Excitonic Behavior and Photo-Carriers Transport in 2D Quantum Confined Metal Organic Chalcogenides

Two-dimensional (2D) excitons arise from electron-hole confinement along one spatial dimension. Such excitations are often described in terms of Frenkel or Wannier models according to the degree of exciton spatial localization and the surrounding dielectric environment. In hybrid material systems, such as the 2D perovskites, the two models break down at the intermediate regime where a different physical description is needed. We significantly enrich this framework of studies by considering a tunable airstable material platform where covalently bonded metalchalcogenide layers are spaced by organic ligands that provide confinement barriers for charge carriers in the inorganic layer. As representative of the material class, we consider self-assembled,layered bulk silver benzeneselenolate, [AgSePh]∞. We show that in this non-polar dielectric environment, strongly anisotropic excitons dominate the optical transitions. We then investigate the charge carriers’ transport, critical aspect for most optoelectronic devices, in a [AgSePh]∞ nanocrystal (NC) film. UV photoemission spectroscopy is used to extract the valence band energy edge and suitable metal contacts were fabricated to inject charge carriers. By temperature-dependent electrical measurements the activation energy for dark charge transport was in was determined to be 1.10eV. Photo-generated carriers could be extracted and the wavelength-dependent photo-response of the NC film suggest possible use of this materials as UV photodetector. We therefore built a planar photo-detector and characterized it in terms of sensitivity and frequency-dependent response. Finally, given the versatility of the [AgSePh]∞ NC film we validated its reliability as air-stable UV detector on flexible substrates.