumination under one sun at high temperatures up to 85°C. The remaining degradation was pinpointed as ion migration and reaction in the perovskite layer, which can be further suppressed by compositional engineering and adequate ion blocking layers.
M. J. Grotevent, Y. Lu, T. Šverko, M.-C. Shih, S. Tan, H. Zhu, T. Dang, J. K. Mwaura, R. Swartwout, F. Beiglböck, L. Kothe, V. Bulović, M. G. Bawendi, Additive-Free Oxidized Spiro-MeOTAD Hole Transport Layer Significantly Improves Thermal Solar Cell Stability. Adv. Energy Mater. 2024, 2400456.
https://doi.org/10.1002/aenm.202400456