A Molybdenum Dithiolene Complex asp-Dopant for Hole-Transport Materials: A Multitechnique Experimental and Theoretical Investigation

Abstract

Molybdenum tris-[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd) 3 ) is investigated as a p-dopant for organic semiconductors. With an electron affinity of 5.6 eV, Mo(tfd) 3 is a strong oxidizing agent suitable for the oxidation of several hole transport materials (HTMs). Ultraviolet photoemission spectroscopy confirms p-doping of the standard HTM N,. Strong enhancement of hole injection at R-NPD/Au interfaces is achieved via doping-induced formation of a narrow depletion region in the organic semiconductor. Variable-temperature current-voltage measurements on R-NPD: Mo(tfd) 3 (0-3.8 mol %) yield an activation energy for polaron transport that decreases with increasing doping concentration, which is consistent with the effect of the doping-induced filling of traps on hopping transport. Good stability of Mo(tfd) 3 versus diffusion in the R-NPD host matrix is demonstrated by Rutherford backscattering for temperatures up to 110°C. Density functional theory (DFT) calculations are performed to obtain geometries and electronic structures of isolated neutral and anionic Mo(tfd) 3 molecules.

Toward a comprehensive understanding of molecular doping organic semiconductors (review)

“…Importantly, for high dopant concentrations, while the spectra still retain all features of pristine CuPc without indications for polaronic states, the authors observe a new occupied state in the fundamental gap of CuPc fully separated from E F (highlighted in yellow in Figure 7d), which they label as "gap state" and suggest to be due to the formation of charge transfer complexes. Figure 7d [167,168], lend further credence to the generality of CPX formation and the concomitant energetic splitting of the resulting SMHOs in molecularly-doped COM films [131,166,169]. Note that in a related study by Kahn et al [170], where ZnPc was blended with 30% of F 4 TCNQ ( Figure 6 in Ref.…”

Comparison of solution-mixed and sequentially processed P3HT:F4TCNQ films: effect of doping-induced aggregation on film morphology

“…9 shows 3 is somewhat surprising, as it is considerably bulkier than the planar structure of F4TCNQ, and is only sparingly soluble in most common solvents. 29,30,32 These results suggest that sequential doping is widely applicable to other polymer:dopant systems. In addition, after doping, these films are essentially insoluble in their casting solvents.…”

“…[20][21][22][23][24] Several groups have synthesized and studied alternative molecular dopants in an effort to increase the thermal stability of doped films. 21,[25][26][27][28][29][30][31][32] Finally, a less commonly discussed but equally problematic issue lies in solution processing doped films. Several groups have noted that doping often results in drastically reduced solubility of polymers; as a result, mixed polymer:dopant solutions must be kept at high temperatures and dilute concentrations, and tend to rapidly aggregate, forming gels or large particles.…”

Enhancement of photoresponsive electrical characteristics of multilayer MoS2 transistors using rubrene patches

“…2). In other previous reports, the interfacial CT doping induced filling of the surface charge traps and contributed to the accumulation of mobile charge carriers at the channels [29,30]. In addition, the poor device performance such as phononlimited low mobility could be improved through Schottky barrier lowering caused by the CT doping in the thin dielectric layer even in the presence of non-ideal channel/dielectric interfaces [33].…”

“…This process induced extra free electrons at the conduction band edge of MoS 2 , and thus the activation energy in the MoS 2 channel could be reduced [28]. In previous reports for molybdenum dithiolene complexes with a p-type organic material dopant, the formation of a narrow depletion region in the channel material by charge doping induced a variation in the charge transport properties [29,30]. The charge doping effect on the monolayer MoS 2 using Au nanoparticles was also reported [31].…”