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

• Published in: ACS applied materials & interfaces 2018-01, Vol.10 (1), p.1340-1346
• Main Authors: Schwarze, Martin, Naab, Benjamin D, Tietze, Max L, Scholz, Reinhard, Pahner, Paul, Bussolotti, Fabio, Kera, Satoshi, Kasemann, Daniel, Bao, Zhenan, Leo, Karl
• Format: Article
• Language: English
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.7b14034

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.