The concept of using redox-active ligands is often considered from ‘their effect on the metal center properties’ point of view. We present the reverse side of this approach – change of redox properties of ligands under the influence of metal.
At present, the use of low-valent derivatives of the
main group
elements, including metallylenes, etc., in catalysis as an alternative
to transition metals is widely discussed. The high reactivity of these
compounds often requires their stabilization by using electron-pair
donor ligands. The influence of the latter on oxidative addition reactions
is usually not considered. In this work, to the best of our knowledge
for the first time, using the example of the oxidative insertion of
Lappert’s germylene into PhSSPh in the presence of N, S, P,
and O donor ligands, we show that the ligands significantly increase
the reaction rate. This can be associated with an increase in the
level of the germylene highest occupied molecular orbital under the
influence of a donor. Qualitatively, the obtained values of the reaction
rate constants correlate well with the germylene oxidation potentials
in the presence of ligands or ligand oxidation potentials.
Inverted perovskite solar cells with a p-i-n configuration have attracted considerable attention from the research community because of their simple design, insignificant hysteresis, improved operational stability, and low-temperature fabrication technology. However, this type of device is still lagging behind the classical n-i-p perovskite solar cells in terms of its power conversion efficiency. The performance of p-i-n perovskite solar cells can be increased using appropriate charge transport and buffer interlayers inserted between the main electron transport layer and top metal electrode. In this study, we addressed this challenge by designing a series of tin and germanium coordination complexes with redox-active ligands as promising interlayers for perovskite solar cells. The obtained compounds were characterized by X-ray single-crystal diffraction and/or NMR spectroscopy, and their optical and electrochemical properties were thoroughly studied. The efficiency of perovskite solar cells was improved from a reference value of 16.4% to 18.0–18.6%, using optimized interlayers of the tin complexes with salicylimine (1) or 2,3-dihydroxynaphthalene (2) ligands, and the germanium complex with the 2,3-dihydroxyphenazine ligand (4). The IR s-SNOM mapping revealed that the best-performing interlayers form uniform and pinhole-free coatings atop the PC61BM electron-transport layer, which improves the charge extraction to the top metal electrode. The obtained results feature the potential of using tin and germanium complexes as prospective materials for improving the performance of perovskite solar cells.
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