Candidates For Solar Energy Conversion Research Articles

Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites.

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.

Improved Charge Separation and Transport with L-Aspartic Acid Derived Carbon-Doped g-C3N4 for Efficient Visible-Light Photocatalytic H2 Production

In recent years, polymeric graphitic carbon nitride (g-C3N4 termed as CN) is emerged as a favorable candidate for solar energy conversion. However, its practical applications are limited due to rapid...

Photocarrier transfer induced by Nδ− → Wδ+ in tungsten trioxide/carbon nitride for dual-path production of hydrogen peroxide towards ciprofloxacin degradation

Photo self-Fenton catalyst is a promising candidate for solar energy conversion and environmental remediation. Here we reported a Tungsten trioxide/carbon nitride (WO3/CN) in which the surficial amino groups on CN are inserted into the WO3 matrix, forming coordinate covalently Nδ− → Wδ+ in construction of an intimate S-scheme heterojunction. The intimantance promotes the transfer of photocarriers under light irradiation. The nanohybrids produced hydrogen peroxide (H2O2) in a rate about 20 times of pristine CN. A dual-path architecture in which H2O2 are produced via hole-water oxidation and electron-oxygen reduction was poposed. It is founded that ciprofloxacin also involved in production of H2O2 by their deprotonation to superoxide anions, and holes and hydroxyl radicals effectively attack the weak sites in skeleton of ciprofloxacin. This work suggests a great significance of strategy in self-producing of H2O2 in utilizing solar energy and molecular oxygen for water, particularly the surface water decontamination.

Nanorod length-dependent photodriven H2 production in 1D CdS-Pt heterostructures.

Colloidal quantum confined semiconductor-metal heterostructures are promising candidates for solar energy conversion because their light absorbing semiconductor and catalytic components can be independently tuned and optimized. Although the light-to-hydrogen efficiencies of such systems have shown interesting dependences on the morphologies of the semiconductor and metal domains, the mechanisms of such dependences are poorly understood. Here, we use Pt tipped 0D CdS quantum dots (with ∼4.6nm diameter) and 1D CdS nanorods (of ∼13.8, 27.8, 66.6, and 88.9nm average rod lengths) as a model system to study the distance-dependence of charge separation and charge recombination times and their impacts on photo-driven H2 production. The H2 generation quantum efficiency increases from 0.2% ± 0.0% in quantum dots to 28.9% ± 0.4% at a rod length of 28nm and shows negligible changes at longer rod lengths. The half-life time of electron transfer from CdS to Pt increases monotonically with rod length, from 0.7 ± 0.1 in quantum dots to 170.2 ± 29.5ps in the longest rods, corresponding to a slight decrease in electron transfer quantum efficiency from 92% to 81%. The amplitude-weighted average lifetime of charge recombination of the electron in Pt with the hole in CdS increases from 4.7 ± 0.4 µs in quantum dots to 149 ± 34 µs in 28nm nanorods, and the lifetime does not increase further in longer rods, resembling the trend in the observed H2 generation quantum efficiency. Our result suggests that the competition of the charge recombination process with the hole removal by the sacrificial electron donor plays a dominant role in the observed nanorod length dependent overall light driven H2 generation quantum efficiency.

Stability, optoelectronic and thermal properties of two-dimensional Janus α-Te2S

Motivated by recent progress in the two-dimensional (2D) materials of group VI elements and their experimental fabrication, we have investigated the stability, optoelectronic and thermal properties of Janus α-Te2S monolayer using first-principles calculations. The phonon dispersion and MD simulations confirm its dynamical and thermal stability. The moderate band gap (∼1.5 eV), ultrahigh carrier mobility (∼103 cm2 V−1 s−1), small exciton binding energy (0.26 eV), broad optical absorption range and charge carrier separation ability due to potential difference (ΔV = 1.07 eV) on two surfaces of Janus α-Te2S monolayer makes it a promising candidate for solar energy conversion. We propose various type-II heterostructures consisting of Janus α-Te2S and other transition metal dichalcogenides for solar cell applications. The calculated power conversion efficiencies of the proposed heterostructures, i.e. α-Te2S/T-PdS2, α-Te2S/BP and α-Te2S/H-MoS2 are ∼21%, ∼19% and 18%, respectively. Also, the ultralow value of lattice thermal conductivity (1.16 W m−1 K−1) of Janus α-Te2S makes it a promising material for the fabrication of next-generation thermal energy conversion devices.

Effect of High Dielectric SrF2 in TiO2 photoanode for Dye-Sensitized Solar Cell Applications

Dye-sensitized solar cells (DSSC) have been extensively investigated as promising candidate for solar energy conversion owing to their low cost, eco-friendly and high device efficiency. Among the other, photoanode is one of the key components in DSSC which defines its performance. Charge recombination and low light harvesting are the two major drawbacks of conventional TiO2 photoanode which limits the device efficiency. With this aim, the present work focused on the preparation of high dielectric SrF2 nanoparticles (ε’=6.844 x 106 at 1 Hz) and its study on incorporation with TiO2 photoanode with various weight percentages for device assembly. It can reduce the recombination by strong electrostatic shielding and increase the charge collection efficiency through interfacial polarization at dielectric-semiconductor interface shown in Fig.1. Improved power conversion efficiency (PCE) of 7.581% is obtained in 10 wt% SrF2:90 wt% TiO2 based photoanode which is 8.3% higher than the device efficiency of pure TiO2 based DSSC (6.997%). The interfacial charge transport kinetics of fabricated DSSCs are also explored using electrochemical impedance spectral (EIS) analysis. Low recombination resistance Rrec (49.9 Ω) in 10 wt% SrF2:90 wt% TiO2 based DSSC reveals the reduced recombination dynamics compared to other devices due to the optimized concentration of SrF2 incorporation in TiO2 photoanode for balancing charge injection and recombination. Keywords: DSSC; SrF2; Interfacial polarization; Dielectric constant and EIS Acknowledgement: This work was supported by Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT, Korea. (Grant number: 2019H1D3A1A01071183). It was also supported by the Technology Development Program to Solve Climate Changes of the National Research Foundation, funded by the Ministry of Science, ICT & Future Planning (No: NRF-2016M1A2A2940912). Fi gure.1. Dielectric plot as a function of angular frequency (Inset shows interfacial polarization at dielectric-semiconductor interface). Figure 1

Two-dimensional Janus Sn2SSe and SnGeS2 semiconductors as strong absorber candidates for photovoltaic solar cells: First principles computations

Two-dimensional materials provide new opportunities for the next generation of effective and ultrathin photovoltaic solar cells. Herein, we propose Janus monolayers of Tin monochalcogenides, especially Janus Sn2SSe (type TA) and SnGeS2 (type TB) nanosheets, as strong absorber candidates for solar energy conversion, referring to their excellent electronic and optical properties. Interestingly, based on the first-principles computations, both Janus Sn2SSe and SnGeS2 monolayers possess semiconductor character with indirect and moderate band gaps of 1.60 and 1.61eV, respectively. Accordingly, the considered systems, Sn2SSe and SnGeS2 single-layers, have high absorption coefficient, reaching up to 49.7 and 62.5μm−1, high optical conductivity of about 4513 and 3559Ω−1cm−1, as well as low reflectivity never exceed 34.6 and 38.5% in visible region, respectively. Additionally, the maximum photovoltaic efficiency of single-junction solar cells based on SnGeS2 and Sn2SSe nanosheets can reach as high as 27.47% and 28.12%, respectively. The present outstanding results would motivate both theoretical and experimental researchers to deepen the study of the potential applications of two-dimensional Janus materials based on Tin monochalcogenides in solar cell technology.

Formamidinium containing tetra cation organic–inorganic hybrid perovskite solar cell

ABX3 perovskites offer the advantage of manipulating its properties by introducing multiple cations in B-site. Over the years, researchers used mixed B-site perovskites in oxide electronics to tune their electrical, magnetic properties. Here we used the triple cations at B-site in formamidinium based organometallic halide perovskite solar cell (PSC) in order to improve its degradation behavior with respect to heat and moisture. We synthesized halide based two hybrid perovskites viz., formamidinium sodium bismuth lead iodide [NH2CHNH2(Na0.25Bi0.25)Pb0.5I3] and formamidinium potassium bismuth lead iodide [NH2CHNH2(K0.25Bi0.25)Pb0.5I3] using solution chemistry. In order to decrease the content of toxic lead in these perovskites, trivalent bismuth was incorporated in the Pb-site. Monovalent sodium and potassium were used to maintain the charge neutrality of B-site, which has the formal valence of + 2 in these ABI3 type perovskites. Both of these perovskites showed reasonable optical band gaps with good charge carrier lifetime suggesting it as potential candidates for solar energy conversion and provisionally we achieved power conversion efficiency η = 0.52%. Moreover, superior thermal and moisture stability in these perovskites were observed in periodical structural and spectral analysis carried out by XRD, UV–Vis spectroscopy, time-correlated single photon counting (TCSPC) over the period of one month. Furthermore, ultrafast carrier dynamics in these perovskites were unraveled using femtosecond transient absorption studies. Our transient absorption kinetics data suggested more auger recombination and faster free electron-hole recombination process in FKBPI compared to FNBPI, which corroborates well with better energy conversion efficiency obtained in FNBPI based solar cell.

On the electronic properties and performance of new nano thick solar material based on GeSe/SnS hetro-bilayer

Motivated by recent works dealing with electronic properties and high carrier mobility of monolayer materials and their potential applications in nano thick solar cells, we investigate the electronic properties and performance of new nano thick solar material based on GeSe/SnS hetro-bilayer. The calculations are performed using DFT calculations within GGA + vdW and HSE06 hybrid functional approximations. Our results indicate that this hetro-bilayer has a direct band gap of 1.48 $$ eV $$ , which is in the optimal range of the efficient single-junction solar cell, and forms the type-II band alignment in which $$ SnS $$ is the donor and $$ GeSe $$ is the acceptor. The values of $$ V_{oc } $$ , $$ FF $$ and $$ J_{sc} $$ using an external quantum efficiency with a limit of 100% are also calculated. Using Scharber model, the upper limit of power conversion efficiency, PCE, is estimated to be 18.74% which is higher than the reported efficiencies of hetro-bilayers. Another estimate of PCE via the descriptor model is found to be 28.83%. These findings make this hetero-bilayer a good candidate for solar energy conversion as an efficient nano-thick solar cell material, and optoelectronics applications as well.

Shape-Controlled Synthesis of Copper Indium Sulfide Nanostructures: Flowers, Platelets and Spheres.

Colloidal semiconductor nanostructures have been widely investigated for several applications, which rely not only on their size but also on shape control. CuInS2 (often abbreviated as CIS) nanostructures have been considered as candidates for solar energy conversion. In this work, three-dimensional (3D) colloidal CIS nanoflowers and nanospheres and two-dimensional (2D) nanoplatelets were selectively synthesized by changing the amount of a sulfur precursor (tert-dodecanethiol) serving both as a sulfur source and as a co-ligand. Monodisperse CIS nanoflowers (~15 nm) were formed via the aggregation of smaller CIS nanoparticles when the amount of tert-dodecanethiol used in reaction was low enough, which changed towards the formation of larger (70 nm) CIS nanospheres when it significantly increased. Both of these structures crystallized in a chalcopyrite CIS phase. Using an intermediate amount of tert-dodecanethiol, 2D nanoplatelets were obtained, 90 nm in length, 25 nm in width and the thickness of a few nanometers along the a-axis of the wurtzite CIS phase. Based on a series of experiments which employed mixtures of tert-dodecanethiol and 1-dodecanethiol, a ligand-controlled mechanism is proposed to explain the manifold range of the resulting shapes and crystal phases of CIS nanostructures.

Reactive Inorganic Vapor Deposition of Perovskite Oxynitride Films for Solar Energy Conversion.

The synthesis of perovskite oxynitrides, which are promising photoanode candidates for solar energy conversion, is normally accomplished by high-temperature ammonolysis of oxides and carbonate precursors, thus making the deposition of their planar films onto conductive substrates challenging. Here, we proposed a facile strategy to prepare a series of perovskite oxynitride films. Taking SrTaO2N as a prototype, we prepared SrTaO2N films on Ta foils under NH3 flow by utilizing the vaporized SrCl2/SrCO3 eutectic salt. The SrTaO2N films exhibit solar water-splitting photocurrents of 3.0 mA cm−2 at 1.23 V vs. RHE (reversible hydrogen electrode), which increases by 270% compared to the highest photocurrent (1.1 mA cm−2 at 1.23 V vs. RHE) of SrTaO2N reported in the literature. This strategy may also be applied to directly prepare a series of perovskite oxynitride films on conductive substrates such as ATaO2N (A = Ca, Ba) and ANbO2N (A = Sr, Ba).

Structural, electronic and optical properties of RbSnCl3: A first-principles calculation

The structural, electronic and optical properties of RbSnCl3 are investigated by the first-principles calculations. Two new phases of Cm and Imm2 are predicted and the phonon spectrum are analyzed, which shows that the two phases are all dynamically stable. The band edge positions show that the two phases conform to the criteria of photocatalysts for water splitting, and strains are added to the two phases. The results show that strains can effectively tune the bandgaps and RbSnCl3 is potential candidate for solar energy conversion and photocatalytic water splitting.

Insights Into Interfacial Interaction and Its Influence on the Electronic and Optical Properties of Two‐Dimensional WS2/TX2CO2 (TX = Ti, Zr) van der Waals Heterostructures

Two‐dimensional (2D) transition metal dichalcogenides (TMDs), carbides (MXenes), and their heterostructures showcase several key properties that can address emerging energy needs, in particular for solar energy conversion and storage devices. Understanding the fundamental science of these heterostructures is paramount to designing them with desirable properties. Using a detailed theoretical study of 2D WS2/TX2CO2 (TX = Ti, Zr) van der Waals heterostructure, as a typical case, based on density functional theory, we firstly reveal that the interfacial interaction is mainly dependent on their stacking configuration and/or TX atom. Compared to that of individual, the band gap of heterostructure is obviously reduced. The strong absorption in the ultraviolet and visible‐light region, the type‐II staggered band alignment at the interface make the 2D WS2/TX2CO2 heterostructures promising candidates for photocatalysis, photodetector, and solar energy harvesting and conversion. Moreover, these heterostructures can also be effective solar cell materials with theoretical power conversion efficiency up to 11.30%, suggesting that they are potential candidates for solar energy conversion. This work provides the insight into the interfacial interaction and its effects, and can facilitate the applications of TMDs and MXenes.

Preparation and optical characterization of β-MnO2 nano thin films for application in heterojunction photodiodes

The present work shows that manganese dioxide (β-MnO2) nano films can be applied as a potential candidate for solar energy conversion. β-MnO2 nano thin films were successfully grown on glass and quartz substrates using thermal evaporation technique. The structural properties of as-deposited and annealed thin films were analyzed using both X-ray diffraction and field emission scanning electron microscopy techniques. The spectroscopic characterizations of β-MnO2 nano thin films with different film thickness were studied using spectrophotometric technique in the wavelength of 200–2400 nm. The optical constants of these films were calculated and showed variation with film thickness and annealing temperature. Wemple -DiDomenico oscillator model was applied in the non-absorbing region of refractive index spectrum in order to evaluate the dispersion parameters. The nonlinear optical parameters were calculated using the linear optical parameters. The annealing temperature considered to be a good tool for enhancement of the nonlinear optical parameters of β-MnO2 nano films. Unraveling the correlated optical properties with the photoresponse characterizations of β-MnO2 nano films opens the avenue to design and fabricate heterojunction photodiodes based on β-MnO2 nano-films. The photoresponsivity, photoconductivity and specific detectivity of fabricated Au/β-MnO2/p-Si/Al photodiodes were studied.

Molecular design of interfacial layers based on conjugated polythiophenes for polymer and hybrid solar cells

AbstractIn the past two decades, bulk heterojunction organic photovoltaic (OPV) devices have emerged as attractive candidates for solar energy conversion due to their lightweight design and potential for low‐cost, high‐throughput, solution‐phase processability. Interfacial engineering is a proven efficient approach to achieve OPV devices with high power conversion efficiencies. This mini‐review provides an overview of the key structural considerations necessary when undertaking the molecular design of conjugated polyelectrolytes, for application as interfacial layers (ILs). The different roles of ILs are outlined, together with the advantages and disadvantages of competing classes of IL materials. Particular emphasis is placed on the design and synthesis of water‐soluble polythiophene‐based IL materials and the influence of their structural characteristics on their performance as a promising class of IL material. Finally, the challenges and opportunities for polythiophenes as IL materials for OPV devices and other solution‐processed solar cell technologies (e.g. perovskite solar cells) are discussed. © 2017 Society of Chemical Industry

A many-body GW + BSE investigation of electronic and optical properties of C2N

A recently synthesized layered material C2N was investigated based on many-body perturbation theory using the GW plus Bethe-Salpeter equation approach. The electronic band gap was determined to be ranging from 3.75 to 1.89 eV from the monolayer to the bulk. Significant GW quasiparticle corrections, of more than 0.9 eV, to the Kohn-Sham band gaps from the local density approximation calculations are found. Strong excitonic effects play a crucial role in optical properties. We found large binding energies of greater than 0.6 eV for bound excitons in few-layer C2N, while it is only 0.04 eV in bulk C2N. All the structures exhibit strong and broad optical absorption in the visible light region, which makes C2N a promising candidate for solar energy conversion, such as photocatalytic water splitting.

Metal-Organic Frameworks as Promising Photosensitizers for Photoelectrochemical Water Splitting.

Ti-based metal-organic frameworks (MOFs) are demonstrated as promising photosensitizers for photoelectrochemical (PEC) water splitting. Photocurrents of TiO2 nano wire photoelectrodes can be improved under visible light through sensitization with aminated Ti-based MOFs. As a host, other sensitizers or catalysts such as Au nanoparticles can be incorporated into the MOF layer thus further improving the PEC water splitting efficiency.

Photosensitive oxide semiconductors for solar hydrogen fuel and water disinfection

Hydrogen is expected to become a commonly used energy carrier on the global scale in the near future. However, hydrogen as a fuel is environmentally friendly only when generated from water using renewable energy, such as solar energy. Therefore, intensive research aims to develop a new generation of solar materials, which may be used for the production of hydrogen fuel from water using solar energy. The highly promising candidates for solar energy conversion are photosensitive oxide semiconductors (POSs), particularly the TiO2-based semiconductors, which may be used for converting solar energy into the chemical energy required for hydrogen generation from water, as well as water purification (removal of microbial agents and toxic contaminants from water). The present work considers an R&D strategy for developing TiO2-based systems capable of converting solar energy into the chemical energy via water oxidation. The effect of surface versus bulk semiconducting properties on the performance of POSs is considered in terms of partial and total water oxidation. The progress requires modification of the key performance-related properties (KPPs) in order to enhance the light-induced reactivity of the POSs with water. The most recent approach in the development of POSs with enhanced performance is deposition of metallic islets of different size and shape in order to induce a plasmonic effect. The development of high-performance POSs can be achieved through a multidisciplinary approach. It is shown that defect disorder has a critical effect on the light-induced reactivity of POSs and the solar energy conversion. Therefore, defect engineering may be applied in the development of high-performance POSs. This work considers the hurdles in the development of high-performance POSs for specific applications and formulates the key questions that must be addressed to overcome these hurdles. The concepts developed for TiO2 may be expanded for other metal oxides.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6–20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS–CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Unravelling the correlated electronic and optical properties of BaTaO2N with perovskite-type structure as a potential candidate for solar energy conversion.

We report on the first principles calculation of the electronic, structural and optical properties of BaTaO2N, using density functional theory (DFT) and finite difference time domain (FDTD) methods. Band structure calculations were performed to calculate the direct and indirect bandgaps of the material. Density of states and Mulliken charge analysis as well as the electronic contour maps were established to determine the type of bonding and hybridization between the various electronic states. The dielectric constant, reflectivity, absorption, optical conductivity and energy-loss function were also calculated. Moreover, FDTD was used to investigate the optical properties of a larger and more reliable structure of BaTaO2N powder in good agreement with the reported experimental parameters. The calculated electronic, structural and optical properties showed the potential of BaTaO2N for solar energy conversion and optoelectronic applications.