Selective Silver Nanocluster Metallization on Conjugated Diblock Copolymer Templates for Sensing and Photovoltaic Applications

Abstract

Polymer−metal composite films with nanostructured metal and/or polymer interfaces show a significant perspective for optoelectronic applications, for example, as sensors or in organic photovoltaics (OPVs). The polymer components used in these devices are mostly nanostructured conductive polymers with conjugated π-electron systems. Enhanced OPV's power conversion efficiencies or sensor sensitivity can be achieved by selective metal deposition on or into polymer templates. In this study, we exploit time-resolved grazing-incidence X-ray scattering to observe the metal−polymer interface formation and the cluster crystallite size in situ during silver (Ag) sputter deposition on a poly(3-hexylthiophene-2,5-diyl)-b-poly(methyl methacrylate) (PMMA-b-P3HT) template. We compare the arising nanoscale morphologies with electronic properties, determine Ag growth regimes, and quantify the selective Ag growth for the diblock copolymer (DBC) template using the corresponding homopolymer thin films (P3HT and PMMA) as a reference. Hence, we are able to describe the influence of the respective polymer blocks and substrate effects on the Ag cluster percolation: the percolation threshold is correlated with the insulator-to-metal transition measured in situ with resistance measurements during the sputter deposition. The Ag cluster percolation on PMMA-b-P3HT starts already on the network of the hexagonal P3HT domain before a complete metal film covers the polymer surface, which is complemented by microscopic measurements. In general, this study demonstrates a possible method for the selective Ag growth as a scaffold for electrode preparation in nanoelectronics and for energy harvesting applications.

Correlating Optical Reflectance with the Topology of Aluminum Nanocluster Layers Growing on Partially Conjugated Diblock Copolymer Templates

“…Larger Al thicknesses are shown in Figure S2 in the Supporting Information. A different growth of Al on PMMA- b -P3HT is seen compared to Ag on the DBC template, which formed cylindrically shaped Ag clusters on the P3HT domain of the DBC . At the early stages of the Al sputter deposition (δ Al < 1 nm), Al forms small clusters on the P3HT domain, which connect very fast to wormlike Al nanostructures growing in their size (Figure e), comparable to earlier results …”

“…The majority of Al clusters are more uniformly distributed and form a nanogranular layer on top of the Al wormlike nanostructures, which induces the higher plasmonic activity around δ Al = 2 nm. We observe a reduced number of well-separated Al clusters compared to the early stages of Ag growth on P3HT homopolymer thin films, while Ag directly forms a nanogranular layer until δ Al = 4 nm . The wormlike Al growth on the PMMA- b -P3HT template is ongoing until around δ Al = 2 nm (as seen in Figure d).…”

“…The selective wetting of Al on the P3HT block is observed up to an Al thickness of δ Al = 5 nm, and its self-assembly into Al nanostructures is quantified by GISAXS, atomic force microscopy (AFM), UV–vis spectroscopy, and field emission scanning electron microscopy (FESEM). The wetting of Al on the PMMA- b -P3HT DBC film shows pronounced growth differences in cluster size, shape, and formation compared to previous studies with Ag on this DBC template . The direct correlation of morphological, chemical, and optical properties of the Al formation on the DBC gives insight into the early Al–polymer chemical interaction and allows for understanding the formation for large-scale fabrication of optical sensors and electrode materials for organic solar cells.…”

“…Afterward, the substrates were cleaned with ultraclean water, dried with nitrogen, and spin-coated (6-RC, SÜSS Micro Tec Lithography, Germany; rpm 3000, ramp 1, time 30 s) with the three different polymer solutions. The concentrations (5 mg/mL) of the polymer solutions for the three different polymer thin films were optimized to have a film thickness δ = (20 ± 3) nm …”

“…In previous studies, we investigated the interaction of Ag with polystyrene (PS), poly­(methyl methacrylate) (PMMA), and poly­(3-hexylthiophen-2,5-diyl) (P3HT) polymer surfaces using surface-sensitive methods such as GISAXS and XPS to reveal the topological changes and chemical interactions. , The chemical interaction of noble metals such as Ag was proven with several molecular components, e.g ., oxygen and sulfur. Ag was reacting with different molecular components of the polymer template as, for example, PS, PMMA, and P3HT, which lead to a different cluster growth depending on the specific interaction .…”