Spotlights pubs.acs.org/JPCL
Spotlights: Volume 7, Issue 16
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RASHBA EFFECT AND CARRIER MOBILITY IN HYBRID ORGANIC−INORGANIC PEROVSKITES
RANGE, MAGNITUDE, AND ULTRAFAST DYNAMICS OF ELECTRIC FIELDS AT THE HYDRATED DNA SURFACE The electric properties of hydrated charged biointerfaces remain controversial, and Siebert et al. shed some light on the subject in their Letter (DOI: 10.1021/acs.jpclett.6b01369). The authors tested salmon testes DNA in its native hydration shell; by building the water shell layer by layer, they were able to trace fluctuating electric fields at the surface of the DNA via their interactions with backbone vibrations in a wide range of hydration levels. They identified water molecules within two solvent shells as the main source of interfacial electric fields, determined the subnanometer field range, and established the time scale and amplitudes of electric field fluctuations. Their findings extend existing knowledge of the electrical interaction of DNA with its immediate environment and provide a target for theory and simulation.
Hybrid organic−inorganic perovskites (HOIPs) perform very efficiently in photovoltaic applications, largely because of their carrier transport properties. Zhi-Gang Yu of Washington State University studied underlying mechanisms of the charge transport of these perovskites, and he found that the Rashba effect plays a part by enhancing acoustic-phonon scattering and altering the temperature dependence of carrier mobility. The Rashba effect produces a splitting of spin states owing to the interplay of spin−orbit coupling and asymmetry of a potential. Yu describes the role of the Rashba effect in the charge transport of HOIPs (DOI: 10.1021/acs.jpclett.6b01404). His findings could lead to a wider understanding of the special electronic properties of HOIPs.
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MOLECULAR RESOLUTION IN SITU IMAGING OF SPONTANEOUS GRAPHENE EXFOLIATION
MODERATE HUMIDITY DELAYS ELECTRON−HOLE RECOMBINATION IN HYBRID ORGANIC−INORGANIC PEROVSKITES: TIME-DOMAIN AB INITIO SIMULATIONS RATIONALIZE EXPERIMENTS It is known that humidity affects the performance of hybrid perovskite solar cells, but the effects can be positive or negative. The mechanism responsible for the increase or decrease of perovskite solar cell efficiency under humidity has remained largely unclear, and Long et al. address the problem (DOI: 10.1021/acs.jpclett.6b01412). Using simulations, the authors show how small numbers of water molecules tend to perturb the surface layer of perovskites, to localize the photoexcited electron close to the surface, and to avoid electron traps. This results in a decrease of the electron−hole overlap and a subsequent increase in the lifetime of the excited state. However, in large amounts, water molecules form stable hydrogen-bonded networks and have little effect on charge localization. At the same time, by contributing high-frequency polar vibrations, they increase nonadiabatic coupling and accelerate nonradiative energy losses, thus degrading performance. These findings rationalize the conflicting experimental results and advance our understanding of excited-state dynamics in perovskite solar cells.
Graphene has been called a miracle material because of its strength, flexibility, and myriad potential uses in nearly every area of our lives, from touchscreens to water purification to LEDs to efficient solar cells, but widespread commercialization has been hampered by the high cost of its production and the challenge of long-term storage. Spontaneous exfoliationi.e., without shaking, stirring, or sonicationis a promising solution to the problem. Elbourne et al. studied the spontaneous exfoliation of graphene into ionic liquids at room temperature and provide in situ images of the process. Their work, described in this Letter (DOI: 10.1021/acs.jpclett.6b01323), could lead to the discovery of other liquids and solutions that can facilitate truly spontaneous graphene exfoliation, thus enabling largescale production of graphene that can be stored indefinitely.
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THE MOLECULAR MECHANISM OF IRON(III) OXIDE NUCLEATION
Scheck et al. attempt to fill the significant gaps in the current knowledge of iron oxide nucleation and precipitationgaps caused in part by the difficulty in identifying the event of phase separation, especially with respect to the nucleation mechanism. In this Letter (DOI: 10.1021/acs.jpclett.6b01237), the authors find that nucleation is governed not by a critical size but rather by the dynamics of the clusters that are forming at the distinct nucleation stages, based on the chemistry of the linkages within the clusters. They report two key findings: (i) The nanoscopic, inorganic polymeric species that have been observed in numerous iron(III) oxide systems are thermodynamically stable solutes, thus meeting the requirements for classification as prenucleation clusters, not nuclei (as understood in classical nucleation theory); (ii) agglomeration is triggered by a reduction of prenucleation cluster dynamics based on a change in the reaction mechanism. © 2016 American Chemical Society
Published: August 18, 2016 3294
DOI: 10.1021/acs.jpclett.6b01782 J. Phys. Chem. Lett. 2016, 7, 3294−3294
