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Continuous advancements in science and technology in the field of flexible devices encourage researchers to dedicate themselves to seeking candidates for new flexible transparent conductive films (FTCFs). Our recently developed two-dimensional (2D) metal aerogels are considered as a new class of FTCFs. Here, we describe a new large-scale self-assembly synthesis of bimetallic Pt-Ni 2D metal aerogels with controllable morphology during the synthesis. The obtained 2D aerogels require only a low quantity of precursors for the synthesis of percolating nanoscale networks with areas of up to 6 cm2 without the need of an additional drying step. Stacks of the obtained monolayer structures display low sheet resistances (down to 270 Ω/sq), while decreasing the optical transparency. In perspective, the 2D bimetallic Pt-Ni aerogels not only enrich the structural diversity of metal aerogels but also bring forth new materials for further applications in flexible electronics and electrocatalysis with reduced costs of production.

We report a synthesis route to two-dimensional PbSe, HgSe, ZnSe, SnSe, and Cu-Zn-Sn-Se (CZTSe) nanomaterials based on cation exchange (CE) reactions. This approach includes two steps: it starts with the synthesis of hexagonal, up to several micrometers large yet approx. 5 nm-thick CuSe nanosheets (NSs), followed by CE of the host copper ions with the desired guest cation (Pb2+, Hg2+, Zn2+, or Sn4+). In the case of CZTSe, both guest cations can be added simultaneously since the variation of the guest cation ratio and reaction time can lead to various compositions. Mild reaction conditions allow for a preservation of the size and the 2D shape of the parent NSs accompanied by corresponding changes in their crystal structure. We furthermore demonstrate that the crystal structure of CuSe NSs can be rearranged even without addition of guest cations in the presence of tri-n-octylphosphine. Thus, the obtained NSs were further subjected to ligand exchange reactions in order to replace insulating bulky organic molecules on their surface with compact iodide and sulfide ions, a step crucial for the application of nanomaterials in (opto)electronic devices. The resulting NS dispersions were processed into thin films by spray-coating onto commercially available interdigitated platinum electrodes. Light response measurements of PbSe and CZTSe NS-films demonstrated their potential for applications as light-sensitive materials in photodetection or photovoltaics.

Cation exchange emerged as a versatile tool to obtain a variety of nanocrystals not yet available via a direct synthesis. Reduced reaction times and moderate temperatures make the method compatible with anisotropic nanoplatelets (NPLs). However, the subtle thermodynamic and kinetic factors governing the exchange require careful control over the reaction parameters to prevent unwanted restructuring. Here, we capitalize on the research success of CdSe NPLs by transforming them into PbSe NPLs suitable for optoelectronic applications. In a two-phase mixture of hexane/Nmethylformamide, the oleate-capped CdSe NPLs simultaneously undergo a ligand exchange to NH4I and a cation exchange reaction to PbSe. Their morphology and crystal structure are well-preserved as evidenced by electron microscopy and powder X-ray diffraction. We demonstrate the successful ligand exchange and associated electronic coupling of individual NPLs by fabricating a simple photodetector via spray-coating on a commercial substrate. Its optoelectronic characterization reveals a fast light response at low operational voltages.

In this work, we present a new synthetic approach to colloidal PbS nanoplatelets (NPLs) utilizing a cation exchange (CE) strategy starting from CuS NPLs synthesized via the hot-injection method. Whereas the thickness of the resulting CuS NPLs was fixed at approx. 5 nm, the lateral size could be tuned by varying the reaction conditions, such as time from 6 to 16 h, the reaction temperature (120 °C, 140 °C), and the amount of copper precursor. In a second step, Cu+ cations were replaced with Pb2+ ions within the crystal lattice via CE. While the shape and the size of parental CuS platelets were preserved, the crystal structure was rearranged from hexagonal covellite to PbS galena, accompanied by the fragmentation of the monocrystalline phase into polycrystalline one. Afterwards a halide mediated ligand exchange (LE) was carried out in order to remove insulating oleic acid residues from the PbS NPL surface and to form stable dispersions in polar organic solvents enabling thin-film fabrication. Both CE and LE processes were monitored by several characterization techniques. Furthermore, we measured the electrical conductivity of the resulting PbS NPL-based films before and after LE and compared the processing in ambient to inert atmosphere. Finally, we fabricated field-effect transistors with an on/off ratio of up to 60 and linear charge carrier mobility for holes of 0.02 cm2 V−1 s−1.