American Chemical Society
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Analyzing the n‑Doping Mechanism of an Air-Stable Small-Molecule Precursor

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journal contribution
posted on 2017-12-13, 00:00 authored by Martin Schwarze, Benjamin D. Naab, Max L. Tietze, Reinhard Scholz, Paul Pahner, Fabio Bussolotti, Satoshi Kera, Daniel Kasemann, Zhenan Bao, Karl Leo
Efficient n-doping of organic semiconductors requires electron-donating molecules with small ionization energies, making such n-dopants usually sensitive to degradation under air exposure. A workaround consists in the usage of air-stable precursor molecules containing the actual n-doping species. Here, we systematically analyze the doping mechanism of the small-molecule precursor o-MeO-DMBI-Cl, which releases a highly reducing o-MeO-DMBI radical upon thermal evaporation. n-Doping of N,N-bis­(fluoren-2-yl)-naphthalene tetracarboxylic diimide yields air-stable and highly conductive films suitable for application as electron transport layer in organic solar cells. By photoelectron spectroscopy, we determine a reduced doping efficiency at high doping concentrations. We attribute this reduction to a change of the precursor decomposition mechanism with rising crucible temperature, yielding an undesired demethylation at high evaporation rates. Our results do not only show the possibility of efficient and air-stable n-doping, but also support the design of novel air-stable precursor molecules of strong n-dopants.