Abstract
The electronic and optical properties of the paradigmatic F4TCNQ-doped pentacene in the low-doping limit are investigated by a combination of state-of-the-art many-body \emph{ab initio} methods accounting for environmental screening effects, and a carefully parametrized model Hamiltonian. We demonstrate that while the acceptor level lies very deep in the gap, the inclusion of electron-hole interactions strongly stabilizes dopant-semiconductor charge transfer states and, together with spin statistics and structural relaxation effects, rationalize the possibility for room-temperature dopant ionization. Our findings reconcile available experimental data, shedding light on the partial vs. full charge transfer scenario discussed in the literature, and question the relevance of the standard classification in shallow or deep impurity levels prevailing for inorganic semiconductors.
Highlights
Doping of organic semiconductors (OSC) [1,2] by introduction in the host matrix of strong electron- or holedonating molecules has been shown to increase their electrical conductivity by orders of magnitude, leading to enhanced performances in organic light-emitting devices and photovoltaic cells
Within our hybrid formalism, we describe a supramolecular complex (CPX) formed by one F4TCNQ molecule surrounded by its first shell of six pentacene neighbors (1 + 6 CPX ) at the GW/BSE level
This CPX is embedded into the pentacene crystal described within the charge response (CR) model [38,39], which provides an accurate description of the anisotropic static dielectric response of molecular crystals [39]
Summary
Doping of organic semiconductors (OSC) [1,2] by introduction in the host matrix of strong electron- or holedonating molecules has been shown to increase their electrical conductivity by orders of magnitude, leading to enhanced performances in organic light-emitting devices and photovoltaic cells. Focusing on the paradigmatic case of 2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (F4TCNQ) as a hole dopant in bulk pentacene (PEN, see Fig. 1) [4,15,16], it was shown that the introduction of the molecular dopant does not lead to any ultraviolet photoelectron spectroscopy (UPS) evidence of singly-occupied levels in the pentacene gap, as expected according to the standard polaronic picture for polymers [17]. Doping results instead in the emergence of two novel optical absorption lines at ∼1.2–1.4 eV, located below the 1.8 eV pentacene absorption
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