Molecular Quadrupole Moments Promote Ground‐State Charge Generation in Doped Organic Semiconductors - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Advanced Functional Materials Année : 2020

Molecular Quadrupole Moments Promote Ground‐State Charge Generation in Doped Organic Semiconductors

Giacomo Londi
Gabriele d'Avino
David Beljonne

Résumé

The role of local environmental interactions on the generation of free charge carriers in doped organic layers is investigated. Via a classical micro-elec-trostatic model, a dual effect of molecular quadrupole moments of host and dopant molecules on doping is demonstrated. Namely, electrostatic interactions ease ionization of the dopant by altering the energy level alignment between the host and the dopant and reduce the barrier for charge dissocia-tion by flattening the energy landscape around the ionized dopants. These results indicate that tailoring molecular quadrupole moments of the host and/or dopant are an attractive strategy toward improved doping efficiency in organic semiconductors. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.202004600. steps. [1b,4,5] The first step involves either a hybridization of the host-dopant frontier molecular orbitals or a ground-state integer charge transfer (CT) process between the host and the dopant. [1a,6] For p-type doping, the latter is favored when the energy difference between the ioni-zation potential (IP) of the host and the electron affinity (EA) of the dopant (i.e., the host-dopant gap Γ hd = IP host − EA dop) is smaller in magnitude than the Cou-lomb binding energy between an electron and its geminate hole sitting on nearest neighbor molecules (V eh). [7] In such conditions , a bound CT state with an electron added to the dopant and a hole left on the host molecule is generated. [7] This is the ionization step. The second step, namely, the charge dissociation, then consists of the spatial migration of the hole (for p-doping) away from the ionized acceptor that requires overcoming the Coulomb binding of the CT pair, which usually amounts to several hundreds of meV. [4a,8] The energetic and kinetic aspects of both steps need to be concomi-tantly optimized in order to maximize the overall charge generation efficiency, which calls for a control of the interactions between the molecules at the microscopic level. [3] Tuning these microscopic interactions can be achieved by molecular and material engineering. For instance, Warren et al. demonstrated that the energy levels in an organic semiconductor and the Fermi energy can be simultaneously tuned by taking advantage of molecular quadrupolar interactions. [1c] This result was achieved by co-evaporating a host mixture between zinc-phthalocyanine (ZnPc) and its eight times fluori-nated counterpart (F 8 ZnPc) together with the p-type dopant F6-TCNNQ. Such mixtures are very interesting because they provide an effective and practical approach to finely control the p-doping efficiency of F6-TCNNQ upon tuning the host energy levels, which are a function of the ZnPc:F 8 ZnPc molar ratio. [1c,9] Here, in the wake of the very recent experimental work reported by Warren et al., [1c] we investigate the role of environmental interactions on the charge generation mechanism in doped binary (ZnPc:F6-TCNNQ and F 8 ZnPc:F6-TCNNQ) and ternary (ZnPc:F 8 ZnPc:F6-TCNNQ) blends. Based on an in-depth atomistic modeling of electrostatic and dielectric phenomena in molecular solids, [10] we show that charge-quadrupole interactions affect both the ionization step (by reshuffling the energy levels of the dopant and the host) and the charge dissociation step (by creating a favorable energy pathway for the hole). Interestingly, in addition to long-range electrostatics phenomena characterizing the energy landscape of ordered molecular films, [10] we observe that the substitution
Fichier principal
Vignette du fichier
ms.pdf (1.21 Mo) Télécharger le fichier

Dates et versions

hal-03011441 , version 1 (03-12-2020)

Identifiants

Citer

Alberto Privitera, Giacomo Londi, Moritz Riede, Gabriele d'Avino, David Beljonne. Molecular Quadrupole Moments Promote Ground‐State Charge Generation in Doped Organic Semiconductors. Advanced Functional Materials, 2020, 30 (45), pp.2004600. ⟨10.1002/adfm.202004600⟩. ⟨hal-03011441⟩

Collections

UGA CNRS NEEL
26 Consultations
155 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More