Solar Conversion Research Articles

Heavy-Metal-Free Colloidal Quantum Dots: Progress and Opportunities in Solar Technologies.

Colloidal quantum dots (QDs) hold great promise as building blocks in solar technologies owing to their remarkable photostability and adjustable properties through the rationale involving size, atomic composition of core and shell, shapes, and surface states. However, most high-performing QDs in solar conversion contain hazardous metal elements, including Cd and Pb, posing significant environmental risks. Here, a comprehensive review of heavy-metal-free colloidal QDs for solar technologies, including photovoltaic (PV) devices, solar-to-chemical fuel conversion, and luminescent solar concentrators (LSCs), is presented. Emerging synthetic strategies to optimize the optical properties by tuning the energy band structure and manipulating charge dynamics within the QDs and at the QDs/charge acceptors interfaces, are analyzed. A comparative analysis of different synthetic methods is provided, structure-property relationships in these materials are discussed, and they are correlated with the performance of solar devices. This work is concluded with an outlook on challenges and opportunities for future work, including machine learning-based design, sustainable synthesis, and new surface/interface engineering.

SCAPS-1D simulation and First-principles calculation of CsSnCl3 hole transport layer-free perovskite solar cells based on gradient doping

As the photovoltaic industry continues to evolve perovskite materials that are inorganic, non-toxic, and do not require a hole transport layer are particularly promising. However, such perovskite solar cells (PSCs) generally do not perform well. Therefore, we propose a gradient doped CsSnCl3 PSCs without hole transport layer (HTL) and investigate the optical and electrical properties of its absorption layer using first principles calculations. We further simulate and optimize this PSCs using SCAPS-1D software, focusing on various factors such as charge transport layer materials, perovskite layer thickness, doping concentration, and working temperature. Our comprehensive analysis also takes changes in the internal electric field and band structure in consideration. The study's results demonstrate that gradient doping creates an additional electric field, significantly improving the solar cell's photovoltaic conversion efficiency. When G=100, even with only two sublayers of gradient doping, a considerable performance boost is observed. The performance of optimized device is as follows: Voc = 1.1841 V, Jsc = 30.13298 mA/cm2, FF = 90.08 %, and PCE = 32.14 %. Compared with the initial PSC's efficiency of 13.93 %, it has significantly improved by 130.7 %. This research provides unique insights and guidance for the future design and manufacture of efficient, all-inorganic, non-toxic PSCs HTL-free.

Synergistic photovoltaic performance of DSSCs based on ZnO charge transport layers, counter electrodes and C. annuum and T. indica as natural dyes

Twelve Dye-Sensitized Solar Cells (DSSCs), in terms of three categories, were designed and fabricated employing ZnO-based charge-transport layers, Capsicum annuum (C. annuum) and Tamarindus indica (T. indica) as natural dyes and, Graphite and PEDOT:PSS as counter electrodes. J-V curves and cell efficiencies (η) of all DSSC combinations were measured. Among DSSCs in category-1 maximum and minimum η of 1.25% and 0.47% were estimated for FTO/ZAN37/C. annuum(dye)/HSE/Graphite and FTO/ZAN37/T. indica (dye)/HSE/Graphite, respectively. In the case of category-2, the DSSCs FTO/ZAN55/T. indica (dye)/HSE/PEDOT:PSS showed 0.60% efficiency and FTO/ZAN55/T. indica (dye)/HSE/Graphite revealed as high as η = 1.07%. Similarly, for category 3, the maximum η = 1.71% and minimum η = 0.32% were recorded for the DSSC’s combinations; FTO/ZAN(SFM)/C. annuum(dye)/HSE/Graphite and FTO/ZAN(SFM)/C. annuum(dye)/HSE/PEDOT:PSS. Based on charge transporting layers, dyes, and counter electrodes, a synergistic effect was developed in each considered DSSC led to a mechanism of the solar power conversion process.

A novel solar-aided NOx removal system in peaking power plants

Solar–coal hybrid power generation achieves the production of efficient, clean, and low-carbon electricity. The association between solar heat and selective catalytic reduction NOx removal (SCR de-NOx) can lead to the development of a novel solar-aided NOx removal system for peaking power plants. In this study, a novel system was proposed, in which large amount of flat-plate and small amount of trough solar energies were integrated to optimise the SCR de-NOx and energy utilisation in the boiler tail. Thermodynamic, NOx removal, and economic analyses were performed. For a typical peaking unit, the proposed system produced 14.6 MWe of solar-generated electric power and exhibited a high solar-to-electricity efficiency of 30.15 %. The integrated solar heat significantly increased the SCR de-NOx temperature and NOx removal efficiency. Based on its outstanding solar conversion performance, the proposed system achieved a net annual benefit (NAB) of 24.01 million Chinese yuan (CNY) and maintained a low cost of solar-generated electricity (COEs) of 0.56 CNY/kWh. Based on cascade utilisation of solar thermal energy, the proposed system achieved high performance under all loads and significantly improved the NOx removal performance under low and medium loads, especially for peaking power plants.

MOFs-derived S-scheme ZnO/BiOBr heterojunction with rich oxygen vacancy for boosting photocatalytic CO2 reduction

In this paper, a MOFs-derived S-scheme ZnO/BiOBr heterojunction photocatalyst was constructed by a one-step calcination method. It was found that the dodecahedral ZnO was well attached to the BiOBr hollow rods in ZnO/BiOBr composites, which could simultaneously introduce oxygen vacancies and enhance interfacial interactions. The photocatalytic CO2 reduction results exhibited that ZnO/BiOBr, without adding any sacrificial agent and photosensitiser, produced CO and CH4 at rates of 21.13 μmol·g−1·h−1 and 2.2 μmol·g−1·h−1 under simulated sunlight, with a CO selectivity of 74.34 %, which was 6.35 and 4.07 times higher than that of the original BiOBr as well as the original ZnO 4.14 and 1.98 times, respectively. The optimised ZnO/BiOBr has excellent photocatalytic CO2 reduction performance. The ZnO/BiOBr photocatalyst has excellent stability after 5 cycles. The unique heterostructures and matched energy band potentials between ZnO and BiOBr provided close interfacial contacts, a large number of active sites and effective charge transferred for photocatalytic CO2 reduction. Furthermore, the mechanism of photocatalytic CO2 reduction for S-scheme ZnO/BiOBr heterojunction was also proposed. Therefore, the MOFs-derived ZnO/BiOBr composites had the potential to be used as photocatalyst for CO2 reduction, providing a rational design idea for solar energy-driven CO2 conversion of MOFs-structured photocatalysts.

Boosting photoelectron transfer by Fermi and doping levels regulation in carbon nitride towards efficient solar-driven hydrogen production

The exploration of efficient photosystems with fast carrier dynamics is an important pursuit for solar conversion into hydrogen energy, while tremendous challenges remain since the intrinsic relationship between the band structure and the charge transfer behavior in semiconductors is still elusive. Towards this, P doped graphitic carbon nitride (P-g-C3N4) is fabricated as a prototype photocatalyst with P existing in P − N = C state. Through tuning the content of P to modulate the electronic donor concentration, the Fermi level of g-C3N4 is unidirectionally regulated from below to above the doping level induced by P. And it is revealed that the relative position of Fermi level vs. doping level plays a crucial role in determining the charge migration dynamics, where only a doping state near the Fermi level can act as the most efficient electron trap to prolong carrier lifetime. Accordingly, the precisely tailored P-g-C3N4 achieves a superior apparent quantum efficiency (AQE) of 5.7 % at 420 nm in overall water splitting that is among the highest levels of current photosystems. Our findings offer an innovative strategy for band structure regulation toward efficient photocatalysis.

Photoelectrochemical catalytic CO2 reduction enhanced by In-doped GaN and combined with vibration energy harvester driving CO2 reduction

Photoelectrochemical (PEC) technology seamlessly integrates and optimizes the merits of photocatalysis and electrocatalysis, facilitating charge separation and enhancing solar conversion efficiency. It stands out as a promising approach for CO2 treatment. GaN as III-Ⅴ semiconductor, has garnered substantial attention in the realm of PEC CO2 reduction reactions (RR). In this study, GaN and In/GaN micro-rods were prepared via straightforward hydrothermal synthesis. Attaining a current density of approximately 10 mA/cm2 and CO Faradaic Efficiency (FE) of ∼45 % at −0.75 VRHE (Reversible Hydrogen Electrode, RHE), In/GaN exhibited exceptional stability over a 2 h PEC CO2 RR. The introduction of In into GaN significantly augmented CO2 adsorption capacity and light harvesting. Additionally, Density Functional Theory (DFT) calculations elucidated that In-doped GaN can diminish the adsorption of intermediate CO, favoring subsequent CO desorption. Furthermore, the N-vacancy increased with In doping, resulting in a rise in the number of unpaired electrons, facilitating carrier transport. Herein, vibration energy harvester was introduced to drive CO2 RR, marking a significant advancement in development of PEC CO2 RR for future green energy applications.

Host sensitized down conversion emission in KSrVO4:Yb3+− A potential thermally stable phosphor for solar cell applications

This work reports the successful synthesis of an efficient near infra-red (NIR) emitting KSrVO4:Yb3+ phosphor using the combustion method. The X-ray diffraction technique (XRD) confirmed the orthorhombic phase of a material whereas X-ray photoelectron spectroscopy (XPS) analyzed the elemental makeup and chemical states of the phosphor components. Photoluminescence (PL) analysis revealed that the phosphor exhibit superior thermal stability and emit in the NIR region when activated by near-UV light. An upsurge in emission intensity occurs upon the incorporation of Bi3+ as a co-dopant. Using diffuse reflectance spectra (DRS), optical band gap, metallization constant, and refractive index were computed for all ion concentrations in KSr(1-x)VO4:xYb3+ (0 ≤x ≤ 0.06). For the optimized concentration of Yb3+ into the host, numerical values of these parameters were also estimated. The studies reveal that the produced material may be applied as a solar spectrum converter to improve the efficiency of crystalline silicon (c-Si) solar cells.

Improving Charge Transfer Beyond Conventional Heterojunction Photoelectrodes: Fundamentals, Strategies and Applications

AbstractPhotoelectrochemical (PEC) cells are regarded as a promising approach to convert sunlight to chemical fuels, whereas the serious photo‐induced charge recombination of the semiconductor photoelectrode hinders its solar conversion efficiency. Over the past few decades, designing and constructing heterojunction photoelectrodes via thermodynamically favorable charge transfer have been proven to be effective in boosting photo‐induced charge separation. However, the conventional heterojunction construction strategy generally introduces incompatible, nonconformal, or defective interfaces, leaving considerable room to improve the thermodynamically favorable charge transfer efficiency in the heterojunction photoelectrodes. To compensate for the unsatisfied charge transfer efficiency, some novel strategies, such as grain boundary engineering, band gap engineering, field‐effected engineering, etc., are adopted to provide additional charge transfer driving force, which significantly improves the charge transfer efficiency. In this review, these novel strategies are discussed beyond the conventional heterojunction construction, and the prospects for the development and applications of heterojunction photoanodes are also proposed.

Thermoradiative coupling graphene-based thermionic solar conversion

Thermionic conversion, due to its simple solid-state structure capable of converting heat to electricity directly, is promising for concentrated solar power. However, because of the extremely high cathode temperature, a large portion of the heat is lost to the environment. The paper introduces a novel concept of selective thermoradiative-graphene thermionic conversion (STR-GTI) that involving a combined control of photon and electron emission to modify the radiation dissipation. A detailed thermodynamic model is developed to evaluate the energy transfer irreversibility of STR-GTI solar conversion. The results demonstrate that the selective themoradiative photon emission and graphene thermionic electron emission effects synergistically reduce internal irreversible losses in the STR-GTI system, leading to a maximum energy efficiency of 34.34 % at a concentration ratio of 425, cathode work function of 1.8 eV and thermoradiative bandgap of 0.2 eV. The STR-GTI system outperforms both individual GTI and STR converters in terms of exergy efficiency and entropy production minimization. It exhibits a remarkable 102.03 % increase in exergy efficiency compared to the STR & GTI system at a thermoradiative voltage of −0.14 eV, accompanied by a 28.56 % reduction in exergy loss and a 37.83 % decrease in entropy production. The combination of narrowing the spectral radiation bandwidth and significant electron emission capabilities of graphene contribute to the system’s resilience against solar radiation fluctuations.

Structure-Property Correlations in CZTSe Domains within Semiconductor Nanocrystals as Photovoltaic Absorbers.

Semiconductor nanocrystals (NCs) are promising materials for various applications. Two of four recently identified CuαZnβSnγSeδ (CZTSe) domains demonstrate metallic character, while the other two exhibit semiconductor character. The presence of both metallic and semiconductor domains in one NC can hugely benefit future applications. In contrast to traditional band gap studies in the NC community, this study emphasizes that NC domain interfaces also affect the electronic properties. Specifically, the measured band gap of a tetrapod-shaped CZTSe NC is demonstrated to originate from two specific domains (tetragonal I and monoclinic P1c1 Cu2ZnSnSe4). The heterojunction between these two semiconductor domains exhibits a staggered type-II band alignment, facilitating the separation of photogenerated electron-hole pairs. Interestingly, tetrapod NCs have the potential to be efficient absorber materials with higher capacitance in photovoltaic applications due to the presence of both semiconductor/semiconductor interfaces and metal/semiconductor "Schottky"-junctions. For the two photo-absorbing domains, the calculated absorption spectra yield maximum photon-absorption coefficients of about 105 cm-1 in the visible and UV regions and a theoretical solar power conversion efficiency up to 20.8%. These insights into the structure-property relationships in CZTSe NCs will guide the design of more efficient advanced optical CZTSe materials for various applications.

Mechanically strong, healable, and recyclable supramolecular solid–solid phase change materials with high thermal conductivity for thermal energy storage

Conventional polymeric solid–solid phase change materials (SSPCMs) have garnered significant attention in the development of state-of-the-art latent heat storage (LHS) systems. However, the industrial application of polymeric SSPCMs is compromised by inferior mechanical properties and intrinsic low thermal conductivity. In addition, they are unable to be recycled and self-healed due to permanently cross-linked structures. In this study, a series of healable and recyclable supramolecular SSPCMs (PEG4K-Bx-PEG6K), possessing robust tensile strength (∼22.90 MPa), excellent strain-at-break (∼733.62 %), and high toughness (∼120.05 MJ/m3), are designed and developed by incorporating dynamic boroxines and hydrogen bonds. Because of the reversibility of dynamic boroxines and hydrogen bonds, the PEG4K-Bx-PEG6K was able to be healable and conveniently processed into packaging bag. More importantly, the PEG4K-Bx-PEG6K also possessed high thermal storage capacity (98.03 J/g), and excellent thermal shape memory capability. To achieve efficient heat transfer, an orientated solar thermal composite with high thermal conductivity was fabricated by compression-induced repetitive stacking of oriented graphene nanosheets (GNs) layers in PEG4K-Bx-PEG6K. Thanks to the efficient heat conduction of oriented GNs layers in the composite, the directional thermal conductivity of composite was up to 3.639 W/mK at 5 wt% loading of GNs. Combining the above excellent heat conduction, the solar thermal composite developed in this work offered efficient solar thermal conversion, fast transportation and storage of the harvested thermal energy.

Solar-driven high-performance biomass porous carbon for efficient CO2 capture

Temperature swing adsorption (TSA) based on solid adsorbents is an efficient CO2 capture technology, but the temperature swing process is energy-intensive. Utilizing solar energy to regenerate adsorbents during the CO2 swing adsorption process can decrease energy consumption. This work reports a novel high-performance biomass porous carbon for efficient CO2 capture and separation in the solar-driven TSA process. Inspired by the distinctive internal expansion structure of succulents, the adsorbent is synthesized using succulents as precursors with a large specific surface area (1715 m2/g) and high solar absorbance (90.38 %), resulting in high CO2 adsorption capacity and solar thermal conversion capacity. It achieves a remarkable working capacity of 30.94 mg/g at a low desorption temperature (60 °C) in the solar-driven TSA process with a light intensity of 600 W/m2, 80.7 % higher than commercial activation carbon. The proposed biomass porous carbon derived from succulent plants has substantial potential for application in the solar-driven TSA process.

Engineering single-atom catalysts on triazine-based covalent organic frameworks for enhanced photocatalytic performance in N2 reduction

The solar conversion of nitrogen to ammonia is a green, sustainable, and promising way to fix nitrogen. However, designing a photocatalyst with high activity, selectivity, and stability for the N2 reduction reaction (NRR) is challenging because of the slow inert activation of N2 and competitive hydrogen evolution reaction (HER). Herein, a single metal site anchored to a triazine-based covalent organic framework (Tr-COF) backbone (named TM@Tr-COF; TM = Fe, Co and Ni) is fabricated for high-performance catalytic N2 reduction. Density functional theory calculations show that the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF can effectively activate N2 and reduce it to NH3 via the electron “acceptance–donation” process. Meanwhile, the NRR occurs via the enzymatic pathway on the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF with a limiting potential of 0.38 V, 0.58 V and 0.54 V, respectively. Furthermore, the anchoring of Fe/Co/Ni on the Tr-COF allows the Tr-COF to be adjusted to the appropriate edge position and visible light-absorption region, indicating that the system may be a promising and efficient photocatalyst. Compared with other competitive reactions, the system exhibits high selectivity for NH3 production and inhibits competitive HERs. These findings have considerable implications for innovatively designing highly active single-atom catalysts supported by COFs.

2D Porphyrin-Based Covalent-Organic Framework/PEG Composites: A Rational Strategy for Photocatalytic Hydrogen Evolution.

Two-dimensional porphyrin-based covalent-organic frameworks (2D-por-COFs) have gained significant attention as attractive platforms for efficient solar light conversion into hydrogen production. Herein, it is found that introducing transition metal zinc and polyethylene glycol (PEG) into 2D-por-COFs can effectively improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rate of ZnPor-COF is 2.82 times higher than that of H2Por-COF. Moreover, ZnPor-COF@PEG has the highest photocatalytic hydrogen evolution efficiency, which is 1.31 and 3.7 times that of pristine ZnPor-COF and H2Por-COF, respectively. The filling of PEG makes the layered structure of COFs more stable. PEG reduces the distortion and deformation of the carbon skeleton after the experiment of photocatalytic hydrogen evolution. The layered stacking and crystallization of 2D-por-COFs are also enhanced. Meanwhile, the presence of PEG also accelerates the transfer of excited electrons and enhances the photocatalytic hydrogen evolution activity. This strategy will provide valuable insights into the design of 2D-por-COFs as efficient solid photocatalysts for solar-driven hydrogen production.

Study of Photogalvanic Effect by using Marigold Flower as Natural Photosensitizer, Xylose as Reductant and Tween 80 as Surfactant for Solar Radiation Conversion and Storage

Objective: A study work plan has been put up for methodical work in the field of solar energy Photogalvanic (PG) cells. It was suggested and required to do experiments with PG cells in sunlight conditions. Improving the conversion of solar energy into electricity and storing it in PG cells is the goal of our study. Method: An H-shaped glass tube with two arms was manufactured using the specially developed PG (Figure 1) cell. Many characteristics of a PG cell with an MG+D-Xylose+Tween-80 system was investigated. Findings: The open circuit voltage, voltage at dark, photopotential (PP), and photocurrent (PC) recorded in this investigation are 1080.00 mV, 165.00 mV, 915.00 mV, and 674.00 µA, respectively. The Fill Factor (FF) and Conversion Efficiency (CE) that were observed 1.891% and 0.2732, respectively. Novelty: Through the adjustment of PG cells' numerous parameters, the effects of solar energy were investigated. Based on the aforementioned results, PG systems have demonstrated through experimentation that they are an effective system and should be further investigated, particularly with regard to improving solar energy output and storage. Keywords: D-Xylose, Tween - 80, Marigold, Photocurrent, Natural dye

Investigation on implementing the swarm nano grid system for effective utilization of solar-powered agro-industries

The agro-industry is the backbone of the global economy, even in the twenty-first century. The agro-industry would not be what it is now without irrigation. The production and use of renewable energy in this sector of the agricultural economy have also expanded rapidly in recent years. Base-load power production and conversions dominate the literature. This research examines user concerns. The swarm nano grid system fixes this. The pulse width modulation (PWM) sinusoidal inverter converted stable DC power from the bidirectional DC-DC converter into sinusoidal AC voltage for the irrigation pump induction motor. Solar panels, batteries, and converters are costly, but they pay off. The nano grid distributes excess power generated during low demand to local loads. This technique works well when the load can be disconnected from the power grid. MATLAB is used to keep an eye on the reliability and efficiency of the induction motor. In the first simulation, solar power generation is modeled using the MATLAB Simulink software in two distinct modes. A PWM sinusoidal inverter that is driven by solar energy is what provides power to the 5.67 kW induction submersible motor. The simulation result provides a conceptual model of how induction motors powered by renewable energy sources function in practice.

High transmittance BiVO4 thin-film photoanodes by reactive magnetron sputtering for a photovoltaic-photoelectrocatalysis water splitting system

As the system with the highest solar hydrogen conversion efficiency, the further improvement of photovoltaic-photoelectrocatalysis (PV-PEC) efficiency is dependent on the light transmittance, activity and stability of the photoanode. Here, a highly permeable BiVO4 thin film was fabricated through controlled magnetron sputtering. The thickness of the thin film was merely 345 nm, while its transmittance in the visible light range reached as high as 70%. Moreover, large-scale production of such films could be achieved. By incorporating NiFeOx oxygen extraction cocatalyst, under AM 1.5G illumination, the photocurrent density at 1.23 V on reversible hydrogen electrode (RHE) increased to 4.2 mA cm−2 and the incident photon-current conversion efficiency reached 70%. A PV-PEC system was designed to efficiently harness sunlight by integrating the photoanode with a solar photovoltaic panel. Upon connection with the solar photovoltaic panel (with an efficiency of only 7%), spontaneous water decomposition could be achieved, resulting in a solar-to-hydrogen conversion efficiency (ηSTH) of 4.2% for the series system. This study contributes to the realization of cost-effective and highly efficient PV-PEC hydrogen production.

Carbon nanotubes reinforced poly (methyl methacrylate) polymer composites for the application as classic performance quasi-solid-state dye-Sensitized solar cell electrolytes

Our study aimed to evaluate the efficiency of solar power systems by developing dye-sensitized solar cells (DSSCs) with an electrolyte of carbon nanotubes (CNTs) dispersed in poly (methyl methacrylate) (PMMA). Photovoltaic and impedance spectral studies showed that a polymer electrolyte with 3% carbon nanotubes resulted in an efficiency of solar power conversion of 7.40% and a photovoltaic current per unit cross-sectional area of 17.13 mA/cm2 in DSSCs. The optimal distribution of CNT fillers decreased the charge recombination of the titanium dioxide-dye-CNT-PMMA electrolyte surface. The X-ray diffraction spectrum showed characteristic peaks of PMMA and CNT at 28.6° and 63.0°, respectively, obtained in pure form and composites with dispersed carbon nanotubes. The peak intensity increased with the addition of CNTs in the polymer. A Fourier transform infrared spectroscopy investigation revealed the bonding within the CO and CH of PMMA and CNT to the polymer composite. The dielectric constant increased from 2.9 to 4.4, and the dielectric loss increased from 0.10 to 0.90 at 1 MHz for the dispersion of 6% CNT in PMMA. Scanning electron microscopy analysis showed that the internal particle structure and porosity had changed due to the presence of the CNTs in the PMMA. The dispersion of CNTs into the PMMA increased the maximum voltage of the polymer electrolytes. A breakdown voltage of 7.4 kV was attained with 6% CNTs in the polymer.

Simulation research of hole transport layer free CsPbI3/MAPbI3 heterojunction perovskite solar cells with an efficiency of 30.33 %

Constructing inorganic perovskite/organic-inorganic hybrid perovskite bilayer heterojunction perovskite solar cells (HPSC) could make far-reaching changes in solar cell power conversion efficiency (PCE). Herein, a carbon-based hole transport layer (HTL) free CsPbI3/MAPbI3 HPSC was designed and optimized by one-dimensional solar cell capacitance (SCAPS-1D) software. The film thickness, bulk defect density and doping concentration of each perovskite light absorption layer, and the interface defect density, the electrode work function and the operating temperature changes effect on the device performances were investigated. Under optimized conditions, the HPSC obtained the open circuit voltage (VOC) of 1.43 V, short circuit current density (JSC) of 23.39 mA cm−2, fill factor (FF) of 90.67 % and PCE of 30.33 %, which was much superior than the single junction perovskite solar cell due to the suited energy band structure.