success of epitaxial growth of conventional inorganic semiconductors for (opto) electronics, there are various attempts to obtain single-crystalline structures by the epitaxial growth of metal halide perovskites (MHPs), as promising materials for optoelectronic applications. While most attempts have been pursued by some ways of chemical vapor deposition (CVD) on various substrates and also by molecular beam epitaxy, [1][2][3][4][5][6][7][8] albeit with elaborate equipment, the advantages of the MHPs are enrolled by solution processing them. Solution epitaxy is an inexpensive and facile approach to obtain high-quality films and microstructures. Simple techniques such as spin coating delivered already epitaxial crystalline films operating as highly sensitive photodetectors. [9] Thereafter, spin coating was introduced by Kelso et al., as a general technique for the epitaxial growth of inorganic High-quality epitaxial growth of oriented microcrystallites on a semiconductor substrate is demonstrated here for formamidinium lead bromide perovskite, by drop casting of precursor solutions in air. The microcrystallites exhibit green photoluminescence at room temperature, as well as lasing with low thresholds. Lasing is observed even though the substrate is fully opaque at the lasing wavelengths, and even though it has a higher refractive index as the perovskite active material. Moreover, the lasing is stable for more than 10 9 excitation pulses, which is more than what is previously achieved for devices kept in the air. Such highly stable lasing under pulsed excitation represents an important step towards continuous mode operation or even electrical excitation in future perovskite-based devices.

Epitaxial growth methods usually need dedicated equipment, high energy consumption to maintain pure vacuum conditions and evaporation of source materials, and elevated substrate temperatures. Solution epitaxial growth requires nothing of that but is rarely used because the achieved microstructures are of low quality, not homogeneous, and finally exhibit worse performances in devices. Here, an antisolvent‐vapor‐assisted‐crystallization of metal‐halide‐perovskites as a method overcoming these disadvantages is demonstrated. The methylammonium lead tribromide exhibits van‐der‐Waals type of epitaxial growth on mica substrates, resulting in micro‐crystallites whose shape can be controlled to be either triangular micro‐prism or micro‐cuboid. These micro‐crystallites act as optical resonators supporting various optical modes and lasing is achieved under optical excitation with low thresholds and record high environmental stability. Selecting suitable resonators from a large variety of sizes allows control of mode spacing and finally mono‐mode operation, considered to be an important feature of semiconductor laser devices. The achieved results are essentially competitive to those obtained by vapor phase epitaxial microstructures, highlighting that epitaxy of high‐quality optoelectronic device structures is feasible by minimum technological efforts and energy consumption, which are of increasing importance considering issues such as global warming and the current energy crisis.

Aliovalent-doped metal oxide nanocrystals exhibiting localized surface plasmons (LSPRs) are applied in systems that require reflection/scattering/absorption in infrared and optical transparency in visible. Indium tin oxide (ITO) is currently leading the field, but indium resources are known to be very restricted. Antimony-doped tin oxide (ATO) is a cheap candidate to substitute the ITO, but it exhibits less advantageous electronic properties and limited control of the LSPRs. To date, LSPR tuning in ATO NCs has been achieved electrochemically and by aliovalent doping, with a significant decrease in doping efficiency with an increasing doping level. Here, we synthesize plasmonic ATO nanocrystals (NCs) via a solvothermal route and demonstrate ligand exchange to tune the LSPR energies. Attachment of ligands acting as Lewis acids and bases results in LSPR peak shifts with a doping efficiency overcoming those by aliovalent doping. Thus, this strategy is of potential interest for plasmon implementations, which are of potential interest for infrared upconversion, smart glazing, heat absorbers, or thermal barriers.