Molecular doping is now increasingly used to control the electronic and electrical properties of
organic semiconductors, lower contact resistance, enhance bulk conductivity and carrier mobility,
and create higher performance devices. In this talk, I review processes and options for bulk and
interface doping in molecular and polymer semiconductors, and the roles electron spectroscopy and
carrier transport measurements play in defining key issues. Recent results on p- and n-doping are
described. P-doping using 2,2′-(perfluoronaphthalene-2,6-diylidene)dimalononitrile (F6-TCNNQ)
is tested on two relatively challenging hole transport materials, 2,2′,7,7′-Tetrakis(N,Ndiphenylamino)-
9,9-spirobifluorene (Spiro-TAD) and tris(4-carbazoyl-9-ylphenyl)amine (TCTA)
[1]. The full electronic parameters of these molecules are determined via combinations of electron
spectroscopies. Temperature-dependent transport measurements are done to establish film
conductivity and hole hopping activation energy as a function of dopant concentration. We then
turn to the challenge of n-doping very low electron affinity (EA) electron transport layers (ETL), an
issue critical to OLEDs. We look at the air-stable dimer of (pentamethylcyclopentadienyl)(1,3,5-
trimethylbenzene)ruthenium ([RuCp*Mes]2) [2], and use it to n-dope phenyldi(pyren-2-
yl)phosphine oxide (POPy2) (EA = 2.1 eV). We demonstrate that photo-activation of the cleavable
dimeric dopant results in kinetically stable and efficient n-doping of the host semiconductor, whose
reduction potential is beyond the thermodynamic reach of the dimer’s effective reducing strength
[3]. We demonstrate the use of this doped ETL to fabricate high-efficiency organic light-emitting
diodes.
[1] F. Zhang and A. Kahn, Adv. Funct. Mat. 28, 1703780 (2018)
[2] G. Song, S.-B. Kim, S. Mohapatra, Y. Qi, T. Sajoto, A. Kahn, S. R. Marder and S.
Barlow, Adv. Mat. 24, 699 (2012)
[3] X. Lin, B. Wegner, K. M. Lee, M. Fusella, F. Zhang, K. Moudgil, S. Barlow, S. R.
Marder, N. Koch and A. Kahn, Nature Materials, 16, 1209 (2017)
