Gary Hodes

Bio: Gary Hodes is an academic researcher from Weizmann Institute of Science. The author has contributed to research in topics: Perovskite (structure) & Photoelectrochemical cell. The author has an hindex of 77, co-authored 299 publications receiving 26253 citations. Previous affiliations of Gary Hodes include Centre national de la recherche scientifique & Jerusalem College of Engineering, Chennai.

Polyhedral and cylindrical structures of tungsten disulphide

Abstract: FOLLOWING the discovery of C60(ref. 1) and the advent of fullerene chemistry, considerable attention has been directed towards the associated cylindrical2,3 and polyhedral4,5 forms of graphite. To date, however, observations of such closed structures have been limited to the carbon system. Here we report the formation of equivalent stable structures in the layered semiconductor tungsten disulphide. After the heating of thin tungsten films in an atmosphere of hydrogen sulphide, transmission electron microscopy reveals a variety of concentric polyhedral and cylindrical structures (ranging in size from 100 nm) growing from the amorphous tungsten matrix. The closed nature of the structures is verified by electron diffraction and lattice imaging. As with the carbon system, complete closure of the tungsten disulphide layers requires the presence of structural defects (for example, edge dislocations), or the arrangement of atoms in polyhedra other than a planar hexagonal geometry.

Hybrid organic—inorganic perovskites: low-cost semiconductors with intriguing charge-transport properties

Abstract: Solution-processed hybrid organic–inorganic perovskites (HOIPs) exhibit long electronic carrier diffusion lengths, high optical absorption coefficients and impressive photovoltaic device performance. Recent results allow us to compare and contrast HOIP charge-transport characteristics to those of III–V semiconductors — benchmarks of photovoltaic (and light-emitting and laser diode) performance. In this Review, we summarize what is known and unknown about charge transport in HOIPs, with particular emphasis on their advantages as photovoltaic materials. Experimental and theoretical findings are integrated into one narrative, in which we highlight the fundamental questions that need to be addressed regarding the charge-transport properties of these materials and suggest future research directions. The charge transport properties of hybrid organic—inorganic perovskites, which can explain their excellent photovoltaic performance, are reviewed through an integrated summary of experimental and theoretical findings. The potential origins of these properties are discussed and future research directions are indicated.

How Important Is the Organic Part of Lead Halide Perovskite Photovoltaic Cells? Efficient CsPbBr3 Cells.

Abstract: Hybrid organic–inorganic lead halide perovskite photovoltaic cells have already surpassed 20% conversion efficiency in the few years that they have been seriously studied. However, many fundamental questions still remain unanswered as to why they are so good. One of these is “Is the organic cation really necessary to obtain high quality cells?” In this study, we show that an all-inorganic version of the lead bromide perovskite material works equally well as the organic one, in particular generating the high open circuit voltages that are an important feature of these cells.

Cesium Enhances Long-Term Stability of Lead Bromide Perovskite-Based Solar Cells.

Abstract: Direct comparison between perovskite-structured hybrid organic–inorganic methylammonium lead bromide (MAPbBr3) and all-inorganic cesium lead bromide (CsPbBr3), allows identifying possible fundamental differences in their structural, thermal and electronic characteristics. Both materials possess a similar direct optical band gap, but CsPbBr3 demonstrates a higher thermal stability than MAPbBr3. In order to compare device properties, we fabricated solar cells, with similarly synthesized MAPbBr3 or CsPbBr3, over mesoporous titania scaffolds. Both cell types demonstrated comparable photovoltaic performances under AM1.5 illumination, reaching power conversion efficiencies of ∼6% with a poly aryl amine-based derivative as hole transport material. Further analysis shows that Cs-based devices are as efficient as, and more stable than methylammonium-based ones, after aging (storing the cells for 2 weeks in a dry (relative humidity 15–20%) air atmosphere in the dark) for 2 weeks, under constant illumination (at max...

Perovskite-Based Solar Cells

Abstract: Photovoltaic (PV) cells that convert sunlight directly into electricity are becoming increasingly important in the world's renewable energy mix. The cumulative world PV installations reached around 100 GWp (gigawatts) ( 1 ) by the end of 2012. Some 85% use crystalline Si, with the rest being polycrystalline thin film cells, mostly cadmium telluride/cadmium sulfide ones. Thin-film cells tend to be cheaper to make with a shorter energy payback time. However, they do have the disadvantage, one that may become crucial when considering the terawatt range, that most of them contain rare elements like tellurium (as rare as gold), indium, and gallium. A newcomer to the PV field ( 2 ) has rapidly reached conversion efficiencies of more than 15% (see the figure). Based on organic-inorganic perovskite-structured semiconductors, the most common of which is the triiodide (CH3NH3PbI3), these perovskites tend to have high charge-carrier mobilities ( 3 , 4 ). High mobility is important because, together with high charge carrier lifetimes, it means that the light-generated electrons and holes can move large enough distances to be extracted as current, instead of losing their energy as heat within the cell. On pages 344 and 341 of this issue, Xing et al. ( 5 ) and Stranks et al. ( 6 ) use time-resolved transient absorption and photoluminescence to show that the effective diffusion lengths are indeed relatively large in CH3NH3PbI3, about 100 nm for both electrons and holes—a high value for a semiconductor formed from solution at low temperature.

A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films

Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.

Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells

Abstract: Two organolead halide perovskite nanocrystals, CH3NH3PbBr3 and CH3NH3PbI3, were found to efficiently sensitize TiO2 for visible-light conversion in photoelectrochemical cells. When self-assembled on mesoporous TiO2 films, the nanocrystalline perovskites exhibit strong band-gap absorptions as semiconductors. The CH3NH3PbI3-based photocell with spectral sensitivity of up to 800 nm yielded a solar energy conversion efficiency of 3.8%. The CH3NH3PbBr3-based cell showed a high photovoltage of 0.96 V with an external quantum conversion efficiency of 65%.

Two-dimensional atomic crystals

Abstract: We report free-standing atomic crystals that are strictly 2D and can be viewed as individual atomic planes pulled out of bulk crystals or as unrolled single-wall nanotubes. By using micromechanical cleavage, we have prepared and studied a variety of 2D crystals including single layers of boron nitride, graphite, several dichalcogenides, and complex oxides. These atomically thin sheets (essentially gigantic 2D molecules unprotected from the immediate environment) are stable under ambient conditions, exhibit high crystal quality, and are continuous on a macroscopic scale.

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites

Abstract: The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.