Halide Perovskites: Low Dimensions for Devices

Celebrating 10 years from the technological revolution brought about by the first report of halide perovskite solar cells, Symposium G of the EMRS Spring Meeting 2019 was dedicated to the memory of the late George C. Papavassiliou (Figure 1), a vibrant pioneer in the early days of the field during the 1990s. The Symposium, entitled "Halide Perovskites: low dimensions for devices", to reflect the important potential of these tunable semiconductors in technology, was designed with the intention of bringing together researchers from across all breadths and lengths of the field. From the discovery of new materials to the study of their photophysical properties-from both theory and experiment viewpoints-to more technical studies related to the implementation of perovskites into functional devices, the Symposium highlighted most aspects of the perovskite research that have been actively studied to date. In this respect, the symposium proved successful in providing key opportunities for discussions on progress in new material development as well as to introduce new potential applications beyond optoelectronics, with energy-related developments standing out. Among the 12 invited talks the 56 oral presentations and its 38 poster presentations (including a joint session with Symposium B-Emerging photovoltaics: strategies for more stable devices), the Symposium delivered lively discussion stimulated by the invited researchers who delineated the different themes of the Symposium. B. Lounis showed how the exciton-phonon coupling operates in perovskites, presenting an excellent account on the photo-physics of halide perovskite nanocrystals at the single-particle level 1. On a more applied topic, M. Bodnarchuk explained the intricacies of the synthesis and emission tuning of colloidal perovskite nanocrystals, showing how much the interface interactions between the inorganic perovskite and the organic surfactants can influence the properties, and proposed innovative methodologies on how to control the interactions 2. On the "phonon problem", R. Schaller presented a "high-throughput" study of many perovskite derivatives, experimentally pinpointing the anharmonic nature of the phonons that derive from the dynamically disordered nature of the crystal lattice 3. P. Plochocka covered the excitons present in the perovskites and highlighted very vividly how to manipulate excitons using (enormous) magnetic fields and extract useful information on their binding energy and lifetimes within the perovskite structure 4. Shifting the dimensionality to perovskite nanowires, the presentation of E. Horvath introduced many innovative methods to produce functional perovskite nanowires that can be shaped "at will" to various morphologies, by manipulating the substrate pattern and the surface conditions 5. Figure I.