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

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 (recently employed in UV photodetection) make 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 is 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 intrabandgap electronic states. In this article we study all the steps to obtain phase pure [AgSePh]∞ NC films, from thin silver films deposition through its oxidation followed by a chemical vapor-solid reaction with benzeneselenol, by means of UV-vis, XRD, SEM, and AFM. Raman and FTIR spectroscopies 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 a 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 the precursor's leftovers or oxidized species that could contribute to the intragap states. By tuning the reaction parameters, we gained control of film morphology to obtain substrate-parallel oriented microcrystals showing different excitonic absorption intensities. Finally, centimeter-size high-quality [AgSePh]∞ NC films could be obtained, enabling exploitation of their optoelectronic properties, such as UV photodetection, in large-area applications.