3 years ago

Analyzing the n-Doping Mechanism of an Air-Stable Small-Molecule Precursor

the n-Doping Mechanism of an Air-Stable Small-Molecule Precursor
Paul Pahner, Benjamin D. Naab, Max L. Tietze, Zhenan Bao, Satoshi Kera, Reinhard Scholz, Daniel Kasemann, Karl Leo, Fabio Bussolotti, Martin Schwarze
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.

Publisher URL: http://dx.doi.org/10.1021/acsami.7b14034

DOI: 10.1021/acsami.7b14034

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