Understanding the Synthetic Pathway to Large-Area, High-Quality [AgSePh]_∞ Nanocrystal Films

Abstract

Silver benzeneselenolate [AgSePh]∞ is a coordination polymer that hosts a hybrid quantum well structure. The recent advancements in the study of its tightly bound excitons (~300 meV) and photoconductive properties makes it an interesting representative of a material platform that is an environmentally stable alternative to 2D metal halide perovskites in terms of optoelectronic properties. To this aim, several challenges are to be addressed, among which the lack of control over the metal-organic reaction process in the reported synthesis of the [AgSePh]∞ nanocrystal film (NC). This issue contributed to cast doubts over the origin of its intra-bandgap electronic states. In this article we study all the steps to obtain phase pure [AgSePh]∞ NC films, from thin silver films through its oxidation and reaction via a chemical vapor-solid with benzeneselenol, by means of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopy are also employed to provide vibrational peaks assignment, for the first time on this polymer. Our analysis supports an acid-base reaction scheme based on an acid attacking the metal oxide precursor, generating water as byproduct of the polymeric synthesis, speeding up the reaction by solvating the PhSeH. The reaction readily goes to completion within 30 min in a supersaturated PhSeH / N2 atmosphere at 90 °C. Our analysis suggests the absence of precursor's leftovers or oxidized species that could contribute to the intra-gap states. By tuning the reaction parameters, we gained control on film morphology to obtain substrate-parallel oriented micro-crystals showing different excitonic absorption intensities. Finally, centimeters size high quality [AgSePh]∞ NC films could be obtained, enabling exploitation of their optoelectronic properties, such as UV photodetection, in largearea applications.

Size and Quality Enhancement of 2D Semiconducting Metal–Organic Chalcogenolates by Amine Addition

“…Of the 2D MOCs reported so far, silver phenyl­selenolate (AgSePh) ,− has received the most attention because of its blue luminescence (Figure a) and in-plane anisotropy, which are attractive features for light-emitting applications and light–matter coupling. AgSePh naturally adopts a multi-quantum-well structure consisting of slabs of silver selenide separated by layers of phenyl rings (Figure b), leading to a high exciton binding energy of ∼400 meV , and a picosecond photoluminescence (PL) lifetime .…”

“…24 Furthermore, AgSePh can be prepared in different forms, depending on the end use need. For example, AgSePh thin films can be prepared by a scalable vapor-phase chemical transformation, 21,25 and microcrystals can be synthesized by a solution-phase hydrothermal synthesis. 22 However, these methods typically yield small AgSePh crystals with average lateral sizes of <5 μm, making fundamental studies and device integration challenging.…”

Morphological Control of 2D Hybrid Organic–Inorganic Semiconductor AgSePh

“…Metal–organic chalcogenolates (MOCs) of coinage metals are nontoxic covalently bound hybrid organic–inorganic materials with [M­(ER)] n chemical formula, where M = Cu­(I), Ag­(I), Au­(I); E = S, Se, Te; and R is an organic hydrocarbon . Recently, silver phenylselenolate (AgSePh), a 2D member of the broader class of MOC coordination polymers, has gained a renewed interest as a class of hybrid organic–inorganic 2D semiconductors (Figure a). − While AgSePh was discovered and its structure refined almost 20 years ago, its semiconducting properties were not realized until 2018. , Recent studies − have demonstrated many promising properties of AgSePh such as strong exciton binding energy, , chemical robustness, , nontoxic elemental composition, in-plane anisotropy, and low-cost and scalable synthetic methods. , Moreover, the covalent interaction between organic and inorganic layers potentially provides an opportunity to control the properties of 2D semiconductors through organic functionalization as shown in the thiolate analogues of AgSePh …”

Light Emission in 2D Silver Phenylchalcogenolates

“…Among the 2D MOCs reported so far, silver phenylselenolate (AgSePh), also known as “mithrene”, has attracted the most attention due to its natural blue (∼467 nm) emission. ,− It was shown that silver phenyltellurolate (AgTePh), known as “tethrene”, also crystallizes into a 2D structure at room temperature with the same monoclinic centrosymmetric space group C 2/ c as AgSePh. , (Note that AgSePh has also been reported in the P 2 1 / c structure, which is very similar in structure to C 2/ c .) However, AgTePh exhibits a strikingly different optical behavior from AgSePh despite the structural and compositional similarity, implying a different physical mechanism underlying light emission in AgTePh.…”