A team from Southern University of Science and Technology published a research paper titled "Unraveling the Interfacial Homogeneity and Bulk Crystallization for Efficient and Stable Perovskite Solar Cells via Ionic Liquids" in the journal Energy & Environmental Science. Xiaowei Xu is the first author, and Zhang Yong, Qiu Longbin, Xu Baomin, and Aung Ko Ko Kyaw are co-corresponding authors.
Key Highlights: This paper proposes a synergistic approach using ionic liquids to improve the uniformity of the SAM and its interaction with the underlying perovskite interface, while simultaneously modulating perovskite crystallization. The multifunctional ionic liquid tetramethylguanidine tetrafluoroborate (TMGBF4) was used as an additive to modulate the perovskite crystallization process, reduce trap defect density, and enhance the long-term stability of the perovskite film. A best-in-class power conversion efficiency of 26.18% (certified at 25.74%) was achieved, along with outstanding long-term operational stability of 1100 hours under continuous light stress at 65°C.
Despite improvements in the efficiency of inverse perovskite solar cells using self-assembled monolayers (SAMs), efficiency and stability challenges remain due to issues at the bottom interface and within the bulk perovskite. The SAM at the bottom interface is easily washed away by the overlying perovskite solvent, resulting in an uneven interface and thus impairing non-radiative recombination. Therefore, protecting the underlying SAM from perovskite solvent attack is a pressing issue for further improving the efficiency and stability of PSCs for commercialization.
To this end, Zhang Yong, Qiu Longbin, Xu Baomin, and Aung Ko Ko Kyaw from the Southern University of Science and Technology introduced an ionic liquid (IL) as a protective layer for the SAM, stabilizing its uniformity while passivating the bottom perovskite interface and aligning the interface energy levels. Furthermore, the ionic liquid tetramethylguanidine tetrafluoroborate (TMGBF4) was incorporated into the perovskite precursor solution to modulate perovskite crystallization. TMGBF4, with its electron-withdrawing and electron-donating properties, chemically passivates uncoordinated Pb2+ and halide vacancies through coordination and ionic bonding. This passivation reduces trap defect density and improves the long-term stability of the perovskite film. Due to the effects of these ionic liquids on both the bulk and interface, a best-in-class power conversion efficiency of 26.18% (certified at 25.74%) was achieved, along with excellent long-term operational stability of 1100 hours under continuous light stress at 65°C.
This study demonstrates a synergistic bulk-interface strategy for enhancing the performance and stability of perovskite solar cells using ionic liquids. It offers a new perspective for addressing interfacial energy inhomogeneity and provides valuable guidelines for modulating the crystallization process to improve the efficiency and stability of PSCs.
Source：DOI: 10.1039/D4EE05135A