Conductivity and Photoconductivity of a p-Type Organic Semiconductor under Ultrastrong Coupling

Kalaivanan Nagarajan , Jino George , Anoop Thomas , Eloise Devaux , Thibault Chervy , Stefano Azzini , Kripa Joseph , Abdelaziz Jouaiti (1) , Mir Hosseini , Anil Kumar , Cyriaque Genet , Nicola Bartolo , Cristiano Ciuti , Thomas Ebbesen

1 CMC - Chimie de la matière complexe

During the last decade, it has been shown that light-matter strong coupling of materials can lead to modified and often improved properties which has stimulated considerable interest. While charge transport can be enhanced in n-type organic semiconductors by coupling the electronic transition and thereby splitting the conduction band into polaritonic states, it is not clear whether the same process can also influence carrier transport in the valence band of p-type semiconductors. Here we demonstrate that it is indeed possible to enhance both the conductivity and photoconductivity of a p-type semiconductor rr-P3HT that is ultra-strongly coupled to plasmonic modes. It is due to the hybrid light-matter character of the virtual polaritonic excitations affecting the linear-response of the material. Furthermore, in addition to being enhanced, the photoconductivity of rr-P3HT shows modified spectral response due to the formation of the hybrid polaritonic states. This illustrates the potential of engineering the vacuum electromagnetic environment to improve the opto-electronic properties of organic materials. Light-matter strong coupling is a promising approach for controlling properties of matter. 1-29 For instance, it has been shown that charge transport can be enhanced by an order of magnitude in the 2n-type perylene di-imide family of compounds and that the rate of energy transfer can be boosted, leading to nearly unit transfer efficiency. 11-18 Furthermore, energy transfer can even be achieved over distances well beyond what is expected from Förster theory by entangling donor and acceptor to the same cavity mode. 16-18 The modification of magneto-transport properties, with a reduction in the longitudinal resistance, has recently been predicted 30 and reported for an ultra-strongly coupled 2D electron gas. 31 The improved transport properties of organic materials in the strong coupling regime are the result of the delocalized character of the collective states generated from the excited states or the conduction band in the case of n-type semiconductors. However, the role of hybrid light-matter states on the transport characteristics of p-type semiconductors, where valence band holes are the majority carriers have not yet been studied, although it is also potentially important for organic electronics. 32-38 Interestingly, based on the theory of intersubband cavity polaritons, 38 one can predict that when excitons are coupled to a confined optical mode and one reaches the ultra-strong coupling regime, the ground state shifts while acquiring polaritonic character (cf. Supporting Information (SI)). The fundamental question we explore here is whether this polaritonic character of the ground state and its excitations leads to enhanced conductivity in p-type semiconductors. For that purpose, we have studied a well-known p-type semiconductor, the regio-regular poly-(3-hexylthiophene) (rr-P3HT) whose structure is shown in Figure 1a. Since photoconductivity plays a fundamental role in many technological applications such as photodetectors, electrostatic imaging and photovoltaics, 39-45 we also explore whether the photoconductivity can also be improved in the ultrastrong coupling regime.

Mots clés: strong coupling; organic semiconductors; conductivity; photoconductivity; p-type

Domaines: Chimie

Kalaivanan Nagarajan, Jino George, Anoop Thomas, Eloise Devaux, Thibault Chervy, et al.. Conductivity and Photoconductivity of a p-Type Organic Semiconductor under Ultrastrong Coupling. ACS Nano, 2020, 14 (8), pp.10219-10225. ⟨10.1021/acsnano.0c03496⟩. ⟨hal-03003326⟩