日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

State of the Art and Prospects for Halide Perovskite Nanocrystals.

The performance of organometallic perovskite solar cells has rapidly surpassed those of both traditional dye-sensitized and organic photovoltaics, e.g. solar cells based on CH3NH3PbI3 have recently reached 18% conversion efficiency. We analyze its electronic structure and optical properties within the quasiparticle self-consistent GW approximation (QSGW ). Quasiparticle self-consistency is essential for an accurate description of the band structure: bandgaps are much larger than what is predicted by the local density approximation (LDA) or GW based on the LDA. Several characteristics combine to make the electronic structure of this material unusual. First, there is a strong driving force for ferroelectricity, as a consequence the polar organic moiety CH3NH3. The moiety is only weakly coupled to the PbI3 cage; thus it can rotate give rise to ferroelectric domains. This in turn will result in internal junctions that may aid separation of photoexcited electron and hole pairs, and may contribute to the current-voltage hysteresis found in perovskite solar cells. Second, spin orbit modifies both valence band and conduction band dispersions in a very unusual manner: both get split at the R point into two extrema nearby. This can be interpreted in terms of a large Dresselhaus term, which vanishes at R but for small excursions about R varies linearly in k. Conduction bands (Pb 6p character) and valence bands (I 5p) are affected differently; moreover the splittings vary with the orientation of the moiety. We will show how the splittings, and their dependence on the orientation of the moiety through the ferroelectric effect, have important consequences for both electronic transport and the optical properties of this material.

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-020499.pdf

Electronic structure of hybrid halide perovskite photovoltaic absorbers

Based on electronic structure and atomic size considerations, nitrogen has been regarded as the most suitable impurity for p-type doping in ZnO. However, numerous experimental efforts by many different groups have not resulted in stable and reproducible p-type material, casting doubt on the efficacy of nitrogen as a shallow acceptor. Based on advanced first-principles calculations we find that nitrogen is actually a deep acceptor, with an exceedingly high ionization energy of 1.3 eV, and hence cannot lead to hole conductivity in ZnO. In light of this result, we reexamine prior experiments on nitrogen doping of ZnO.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-001476.pdf

Why nitrogen cannot lead to p-type conductivity in ZnO

Lead-free double perovskite materials, A2M(I)M′(III)X6, have recently attracted attention as environment-friendly alternatives to lead-based perovskites, APbX3, because of both rich fundamental sci...

Band Gap Engineering in Cs2(NaxAg1-x)BiCl6 Double Perovskite Nanocrystals.

Lead-free halide double perovskites (DPs) have emerged as a stable and greener alternative to very toxic lead-based perovskites owing to their outstanding photophysical properties. Here, a series o...

Lead-Free Alloyed Double-Perovskite Nanocrystals of Cs2(NaxAg1–x)BiBr6 with Tunable Band Gap

The electrocatalytic water splitting activity of layered transition metal dichalcogenides (TMDs) is limited by inert basal planes and slower reaction kinetics. Here, we demonstrate the use of MoSe2–Cu2S nanoheterostructures (NHSs) as an efficient electrocatalyst for water splitting. The interfacial engineering of the basal planes of MoSe2 nanosheets (NSs) with Cu2S nanocrystals (NCs) increases the number of active sites for oxygen evolution reaction (OER), owing to the decoration of inert basal planes of MoSe2 NSs with an OER active material i.e. Cu2S NCs. Density functional theory calculations revealed a favorable type-II band alignment, and built-in electric field at heterointerfaces, significantly decreasing the energy barrier for interfacial charge transfer. As a consequence of the simultaneous increase of number of active sites and modulation of the electronic structure, the MoSe2–Cu2S NHSs exhibit higher OER activity with an overpotential of 264 mV at 10 mA cm−2 current density. The built-in electric field phenomenon also greatly promotes hydrogen evolution reaction (HER) activity of MoSe2–Cu2S NHSs in alkaline medium on account of the decreased kinetic energy barrier. This study sheds light on the importance of designing NHS-derived systems to tune the electrocatalytic properties for water splitting.

Understanding the efficient electrocatalytic activities of MoSe2–Cu2S nanoheterostructures

Mixed-dimensional van der Waals nanohybrids (MvNHs) of two-dimensional transition-metal dichalcogenides (TMDs) and zero-dimensional perovskites are highly promising candidates for high-performance photonic device applications. However, the growth of perovskites over the surface of TMDs has been a challenging task due to the distinguishable surface chemistry of these two different classes of materials. Here, we demonstrate a synthetic route for the design of MoSe2-CsPbBr3 MvNHs using a bifunctional ligand, i.e., 4-aminothiophenol. Close contact between these two materials is established via a bridge that leads to the formation of a donor-bridge-acceptor system. The presence of the small conjugated ligand facilitates faster charge diffusion across MoSe2-CsPbBr3 interfaces. Density functional theory calculations confirm the type-II band alignment of the constituents within the MvNHs. The MoSe2-CsPbBr3 nanohybrids show much higher photocurrent (∼2 × 104-fold photo-to-dark current ratio) as compared to both pure CsPbBr3 nanocrystals and pristine MoSe2 nanosheets owing to the synergistic effect of pronounced light-matter interactions followed by efficient charge separation and transportation. This study suggests the use of a bifunctional ligand to construct a nanohybrid system to tune the optoelectronic properties for potential applications in photovoltaic devices.

Enhanced Photocurrent Owing to Shuttling of Charge Carriers across 4-Aminothiophenol-Functionalized MoSe2–CsPbBr3 Nanohybrids

TiO2 anatase is considered to play a significant importance in energy and environmental research. However, for developing artificial photosynthesis with TiO2, the major drawback is its large bandgap of 3.2 eV. Several non-metals have been used experimentally for extending the TiO2 photo-absorption to the visible region of the spectrum. It’s therefore of paramount importance to provide theoretical guidance to experiment about the kind of defects that are thermodynamically stable at a realistic condition (e.g. Temperature (T), oxygen partial pressure (
 $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$
 ), doping). However, disentangling the relative stability of different types of defects (viz. substitution, interstitial, etc.) as a function of charge state and realistic T, $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$
 is quite challenging. We report here using state-of-the-art first-principles based methodologies, the stability and meta-stability of different non-metal dopants X (X = N, C, S, Se) at various charge states and realistic conditions. The ground state electronic structure is very accurately calculated via density functional theory with hybrid functionals, whereas the finite T and $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$
 effects are captured by ab initio atomistic thermodynamics under harmonic approximations. On comparing the defect formation energies at a given T and $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$
 (relevant to the experiment), we have found that Se interstitial defect (with two hole trapped) is energetically most favored in the p-type region, whereas N substitution (with one electron trapped) is the most abundant defect in the n-type region to provide visible region photo-absorption in TiO2. Our finding validates that the most stable defects in X doped TiO2 are not the neutral defects but the charged defects. The extra stability of $${({\bf{S}}{\bf{e}}{\bf{O}})}_{{\bf{O}}}^{+{\bf{2}}}$$
 is carefully analyzed by comparing the individual effect of bond-making/breaking and the charge carrier trapping energies.

/pdf/stability-of-non-metal-dopants-to-tune-the-photo-absorption-i8ztirrcxj.pdf

Pooja Basera

Papers

Band Gap Engineering in Cs2(NaxAg1-x)BiCl6 Double Perovskite Nanocrystals.

Lead-Free Alloyed Double-Perovskite Nanocrystals of Cs2(NaxAg1–x)BiBr6 with Tunable Band Gap

Understanding the efficient electrocatalytic activities of MoSe2–Cu2S nanoheterostructures

Enhanced Photocurrent Owing to Shuttling of Charge Carriers across 4-Aminothiophenol-Functionalized MoSe2–CsPbBr3 Nanohybrids

Stability of non-metal dopants to tune the photo-absorption of TiO 2 at realistic temperatures and oxygen partial pressures: A hybrid DFT study