Showing papers by "Prashant V. Kamat published in 2014"

An inorganic hole conductor for organo-lead halide perovskite solar cells. Improved hole conductivity with copper iodide.

Abstract: Organo-lead halide perovskite solar cells have emerged as one of the most promising candidates for the next generation of solar cells. To date, these perovskite thin film solar cells have exclusively employed organic hole conducting polymers which are often expensive and have low hole mobility. In a quest to explore new inorganic hole conducting materials for these perovskite-based thin film photovoltaics, we have identified copper iodide as a possible alternative. Using copper iodide, we have succeeded in achieving a promising power conversion efficiency of 6.0% with excellent photocurrent stability. The open-circuit voltage, compared to the best spiro-OMeTAD devices, remains low and is attributed to higher recombination in CuI devices as determined by impedance spectroscopy. However, impedance spectroscopy revealed that CuI exhibits 2 orders of magnitude higher electrical conductivity than spiro-OMeTAD which allows for significantly higher fill factors. Reducing the recombination in these devices could ...

Band filling with free charge carriers in organometal halide perovskites

Abstract: Femtosecond transient absorption spectroscopy measurements indicate that the dominant relaxation pathway for excited states in perovskite materials is by recombination of free electrons and holes.

Recent Advances in Quantum Dot Surface Chemistry

Abstract: Quantum dot (QD) surface chemistry is an emerging field in semiconductor nanocrystal related research. Along with size manipulation, the careful control of QD surface chemistry allows modulation of the optical properties of a QD suspension. Even a single molecule bound to the surface can introduce new functionalities. Herein, we summarize the recent advances in QD surface chemistry and the resulting effects on optical and electronic properties. Specifically, this review addresses three main issues: (i) how surface chemistry affects the optical properties of QDs, (ii) how it influences the excited state dynamics, and (iii) how one can manipulate surface chemistry to control the interactions between QDs and metal oxides, metal nanoparticles, and in self-assembled QD monolayers.

Glutathione-Capped Gold Nanoclusters as Photosensitizers. Visible Light-Induced Hydrogen Generation in Neutral Water

Abstract: Glutathione-capped metal nanoclusters (Aux-GSH NCs) which exhibit molecular-like properties are employed as a photosensitizer for hydrogen generation in a photoelectrochemical cell (PEC) and a photocatalytic slurry reactor. The reversible reduction (E0 = −0.63 V vs RHE) and oxidation (E0 = 0.97 and 1.51 V vs RHE) potentials of these metal nanoclusters make them suitable for driving the water-splitting reaction. When a mesoscopic TiO2 film sensitized by Aux-GSH NCs is used as the photoanode with a Pt counter electrode in aqueous buffer solution (pH = 7), we observe significant photocurrent activity under visible light (400–500 nm) excitation. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs in an aqueous slurry system and irradiating with visible light produce H2 at a rate of 0.3 mmol of hydrogen/h/g of Aux-GSH NCs. The rate of H2 evolution is significantly enhanced (∼5 times) when a sacrificial donor, such as EDTA, is introduced into the system. Using metal nanoclusters as a photosensitize...

Size-Dependent Excited State Behavior of Glutathione-Capped Gold Clusters and Their Light-Harvesting Capacity

Abstract: Glutathione-protected gold clusters exhibit size-dependent excited state and electron transfer properties. Larger-size clusters (e.g., Au25GSH18) with core-metal atoms display rapid (<1 ps) as well as slower relaxation (∼200 ns) while homoleptic clusters (e.g., Au10–12GSH10–12) exhibit only slower relaxation. These decay components have been identified as metal–metal transition and ligand-to-metal charge transfer, respectively. The short lifetime relaxation component becomes less dominant as the size of the gold cluster decreases. The long-lived excited state and ability to participate in electron transfer are integral for these clusters to serve as light-harvesting antennae. A strong correlation between the ligand-to-metal charge-transfer excited state lifetime and photocatalytic activity was evidenced from the electron transfer to methyl viologen. The photoactivity of these metal clusters shows increasing photocatalytic reduction yield (0.05–0.14) with decreasing cluster size, Au25 < Au18 < Au15 < Au10–...

Switching the reaction course of electrochemical CO₂ reduction with ionic liquids.

Abstract: The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) offers new ways to modulate the electrochemical reduction of carbon dioxide. [emim][Tf2N], when present as the supporting electrolyte in acetonitrile, decreases the reduction overpotential at a Pb electrode by 0.18 V as compared to tetraethylammonium perchlorate as the supporting electrolyte. More interestingly, the ionic liquid shifts the reaction course during the electrochemical reduction of carbon dioxide by promoting the formation of carbon monoxide instead of oxalate anion. With increasing concentration of [emim][Tf2N], a carboxylate species with reduced CO2 covalently bonded to the imidazolium ring is formed along with carbon monoxide. The results highlight the catalytic effects of the medium in modulating the CO2 reduction products.

Size-Dependent Photovoltaic Performance of CuInS2 Quantum Dot-Sensitized Solar Cells

Abstract: The optical and electronic properties of quantum dots (QDs), which are drastically affected by their size, have a major impact on their performance in devices such as solar cells. We now report the size-dependent solar cell performance for CuInS2 QDs capped with 1-dodecanethiol. Pyramidal shaped CuInS2 QDs with diameters between 2.9 and 5.3 nm have been synthesized and assembled on mesoscopic TiO2 films by electrophoretic deposition. Time-resolved emission and transient absorption spectroscopy measurements have ascertained the role of internal and surface defects in determining the solar cell performance. An increase in power conversion efficiency (PCE) was observed with the increasing size of QDs, with maximum values of 2.14 and 2.51% for 3.9 and 4.3 nm size particles, respectively. The drop in PCE observed for larger QDs (5.3 nm) is attributed to decreased charge separation following bandgap excitation. Because the origin of photocurrent generation in CuInS2 QDSC arises from the defect-dominated charge ...

Best practices for reporting on heterogeneous photocatalysis.

Abstract: H photocatalysis is of broad interest in materials chemistry and materials science, particularly with the rapid growth of research attention being directed toward energy-related applications, pollution mitigation, and other related areas of environmental impact. A literature survey reveals more than 9000 papers with the word photocatalyst or photocatalysis in the title published during the last ten years (Source: Web of Science, July 3, 2014), with the number of papers published each year increasing significantly since 2005. The materials and physical chemistry journals of the American Chemical Society receive a significant number of papers in the area of photocatalysis. As editors of Chemistry of Materials, ACS Applied Materials & Interfaces, and The Journal of Physical Chemistry Letters, we have written this Editorial to draw the attention of authors, reviewers, and readers to the importance of uniform guidelines for the analysis and characterization of new and modified heterogeneous photocatalyst materials. These best practices for photocatalysis characterization and efficiency reporting are not new to the photocatalyst community; indeed, they have been repeatedly discussed within the research community over many years. Nonetheless, we as editors continue to receive papers for consideration that report on poorly characterized photocatalysts and make exaggerated claims, such as "highly efficient," "superior efficiency," or "improved efficiency," without properly disclosing the conditions and experimental procedures used to characterize the catalyst materials and determine the photocatalytic efficiencies. As a result, the major conclusions of the papers are oftentimes not supported by the experimental results, and comparisons with prior literature near impossible, which raises suspicions that the paper may be unreliable. These papers may suffer the consequence of poor review, or worse, being declined without external review. The challenge in attempting to provide a list of requirements for publication of a new or modified photocatalyst is that the diversity of materials is high, and thus delineating a one-sizefits-all template is not realistic. We hope, however, to outline the essentials that could serve as a starting point for any paper that describes photocatalytic performance. At a minimum, the following points should be addressed by each paper that discloses the performance of new or modified photocatalyst materials: Photocatalyst Characterization. New (nano)materials should be properly and fully characterized, including X-ray diffraction analysis, electron microscopy, X-ray photoelectron spectroscopy, effective surface area determination (BET measurements), light absorption characteristics (including diffuse reflectance spectroscopy, or if soluble or in thin-film form, UV−visible spectroscopy), and other techniques that may be relevant to the material(s) in question. If recording an emission spectrum, it is important to identify the origin of emission by taking an accompanying excitation spectrum. (Caution: Organic impurities often contribute to blue emission under UV excitation.) Reporting of Photocatalytic Efficiencies. The conditions under which the efficiency of a photocatalyst is determined must be carefully and thoroughly defined including the following: Catalyst loading (or area and thickness if a film), the source and wavelength of light used for illumination (if monochromatic), or the wavelength distribution of light (if broadband), the optical irradiance at the sample (mW cm−2) or total optical power impinging on the sample if liquid (mW mL−1), and the substrate concentration. Studies should also include measurement of the apparent quantum efficiency, defined as

Kinetics and mechanism of (•)OH mediated degradation of dimethyl phthalate in aqueous solution: experimental and theoretical studies.

Abstract: The hydroxyl radical (•OH) is one of the main oxidative species in aqueous phase advanced oxidation processes, and its initial reactions with organic pollutants are important to understand the transformation and fate of organics in water environments. Insights into the kinetics and mechanism of •OH mediated degradation of the model environmental endocrine disruptor, dimethyl phthalate (DMP), have been obtained using radiolysis experiments and computational methods. The bimolecular rate constant for the •OH reaction with DMP was determined to be (3.2 ± 0.1) × 109 M–1s–1. The possible reaction mechanisms of radical adduct formation (RAF), hydrogen atom transfer (HAT), and single electron transfer (SET) were considered. By comparing the experimental absorption spectra with the computational results, it was concluded that the RAF and HAT were the dominant reaction pathways, and OH-adducts (•DMPOH1, •DMPOH2) and methyl type radicals •DMP(-H)α were identified as dominated intermediates. Computational results co...

Excited-State Behavior of Luminescent Glutathione-Protected Gold Clusters

Abstract: The excited-state behavior of luminescent gold clusters provides new insights in understanding their photocatalytic activity in the visible region. The excited state of glutathione-protected gold nanoclusters (AuGSH), which is characterized by the long-lived excited state (τ = 780 ns), arises from the ligand-to-metal type transition. These AuGSH clusters are in a partially oxidized state (Au(I)) and are readily reduced by chemical or electrochemical methods. Interestingly, a metal core transition with short-lived lifetime (τ < 3 ps) appears along with a longer lifetime in reduced AuGSH clusters. The role of the oxidation state of gold clusters in dictating the photocatalytic reduction of methyl viologen is discussed.

Is Graphene a Stable Platform for Photocatalysis? Mineralization of Reduced Graphene Oxide With UV-Irradiated TiO2 Nanoparticles

Abstract: The recent thrust in utilizing reduced graphene oxide (RGO) as a support for nanostructured catalyst particles has led to the claims of improved efficiency in solar cells, fuel cells, and photocatalytic degradation of pollutants. Specifically, the robust TiO2 system is often coupled with RGO to improve charge separation and facilitate redox reactions. Here, we probe the stability of RGO in the presence of UV-excited TiO2 in aqueous media and establish its reactivity toward OH• radicals, a primary oxidant generated at the TiO2 surface. By probing changes in absorption, morphology, and total organic carbon content (TOC), we conclusively demonstrate the vulnerability of RGO toward OH• attack and raise the concern of its use in many applications where OH• are likely to be formed. On the other hand, the OH• radical-mediated mineralization could also enable new approaches in tackling environmental remediation of nanocarbons such as RGO, carbon nanotubes, and fullerenes.

Quantum dot solar cells: Hole transfer as a limiting factor in boosting the photoconversion efficiency

Abstract: Semiconductor nanostructures are attractive for designing low-cost solar cells with tunable photoresponse. The recent advances in size- and shape-selective synthesis have enabled the design of quantum dot solar cells with photoconversion efficiencies greater than 5%. To make them competitive with other existing thin film or polycrystalline photovoltaic technologies, it is important to overcome kinetic barriers for charge transfer at semiconductor interfaces. This feature article focuses on the limitations imposed by slow hole transfer in improving solar cell performance and its role in the stability of metal chalcogenide solar cells. Strategies to improve the rate of hole transfer through surface-modified redox relays offer new opportunities to overcome the hole-transfer limitation. The mechanistic and kinetic aspects of hole transfer in quantum dot solar cells (QDSCs), nanowire solar cells (NWSCs), and extremely thin absorber (ETA) solar cells are discussed.

Origin of Catalytic Effect in the Reduction of CO2 at Nanostructured TiO2 Films

Abstract: Electrocatalytic activity of nanostructured TiO2 films toward the reduction of CO2 is probed by depositing a nanostructured film on a glassy carbon electrode. The one-electron reduction of CO2 in acetonitrile seen at an onset potential of −0.95 V (vs NHE) is significantly lower than the one observed with a glassy carbon electrode. The electrocatalytic role of TiO2 is elucidated through spectroelectrochemistry and product analysis. Ti3+ species formed when the TiO2 film is subjected to negative potentials have been identified as active reduction sites. Binding of CO2 to catalytically active Ti3+ followed by the electron transfer facilitates the initial one-electron reduction process. Methanol was the primary product when the reduction was carried out in wet acetonitrile.

Rate limiting interfacial hole transfer in Sb2S3 solid-state solar cells

Abstract: Transfer of photogenerated holes from the absorber species to the p-type hole conductor is fundamental to the performance of solid-state sensitized solar cells. In this study, we comprehensively investigate hole diffusion in the Sb2S3 absorber and hole transfer across the Sb2S3–CuSCN interface in the TiO2–Sb2S3–CuSCN system using femtosecond transient absorption spectroscopy, carrier diffusion modeling, and photovoltaic performance studies. Transfer of photogenerated holes from Sb2S3 to CuSCN is found to be dependent on Sb2S3 film thickness, a trend attributed to diffusion in the Sb2S3 absorber. However, modeling reveals that this process is not adequately described by diffusion limitations alone as has been assumed in similar systems. Therefore, both diffusion and transfer across the Sb2S3–CuSCN interface are taken into account to describe the hole transfer dynamics. Modeling of diffusion and interfacial hole transfer effects reveal that interfacial hole transfer, not diffusion, is the predominant factor dictating the magnitude of the hole transfer rate, especially in thin (<20 nm) Sb2S3 films. Lastly, the implications of these results are further explored by photovoltaic measurements using planar TiO2–Sb2S3–CuSCN solar cells to elucidate the role of hole transfer in photovoltaic performance.

How does a silar cdse film grow? Tuning the deposition steps to suppress interfacial charge recombination in solar cells

Abstract: Successive ionic layer adsorption and reaction (SILAR) is a popular method of depositing the metal chalcogenide semiconductor layer on the mesoscopic metal oxide films for designing quantum-dot-sensitized solar cells (QDSSCs) or extremely thin absorber (ETA) solar cells. While this deposition method exhibits higher loading of the light-absorbing semiconductor layer than direct adsorption of presynthesized colloidal quantum dots, the chemical identity of these nanostructures and the evolution of interfacial structure are poorly understood. We have now analyzed step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films using X-ray absorption near-edge structure analysis and probed the interfacial structure of these films. The film characteristics interestingly show dependence on the order in which the Cd and Se are deposited, and the CdSe–TiO2 interface is affected only during the first few cycles of deposition. Development of a SeO2 passivation layer in the SILAR-prepared films to fo...

Size-Dependent Energy Transfer Pathways in CdSe Quantum Dot–Squaraine Light-Harvesting Assemblies: Förster versus Dexter

Abstract: Energy transfer coupled with electron transfer is a convenient approach to mimic photosynthesis in light energy conversion. Better understanding of mechanistic details of energy transfer processes is important to enhance the performance of dye or quantum dot-sensitized solar cells. Energy transfer through both long-range dipole-based Forster resonance energy transfer (FRET) and short-range Dexter energy transfer (DET) mechanisms have been identified to occur between CdSe quantum dots (QDs) linked to a red-infrared-absorbing squaraine dye through a short thiol functional group (SQSH). Solutions of SQSH linked to CdSe were investigated through steady-state and time-resolved spectroscopy experiments to explore both mechanisms. Photoluminescence studies revealed that smaller QDs had higher energy transfer efficiencies than predicted by FRET, and femtosecond transient absorption experiments revealed faster energy transfer rates in smaller donor QD sizes. These findings supported a DET process dominating at sma...

Charge Transfer Mediation Through CuxS. The Hole Story of CdSe in Polysulfide

Abstract: Hole transfer to dissolved sulfide species in liquid junction CdSe quantum dot sensitized solar cells is relatively slow when compared to electron transfer from CdSe to TiO2. Controlled exposure of cadmium chalcogenide surfaces to copper ions followed by immersion in sulfide solution promotes development of the interfacial CuxS layer, which mediates hole transfer to polysulfide electrolyte by collection of photogenerated holes from CdSe. In addition, CuxS was also found to interact directly with defect states on the CdSe surface and quench emission characteristic of electron traps resulting from selenide vacancies. Together these effects were found to work in tandem to deliver 6.6% power conversion efficiency using Mn-doped CdS and CdSe cosensitized quantum dot solar cells. Development of an n–p interfacial junction at the photoanode–electrolyte interface in quantum dot solar cells unveils new means for designing high efficiency liquid junction solar cells.

Carbon nanohoops: excited singlet and triplet behavior of [9]- and [12]-cycloparaphenylene.

Abstract: Cycloparaphenylene molecules, commonly known as “carbon nanohoops”, have the potential to serve as building blocks in constructing carbon nanotube architectures. The singlet and triplet excited-state characteristics of [9]-cycloparaphenylene ([9]CPP) and [12]-cycloparaphenylene ([12]CPP) have now been elucidated using time-resolved transient absorption and emission techniques. The fluorescence quantum yields (Φ) of [9]CPP and [12]CPP were determined to be 0.46 and 0.83, respectively. Rates of nonradiative recombination (knr), radiative recombination (kr), and intersystem crossing (kisc) determined in this study indicate that radiative decay dominates in these nanohoop structures. The triplet extinction coefficient was determined through energy transfer with biphenyl, and the triplet quantum yield (ΦT) was calculated to be 0.18 and 0.13 for [9]CPP and [12]CPP, respectively. The rate of triplet state quenching by oxygen was measured to be 1.7 × 103 ([9]CPP) and 1.9 × 103 s–1 ([12]CPP). The excited-state dyn...

Organometal halide perovskites for transformative photovoltaics.

Abstract: O halide perovskite-based solar cells have recently emerged as a transformative photovoltaic (PV) technology. Two important journals, Science (DOI: 10.1126/ science.342.6165.1438-b) and Nature (http://www.nature. com/news/365-days-nature-s-10-1.14367), both highlighted perovskite photovoltaics as one of the major scientific breakthroughs of the year 2013. Power conversion efficiency attained with the hybrid organic−inorganic perovskite CH3NH3PbI3 has now exceeded 15%, making it competitive with thin-film PV technology. Decades-long basic research on dye-sensitized solar cells and quantum dot solar cells has now led to the development of perovskite PVs. The most attractive aspects of this technology are the simplicity of photoactive layer synthesis and application using benchtop approaches at temperatures less than 100 °C. A renewed enthusiasm has arisen among scientists in the field to continue developing economically viable next-generation PV technology. Recently, Perspective articles that highlight the evolution of perovskite PVs have identified areas of future growth for achieving efficiencies surpassing 20%. In this ACS Selects issue we present selected recent articles that focus on new methods and physical insights into the operation of organometal halide perovskite solar cells. Following the discovery of these organometal halide materials by Mitzi’s group in the 1990s, Miyasaka’s group uncovered their photoelectrochemical properties in 2009. Because of the instability of CH3NH3PbI3 in a solvent medium, research on this material remained dormant until solid-state solar cells were designed in 2012. The first attempt was by the Kanatzidis group using CsSnI3 as a solid hole conductor in dye-sensitized solar cells, followed by Graẗzel and co-workers utilizing CH3NH3PbI3 as a light absorber. 7 The CH3NH3PbI3 absorber can be easily prepared by dissolving equimolar amounts of methylammonium iodide (CH3NH3I) and lead(II) iodide (PbI2) solutions in anhydrous γ-butyrolactone at 70 °C. This solution, when spin-cast onto a mesoscopic titanium dioxide (TiO2) or aluminum oxide (Al2O3) film followed by drying at 70−80 °C, forms dark-colored crystalline CH3NH3PbI3 film with absorptions up to 800 nm (bandgap 1.5 eV). Some variations in synthesis include planar films without the mesoscopic templates, sequential exposure, and vapor-phase exposure of reactants. X-ray diffraction and Raman techniques have proven to be useful tools for characterizing the perovskite structure. The electronic structure and occupied energy levels of CH3NH3PbI3 deposited onto mesoporous TiO2 have been determined using photoelectron spectroscopy with hard X-rays. An important and useful feature of these organometal halide perovskite solar cells is the relatively high open-circuit voltage (VOC ≈ 1 V). New strategies are now being explored to boost the open-circuit voltage even higher using CH3NH3PbBr3. 11,12 For example, inclusion of chloride ions in CH3NH3PbBr3 films yields VOC as high as 1.5 V. Density functional theory is being applied to establish the semiconducting properties and find ways to manipulate band structure energetics. Recent efforts focus on identifying ambipolar charge-transport properties and the importance of spin−orbit coupling in organometal halide perovskites. In addition, a vapor-assisted solution process to construct polycrystalline perovskite thin films as well as nanometer-sized CH3NH3PbBr3 nanoparticles is facilitating new ways to probe the excited-state and charge-transport properties of this novel class of materials. The charge-separation, charge-recombination, and chargetransport properties of the organometal halide perovskite films coated on mesoscopic oxide films differ from those of other thin-film semiconductor PVs. To date, most of the reported studies employ spiro-OMeTAD as the hole conductor. Research is underway to explore alternate organic and inorganic hole conductors. Higher hole conductivity reported for inorganic hole conductors has been shown to be possible using cheaper and readily available materials such as CuI. A basic understanding of the hole transport properties is crucial for further development of perovskite solar cells. The papers presented in this ACS Selects collection focus on the physical chemistry aspects of the newly emerging field of organometal halide perovskites and provide key insights into their structural, optical, and charge-transport properties. Prashant V. Kamat, Deputy Editor Journal of Physical Chemistry Letters

CdSeS Nanowires: Compositionally Controlled Band Gap and Exciton Dynamics.

Abstract: CdS, CdSe, and ternary CdSexS(1–x) are some of the most widely studied II–VI semiconductors due to their broad range of applications and promising performance in numerous systems. One-dimensional semiconductor nanowires offer the ability to conduct charges efficiently along the length of the wire, which has potential charge transport benefits compared to nanoparticles. Herein, we report a simple, inexpensive synthetic procedure for high quality CdSeS nanowires where the composition can be easily modulated from pure CdSe to pure CdS by simply adjusting the Se:S precursor ratio. This allows for tuning of the absorption and emission properties of the nanowires across the visible spectrum. The CdSeS nanowires have a wurtzite crystal structure and grow along the [001] direction. As measured by femtosecond transient absorption spectroscopy, the short component of the excited state lifetime remains relatively constant at ∼10 ps with increasing Se; however, the contribution of this short lifetime component increa...

Sense and Shoot: Simultaneous Detection and Degradation of Low-Level Contaminants Using Graphene-Based Smart Material Assembly

Abstract: Smart material nanoassemblies that can simultaneously sense and shoot low-level contaminants from air and water are important for overcoming the threat of hazardous chemicals. Graphene oxide (GO) sheets deposited on mesoscopic TiO2 films that underpin the deposition of Ag nanoparticles with UV irradiation provide the foundation for the design of a smart material. The Ag particle size is readily controlled through precursor concentration and UV irradiation time. These semiconductor–graphene oxide–metal (SGM) films are SERS-active and hence capable of sensing aromatic contaminants such as 4-nitrobenzenethiol (4-NBT) in nanomolar range. Increased local concentration of organic molecules achieved through interaction with 2-D carbon support (GO) facilitates low-level detection of contaminants. Upon UV irradiation of 4-NBT-loaded SGM film, one can induce photocatalytic transformations. Thus, each component of the SGM film plays a pivotal role in aiding the detection and degradation of a contaminant dispersed in aqueous solutions. The advantage of using SGM films as multipurpose “detect and destroy” systems for nitroaromatic molecules is discussed.

Sequentially layered CdSe/CdS nanowire architecture for improved nanowire solar cell performance

Abstract: The power conversion efficiency of semiconductor nanowire (NW) based solar cells as compared to quantum dot solar cell (QDSC) has remained lower, and efforts to improve the photovoltaic performance of semiconductor NWs continue. We have now succeeded in using a layered architecture of CdS and CdSe NWs for improving the photovoltaic performance of nanowire solar cell (NWSC). The photoanode designed with sequentially deposited films of CdSe and CdS NWs delivered a power conversion efficiency of 1%. This efficiency of CdSe/CdS composite is an order of magnitude improvement over single nanowire system (CdS or CdSe) based solar cell. The improvement seen in the CdSe/CdS composite film is attributed to charge rectification and improvement of electron and hole separation and transport in the opposite direction. Impedance spectroscopy demonstrates the beneficial effect of type II structure in CdSe/CdS sequential deposition through lower transport resistance, which remains a dominating effect in dictating the over...

CdSe–Graphene Oxide Light-Harvesting Assembly: Size-Dependent Electron Transfer and Light Energy Conversion Aspects

Abstract: Excited-state interaction between CdSe quantum dots (QDs) of different sizes (2.3, 3.2, and 4.2 nm diameter) and graphene oxide (GO) was probed by depositing them as films on conducting glass electrodes. The emission of smaller CdSe QDs (2.3 nm) was quenched by GO three times faster than that of larger QDs (4.2 nm). Electrophoretic deposition allowed us to sequentially deposit single or multiple layers of different sized QDs and GO assemblies on conducting glass electrodes and to modulate the photoresponse in photoelectrochemical solar cells. Superior photoconversion efficiency through the incorporation of GO was attributed to improved charge separation in the composite assembly.

Heterogeneous Catalysis at Nanoscale for Energy Applications

Abstract: This book presents both the fundamentals concepts and latest achievements of a field that is growing in importance since it represents a possible solution for global energy problems. It focuses on an atomic-level understanding of heterogeneous catalysis involved in important energy conversion processes. It presents a concise picture for the entire area of heterogeneous catalysis with vision at the atomicand nanoscales, from synthesis, ex-situ and in-situ characterization, catalytic activity and selectivity, to mechanistic understanding based on experimental exploration and theoretical simulation. The book:

Driving charge separation for hybrid solar cells: photo-induced hole transfer in conjugated copolymer and semiconductor nanoparticle assemblies

Abstract: This work reports on the use of an internal electrostatic field to facilitate charge separation at inorganic–organic interfaces, analogous to those in hybrid solar cells. Systematic charge transfer studies show that the donor–acceptor charge transfer rate is highly sensitive to the direction of the internal electric field.

Overcoming the myths of the review process and getting your paper ready for publication

Abstract: Paper Ready for Publication T flood of scientific papers published daily across all scientific disciplines has resulted in the majority of these articles receiving less reader attention than they deserve. It is getting increasingly difficult for readers to keep up with all of the published papers in his/her discipline. Even in the major scientific journals, nearly 75% of the published articles receive citations that are below the journal’s impact factor, perhaps suggesting that many published papers do not receive sufficient attention from the average readership or simply they are not effective in communicating the results. (See, for example, Nature 2005, 435, 1003−1004. DOI: 10.1038/4351003b) Hence, it becomes the responsibility of the authors to take additional steps to make their paper effective as a scientific communication to a broad readership. A well-composed paper that can appeal to the general readership can draw favorable attention from editors and reviewers during the peer review process. (Tips on how to make your papers scientifically effective are available in an earlier editorial, “How to Make Your Next Paper Scientifically Effective” (http://pubs.acs.org/doi/abs/10.1021/jz4006916). We present in this Editorial some key steps in the review process for articles submitted to The Journal of Physical Chemistry Letters (JPCL) and provide some insight into how authors can work with the editors to improve their papers and facilitate their navigation through the peer review process. I just submitted my paper. What happens next? Every journal has its own submission criteria. It is therefore important for authors to pay attention to the requirements of the journal to which they are submitting their article and provide complete and accurate information. For JPCL, required information includes the manuscript title, coauthor names (entered in the same order as on the manuscript title page), author affiliations and current e-mail addresses, previous submission history, and correct manuscript files (in the proper format and with Supporting Information). Within hours of submission, our administrative personnel, who work almost around the clock in order to ensure rapid processing of each manuscript, check the submission information for accuracy and completeness. If the manuscript is complete and passes all of the administrative checks, it is forwarded to the Editor-in-Chief and Deputy Editor offices for evaluation. It should be noted that the staff performing the initial checks on the submissions is not involved in the scientific decisionmaking process, and no manuscripts are rejected during the administrative check. Manuscripts may, however, be “unsubmitted” if they fail to meet the journal submission criteria (i.e., the submissions are incomplete) and/or have significant formatting deficiencies. If an article is unsubmitted, authors are expected to address all deficiencies or concerns and resubmit the paper. In order to avoid a delay in the administrative check process, be sure to follow the Information for Authors (http://pubs.acs. org/page/jpclcd/submission/authors.html). In addition, if your paper was rejected by another journal, do not just turn around and resubmit the paper without f irst revising the manuscript to address feedback f rom referees, ensure that the manuscript has suf f icient relevance to physical chemistry (i.e., is within the scope of JPCL), and that the article is properly formatted for JPCL. What is the Editorial Review Process and how is it administered? After the administrative check, manuscripts arrive at the Editor-in-Chief and Deputy Editor offices and are assigned to an editor knowledgeable in the research topic. At JPCL, two editors carefully go through each manuscript and assess its scientific merit and relevance to physical chemistry. The editors read the title, abstract, presentation of results, and relevant citations within hours of submission. The editors specifically check to see whether the paper meets specific criteria, namely, urgency and timeliness of the research, significant advancement, physical chemistry scope, and likelihood of broad interest within the readership of the journal. On the basis of this initial review, a decision is made by the editor whether to move forward with an extended scientific review or to return the paper to the authors, citing any deficiencies. If a paper is returned to the author, the editor provides a statement explaining why the paper could not be considered for publication in JPCL. Because of the everincreasing review load placed on reviewers, many journals have adopted similar initial, editor-based review processes in their editorial offices. Frequently, papers are rejected after editorial review because the work is not sufficiently “urgent” for publication as a Letter. Even though the paper may be an excellent scientific report, if it does not advance the discipline in a timely way that strongly influences other researchers and/or stimulate immediate interest among the broad readership, the paper is considered to have insufficient urgency for publication as a Letter. Another common reason for rejection during the initial editorial review is that the work is outside of the scope of the journal, typically not providing new physical chemistry insight, which is a requirement for publication in JPCL. The editors often refer authors to submit such papers to specialized journals, the topic of which is based on the scope of the paper. Authors should keep in mind that references cited in a paper can be an excellent indicator of the f ield (and thus journal) to which the paper might appeal. For example, papers that primarily focus on the synthesis of new molecules or performance evaluation of devices may be better suited for publication in a more specialized journal. We welcome research crossing different disciplines, such as physics and/or materials science, provided that it is presented for the physical chemistry audience, including reviews of relevant literature and discussion of the results from a physical chemistry perspective. Another frequently encountered reason for immediate rejection is the premature nature of the research study. A single interesting observation or computational result is not sufficient for publication as a Letter. Observations need to be