2D Colloidal Nanoplatelets based Optoelectronics
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2D Colloidal Nanoplatelets based Optoelectronics Adrien Robin1,2*, Emmanuel Lhuillier3, Benoit Dubertret2 1 Nexdot, 10 rue Vauquelin, Paris, France 2 Laboratoire de Physique et d’Etude des Matériaux, ESPCI ParisTech, PSL Research University, Sorbonne Université UPMC Université Paris 06, CNRS, 10 rue Vauquelin 75005 Paris, France. 3 Institut des Nanosciences de Paris, UPMC-CNRS UMR 7588, 4 place Jussieu, boîte courrier 840, 75252 Paris cedex 05, France. * To whom correspondence should be addressed: [email protected] ABSTRACT Two-Dimensional materials open up great prospects in photodetector applications owing to their sharp optical properties and the ability to combine them in layered heterostructures. Among this new class of materials, colloidal nanoplatelets (NPL) made of cadmium chalcogenides readily combine the thickness control at the atomic level together with the large scale production and ease of processing of colloidal materials. As a strategy to overcome the limited mobility inherent to nanocrystal based devices, the photocarrier lifetime is increased by building an electrolyte-gated phototransistor to passivate the electron traps. NPL can also be coupled with a graphene transport layer collecting the photogenerated charges, thus bypassing the transport bottleneck. We show that the charge transfer is driven by the large exciton binding energy of the NPL, which can be engineered by heterostructured NPL. This allows us to control the magnitude and the direction of the charge transfer to graphene. Eventually, we use nanotrench electrodes to decrease the transit time of the carriers, suppress the influence of film defects and provide an electric field large enough to overcome the large exciton binding energy of NPL. INTRODUCTION Over the past decade, the rise of graphene attracted a huge interest on 2D materials. Compared to conventional materials used in optoelectronics, they combine several advantages such as their small dimensions for higher integration, a high carrier mobility as well as higher surface sensitivity. The latter property make them good candidate for using them as sensors. Nevertheless, the growth of these materials under large scale remains difficult and chemical synthesis of these materials is highly desirable. Chemical colloidal synthesis of nanocrystals with non 0D dimensionality became possible only recently [1]. Colloidal nanocrystals are meanwhile of utmost interest because of their tunable optical properties from UV to infrared and even THz [2]. Recent progresses in colloidal synthesis made the synthesis of 2D anisotropic objects possible. In particular, cadmium chalcogenides compounds can be obtained with atomic scale control. The total absence of roughness on these objects leads to exceptional control of the optical properties with a total lack of inhomogeneous broadening (i.e. the ensemble luminescence signal is the same as the single particle spectrum). The obtained nanoparticles have a nanoplatelets shape (NPL). Their tunable thickness from 1 to 5 nm drives the optical properti
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