Utilization Of Solar Spectrum Research Articles

Enhanced Light Absorption and Photo-Generated Charge Separation Efficiency for Boosting Photocatalytic H2 Evolution through TiO2 Quantum Dots with N-Doping and Concomitant Oxygen Vacancy.

Low-range light absorption and rapid recombination of photo-generated charge carriers have prevented the occurrence of effective and applicable photocatalysis for decades. Quantum dots (QDs) offer a solution due to their size-controlled photon properties and charge separation capabilities. Herein, well-dispersed interstitial nitrogen-doped TiO2 QDs with stable oxygen vacancies (N-TiO2-x-VO) are fabricated by using a low-temperature, annealing-assisted hydrothermal method. Remarkably, electrostatic repulsion prevented aggregation arising from negative charges accumulated in situ on the surface of N-TiO2-x-VO, enabling complete solar spectrum utilization (200-800 nm) with a 2.5 eV bandgap. Enhanced UV-vis photocatalytic H2 evolution rate (HER) reached2757µmol g-1 h-1, 41.6 times higher than commercial TiO2 (66µmol g-1 h-1). Strikingly, under visible light, HER rate was 189µmol g-1 h-1. Experimental and simulated studies of mechanisms reveal that VO can serve as an electron reservoir of photo-generated charge carriers on N-doped active sites, and consequently, enhance the separation rate of exciton pairs. Moreover, the negative free energy (-0.35 V) indicates more favorable thermodynamics for HER as compared with bulk TiO2 (0.66 V). This research work paves a new way of developing efficient photocatalytic strategies of HER that are applicable in the sustainable carbon-zero energy supply.

Cascade utilization of full spectrum solar energy for achieving simultaneous hydrogen production and all-day thermoelectric conversion

Solar-driven photocatalytic water/seawater splitting holds great potential for green hydrogen production. However, the practical application is hindered by the relatively low conversion efficiency resulting from the inadequate utilization of solar spectrum with significant waste in the form of heat. Moreover, current equipment struggles to maintain all-day operation subjected to the lack of light during nighttime. Herein, a novel hybrid system integrating photothermal catalytic (PTC) reactor, thermoelectric generator (TEG), and phase change materials (PCM) was proposed and designed (named as PTC-TEG-PCM) to address these challenges and enable simultaneous overall seawater splitting and 24-hour power generation. The PTC system effectively maintains in an optimal temperature range to maximize photothermal-assisted photocatalytic hydrogen production. The TEG component recycles the low-grade waste heat for power generation, complementing the shortcoming of photocatalytic conversion and achieving cascade utilization of full-spectrum solar energy. Furthermore, exceptional thermal storage capability of PCM allow for the conversion of released heat into electricity during nighttime, contributing significantly to the overall power output and enabling PTC-TEG-PCM to operate for more than 12 h under the actual condition. Compared to traditional PTC system, the overall energy conversion efficiency of the PTC-TEG-PCM system can be increased by ∼500%, while maintaining the solar-to-hydrogen efficiency. The advancement of this novel system demonstrated that recycling waste heat from the PTC system and utilizing heat absorption/release capability of PCM for thermoelectric application are effective strategies to improve solar energy conversion. With flexible parameter designing, PTC-TEG-PCM can be applied in various scenarios, offering high efficiency, stability, and sustainability.

Construction of TiO2@Cu2O-CuS heterostructures integrating RGO for enhanced full-spectrum photocatalytic degradation of organic pollutants

This study presents the development and optimization of TiO2@Cu2O-CuS heterostructures, enhanced with reduced graphene oxide (RGO), for efficient photocatalytic degradation of organic pollutants, focusing on imidacloprid. Two configurations, TiO2/RGO/Cu2O-CuS and Cu2O-CuS/RGO/TiO2, are explored to highlight the impact of material layering on photocatalytic efficiency. The strategic integration of RGO optimizes charge transfer, crucial for photocatalysis. Comprehensive characterization techniques, such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and Nitrogen adsorption-desorption isotherms, provide insights into the crystalline structure, morphology, surface chemistry, and textural properties of the heterostructures. The TiO2/RGO/Cu2O-CuS configuration significantly outperforms its counterpart in photocatalytic activity under full-spectrum (UV–VIS–IR) illumination, due to improved charge carrier dynamics and synergistic interactions between the composite materials. Remarkably, the TiO2/RGO/Cu2O-CuS assembly achieved over 95 % degradation of imidacloprid under simulated solar irradiation, marking a breakthrough in solar spectrum utilization for photocatalysis and exhibits promising recyclability, maintaining its high photocatalytic efficiency even after multiple degradation cycles, highlighting its potential for sustainable pollutant removal applications. Additionally, this configuration demonstrates a twofold increase in degradation efficiency compared to separate UV and VIS irradiations, emphasizing its rapid pollutant removal capability. This research underscores the critical role of material layer sequencing in developing high-efficiency photocatalytic systems and marks a significant advancement in environmental remediation technologies that harness renewable energy sources.

MXene/Ag3PO4 modified PVDF composite membranes for efficient interfacial evaporation and photodegradation

Solar-powered interface evaporation is considered a promising technology to obtain freshwater from non-potable water by using sustainable solar energy. However, research on combining the photocatalytic effect with solar interfacial evaporation technology to go for photothermal conversion materials with full solar spectrum utilization for photothermal and photodegradation capabilities is still scarce. Due to the unique optical properties of MXene, a novel MXene/Ag3PO4-based membrane with synergistic photothermal and photocatalytic effects was developed from the perspective of practical applications such as water purification, photodegradation of organic dyes and antibacterial properties. In this paper, polyvinylidene fluoride (PVDF) and carbon black (CB) were used as the substrate, calcium carbonate (CaCO3) and hydrochloric acid (HCl) were selected as the pore-forming agent for hydrophilic modification, and MXene/Ag3PO4 serves as the photocatalyst. The prepared composite polyvinylidene fluoride membrane (PCC-MXene/Ag3PO4) with Schottky junction, possesses a rich pore structure, abundant water molecule transport channels, high light absorption ability, and low thermal conductivity, which lead to a good performance in solar interface evaporation, photodegradation and antibacterial. The superhydrophobicity and floatability of the nanosponges in water enable them to continuously pump water, which greatly promotes the dissolution of salt accumulation. With the help of porous nanosponges, PCC-MXene/Ag3PO4 exhibits excellent evaporation stability and salt resistance under 1 kW m−2 solar irradiation, as well as photodegradation of organic dyes. In addition, the PCC-MXene/Ag3PO4 membrane has the properties of self-buoyancy, electrical conductivity, and superior flexibility. Therefore, considering the simple preparation method and fine performances, the PCC-MXene/Ag3PO4 mixed membrane has great application potential in the study of interface evaporation, photodegradation of organic dyes, and antibacterial properties.

Unveiling the Potential of Two-Terminal Perovskite/Organic Tandem Solar Cells: Mechanisms, Status, and Challenges.

Perovskite/organic tandem solar cells (PO-TSCs) demonstrate exceptional suitability for emerging applications such as building-integrated photovoltaics, wearable devices, and greenhouse farming. By leveraging the distinctive attributes of perovskite and organic materials, which encompass expanded solar spectrum utilization, chemically benign solubility, and soft nature, PO-TSCs position themselves as ideal candidates for high-performance semi-transparent photovoltaics (ST-PVs). Despite these advantages, their development significantly lags behind other perovskite-based counterparts, such as perovskite/perovskite, perovskite/silicon, and perovskite/Cu(In, Ga)Se2. To address existing challenges and unlock the full potential of PO-TSCs, an exploration of the fundamental mechanisms governing tandem photovoltaic devices is embarked. Delving into critical aspects such as charge generation/separation, energy level alignment, and material choices becomes pivotal for optimizing PO-TSC performance. The investigation of monolithic two-terminal PO-TSCs offers insights into achievements and barriers, recognizing the competitive landscape with other TSC counterparts. Further scrutiny of perovskite absorbers and organic absorbers in TSCs reveals strategies aimed at enhancing stability and efficiency. The discussion extends to interconnection layers, elucidating their role in optimizing light transmission and balancing carrier recombination. In conclusion, a compelling outlook on the dynamic landscape of PO-TSCs is presented, highlighting the remarkable efficiency progression and signaling their potential to revolutionize solar energy harvesting technologies.

Near‐Infrared Active Tri‐nanohybrid for Enhanced Energy Harvesting

AbstractEfficient energy harvesting through full solar spectrum utilization has been considered a promising solution to world energy and environmental issues. In this direction, lead sulphide (PbS) quantum dot (QD) based hybrid materials find greater application due to their near‐infrared (NIR) active photo response. Slower charge injection and inefficient charge separation limit photoactive response of such NIR active low band gap semiconductor like PbS QDs. Moreover, constructing dual charge transfer pathways in a PbS QDs based nanocomposite through the formation of hybrids with suitable materials can be advantageous in suppressing the charge recombination. In this work, we have synthesized a nanocomposite after decorating the PbS‐QDs with semiconducting TiO2 nanoparticles modified with multiwall carbon nanotubes (MWCNT) and thus forming the tri‐hybrid (PbS‐TiO2‐MWCNT) nanocomposites. The enhanced photo‐activities of the tri‐hybrid, as compared to di‐hybrids like PbS‐TiO2, PbS‐MWCNT were confirmed by the steady state, time‐resolved photoluminescence (TRPL) measurements and reactive oxygen species (ROS) generation measurements. Higher ROS generation in the tri‐hybrid has been correlated with a faster interfacial electron transfer due to the dual charge injection pathway of PbS QD to TiO2 and MWCNT. The enhanced activity of the trio‐hybrid has also been analyzed from the first principal calculations in light of an efficient interfacial electron transfer as a result of the dual charge injection pathway. The photoelectrochemical water‐spilling response of the photoanodes in terms of photocurrent density, electrochemical impedance, and Mott–Schottky measurements on PbS‐TiO2 and PbS‐TiO2‐MWCNT photoanodes reveal that a combination of MWCNT and TiO2 exhibits an increase in electrical double layer capacitance, decrease in series resistance and enhancement of carrier density with NIR illumination at the heterojunction. Overall, all the dynamical studies at the interface of the trihybrid‐based photoanodes demonstrate its potential of utilization as a futuristic NIR‐ active photoelectrochemical water‐splitting material.

Improved Performance of Lead‐Free Perovskite Solar Cells Based on Multi‐Absorber MASnI3/CsGeI3 Heterojunction by Device Simulation

AbstractLead‐free perovskite solar cell (PSC) is the direction of future development of PSCs due to its reduced toxicity. However, the power conversion efficiency (PCE) of the lead‐free PSCs is still lagging behind their lead‐based counterparts, which hinders their further application. Multi‐absorber approach can effectively overcome this problem as it allows the maximum utilization of solar spectrum. Therefore, in this study a novel lead‐free MASnI3/CsGeI3 heterojunction structure is proposed to boost the performance of PSCs based on single CsGeI3 absorption layer. The critical device parameters including absorber thickness, defect density, doping concentration, and back contact work function are studied and optimized using the numerical software SCAPS‐1D. Under optimized conditions, PSCs based on Sn/Ge bilayer structure yield a considerable PCE of 16.15%, significantly higher than the single CsGeI3 based PSCs (optimized PCE of 7.43%) with higher thermal stability. The simulation results indicate a huge potential of the proposed multi‐absorber heterojunction structure for highly efficient lead‐free PSCs, which will contribute to achieving clean and sustainable energy in the future.

Designing energetic landscape in the multi-bandgap lead sulphide colloidal quantum dots ensemble for efficient solar spectrum utilization

The distinctive nature of the solar spectrum in the near and shortwave infrared region demands the appropriate design of the active materials for efficient infrared photon absorption in a solar cell. Colloidal quantum dots (CQDs) based on lead sulphide (PbS) showed significant absorption in the near and shortwave infrared region through bandgap tuning. Despite their high absorption coefficient, PbS CQDs show a strong excitonic absorption peak, which cannot cover a significant portion of the solar spectrum in the near or shortwave infrared region. Mixing CQDs with different bandgaps can lead to better coverage of the solar spectrum and, hence, better photon absorption. In this work, we have estimated the ideal PbS CQD-based multi-bandgap ensemble combination and active material design strategy for optimum infrared photon absorption. In addition, we have investigated in detail the crucial factors that decide the performance of solar cells based on multi-bandgap CQDs. The simulation shows that careful optimization of the energetic landscape of the ensemble, along with the charge carrier mobility, can improve the efficiency up to 16.48 % under the AM 1.5 G spectrum. The optimized infrared photovoltaic performance with a perovskite filter can reach up to 9.29 %.

Enhancing solar spectrum utilization in photosynthesis: exploring exciton and site energy shifts as key mechanisms

Photosynthesis is a critical process that harnesses solar energy to sustain life across Earth's intricate ecosystems. Central to this phenomenon is nuanced adaptation to a spectrum spanning approximately from 300 nm to nearly 1100 nm of solar irradiation, a trait enabling plants, algae, and phototrophic bacteria to flourish in their respective ecological niches. While the Sun’s thermal radiance and the Earth’s atmospheric translucence naturally constrain the ultraviolet extent of this range, a comprehension of how to optimize the utilization of near-infrared light has remained an enduring pursuit. This study unveils the remarkable capacity of the bacteriochlorophyll b-containing purple photosynthetic bacterium Blastochloris viridis to harness solar energy at extreme long wavelengths, a property attributed to a synergistic interplay of exciton and site energy shift mechanisms. Understanding the unique native adaptation mechanisms offers promising prospects for advancing sustainable energy technologies of solar energy conversion.

A synergistic approach in designing InP/ZnS quantum dot based CIGS solar cell

This research work investigates the implementation of non-toxic InP/ZnS quantum dot (QDs) buffer layer in solar cell. Due to its nontoxic behaviour, it is a better replacement of commonly used CdS buffer layer. InP/ZnS quantum dots buffer layer enhances light absorption, leading to a broader spectral response and improved power conversion efficiency. Graded CIGS (CuIn1-xGaxSe2) is used as absorber layer in this study for better utilization of solar spectrum. The combined utilization of an InP/ZnS QD buffer layer and a graded absorber layer results in a synergistic enhancement of the cell's performance. Further optimization of CIGS layers is achieved by varying the gallium content (x) in the Cu(In1−xGax)Se2. For the gallium content (x) in the range of 0.20 to 0.15, maximum efficiency is achieved which is 31.20 %. Numerical modeling is employed in this study to analyze how variations in thickness, doping concentration, and defect density impact the solar cell performances.

Towards a luminescent solar concentrator with ultra-broadband absorption and spectral conversion for optimizing photovoltaic solar cell response: “The photonic cannon shot”

Solar energy harvesting is largely limited by the spectral sensitivity of the employed photovoltaic solar cell, since typically the full potential of each photon of the whole solar spectrum is not efficiently used in the generation of electricity. Therefore, increasing the overall solar spectrum utilization is of crucial interest and stands up as a frontier-of-research approach in the photovoltaic sector. Here we present an innovative ultra-broadband absorption and multiple spectral conversion approach, by means of rare-earth doped materials together with organic dyes embedded in a luminescent solar concentrator. The combination of different luminescent materials is a key factor for improving energy harvesting over the whole solar spectrum. At the same time, a simultaneously combined effect of up-conversion and down-shifting of light is aimed to optimal spectral matching with amorphous silicon solar cells response. Thus, UV–visible photons coming from the incoming sunlight, together with UV–visible up-converted photons coming from near-infrared radiation, can be all shifted to the yellow-orange-red part of the spectrum. To the best of our knowledge, this represents the first reported proof-of-concept using LSCs with up-conversion and down-shifting photonic processes working together and sequentially.

Construction of Z-Scheme In2S3-TiO2 for CO2 Reduction under Concentrated Natural Sunlight

Producing chemical fuels from sunlight enables a sustainable way for energy consumption. Among various solar fuel generation approaches, photocatalytic CO2 reduction has the advantages of simple structure, mild reaction condition, directly reducing carbon emissions, etc. However, most of the current photocatalytic systems can only absorb the UV-visible spectrum of solar light. Therefore, finding a way to utilize infrared light in the photocatalytic system has attracted more and more attention. Here, a Z-scheme In2S3-TiO2 was constructed for CO2 reduction under concentrated natural sunlight. The infrared light was used to create a high-temperature environment for photocatalytic reactions. The evolution rates of H2, CO, and C2H5OH reached 262.2, 73.9, and 27.56 µmol·h-1·g-1, respectively, with an overall solar to fuels efficiency of 0.002%. This work provides a composite photocatalyst towards the utilization of full solar light spectrum, and could promote the research on photocatalytic CO2 reduction.

Multi-scale multi-physic coupled investigation on the matching and trade-off of conversion and storage of optical, thermal, electrical, and chemical energy in a hybrid system based on a novel full solar spectrum utilization strategy

In order to achieve a reasonable utilization of the full solar spectrum at low-cost, a photovoltaic/thermoelectric/electrolysis (PTE) hybrid system based on a novel full solar spectrum utilization strategy is proposed. The PTE mainly consist of a thermal collector with the spectrally selectively absorption fluid (water), a photovoltaic-thermoelectric (PV–TE) component and a water electrolysis component. Based the structure of the PTE, the full solar spectrum energy can be reasonably and efficiently allocated and utilized. For the complicated coupling physical process in PTE hybrid system, an integrated multi-scale multi-physic theoretical model is developed to optimize and investigate the PTE hybrid system. After the analyses on the multis-scale multi-physic effect of the air insulation layer between the thermal collector and the PV–TE component, it is found that removing air insulation layer leads to the less reflection loss and parasitic absorption, and more the maximum achievable photo current density and the internal heat source for TE component. Moreover, not only does the PV–TE component without the air insulation layer have higher efficiency (27.03%), but the concentration corresponding to the maximum efficiency increase to 31 from 3, which means more output power. By matching the structure and energy between components, the efficiency of the PTE hybrid system can be further improved, while the efficiency and energy storage of the PTE hybrid system can be adjusted according to the demand. Compared to single PV system, the efficiency of the PTE hybrid system has been increased by 15.38% at the concentration of 20, and this difference increases with the concentration. Moreover, the PTE hybrid system can simultaneously generate 200 W/m2 of hydrogen energy at the concentration of 20. In summary, the PTE hybrid system not only offers better performance (generation and storage), but also better integration, providing a guiding idea for the full solar spectrum utilization. Moreover, the multi-scale multi-physic coupled model also provides precise theoretical guidance for the optimization and design.

Establishment of a novel system for photothermal removal of ampicillin under near-infrared irradiation: Persulfate activation, mechanism, pathways and bio-toxicology

One of the most effective ways to address the problems of low solar spectrum utilization in photocatalysis and the high cost of persulfate activation technology is to create a cost-effective synergistic photothermal persulfate system. In this work, a brand-new composite catalyst called ZnFe2O4/Fe3O4@MWCNTs (ZFC) was developed to activate PDS (K2S2O8) from the aforementioned basis. ZFC's surface temperature could unbelievably reach 120.6 °C in 150 s together with the degrading synergistic system solution temperature could reach 48 °C under near-infrared light (NIR) in 30 min, thus accelerating the ZFC/PDS decolorization rate for reactive blue KN-R (150 mg/L) to 95% in 60 min. Furthermore, the ZFC's ferromagnetism bore it with good cycling performance, allowing it to maintain an 85% decolorization rate even after 5 cycles with OH·, SO4-·, 1O2, and O2–· dominating the degrading process. In the meantime, the DFT calculations of the kinetic constants for the entire process of S2O82- adsorption on Fe3O4 in dye degradation solution were in agreement with the outcomes of the experimental pseudo-first-order kinetic fitting. By analyzing the particular degradation route of ampicillin (50 mg/L) and the possible environmental impact of the intermediate using LC-MS and the toxicological analysis software (T.E.S.T.), respectively, it was shown that this system might function as an environmentally friendly method for removing antibiotics. This work may provide some productive research lines for the creation of a photothermal persulfate synergistic system and suggest fresh approaches to water treatment technology.

Combined effects of Pt nanoparticles and oxygen vacancies to promote photothermal catalytic degradation of toluene

Pt/Mn-TiO2 photothermal catalysts with abundant oxygen vacancies are prepared by loading Pt onto a composite of MnOx and TiO2 using MIL-125 as precursor (abbreviated as Mn-TiO2) and subsequent hydrogen reduction treatment. Under light irradiation with intensity of 625 mW/cm2, the optimal 0.65Pt/Mn-TiO2 catalyst can achieve toluene conversion of 90.4 % and CO2 yield of 85.6 %, respectively, and maintain stable activity for at least 30 h in the presence of coke and water. The introduction of Pt nanoparticles improves the utilization of solar spectrum and facilitates the generation of more oxygen vacancies. The comparative experiments of photothermal catalysis and thermal catalysis further verify that light not only acts as a heat source but also enhances catalytic reaction through photocatalysis and photoactivation of lattice oxygen. In the follow-up work, catalytic oxidation under natural sunlight is performed on 0.65Pt/Mn-TiO2 to reach 75.0 % of toluene conversion, displaying a good practical application potential.

Insights into morphology-dependent Au/TiO2catalyst in glycerol aqueous solutions towards photothermal reforming hydrogen production

Probing the effect of spatial morphology of catalyst on its photothermal catalytic performance is crucial for solar-driven renewable catalytic reforming of hydrogen production. In this study, Au nanoparticles loaded on various morphologies of TiO2 nanoparticles were synthesized and characterized. The experimental results indicated that decorating TiO2 with Au nanoparticles could dramatically increase its photocatalytic activities by 20–40 times. The photothermal conversion efficiency of Au/TiO2 (12.74%–25.54%) was higher than those of TiO2 due to the introduction of LSPR of Au nanoparticles could effectively improve the utilization of solar spectrum. Titania nanoflower (TNF) nanoparticles with high light absorption capacity, better colloidal dispersion stability, porous properties and narrow band gap represented the highest H2 productivity (144.13 μmol·g−1·h−1). The coarse surface structure was also conducive to the dispersion of gold particles on the surface of the carrier and the growth rate of Au/TNF hydrogen production (40 times) which was higher than that of other morphology within 2 h. The results of glycerol photothermal hydrogen generation highlighted the effect of temperature on colloidal dispersion stability and hydrogen production capability of nanoparticle suspension. It demonstrated that the photothermal effect aroused a temperature rise that would deteriorate the dispersion stability of the suspension although a local entropy increase in the catalyst nanoparticles might occur. At the same time, the temperature rise caused by the photothermal effect efficiently produces hydrogen in the reaction temperature range. Therefore, an ideal temperature setting for maximal hydrogen generation could be validated and improved the photothermal synergistic impact on biomass-reformed hydrogen generation.

Enhanced interfacial charge transfer and photothermal effect via in-situ construction of atom co-sharing Bi plasmonic/Bi4O5Br2 nanosheet heterojunction towards improved full-spectrum photocatalysis

Constructing a plasmonic heterojunction photocatalyst is a prospective approach to improve full-spectrum photocatalytic performance. However, low interfacial charge transfer efficiency due to lattice mismatch severely limits its photocatalytic performance. Herein, a Bi atom co-sharing Bi/Bi4O5Br2 plasmonic heterojunctions were fabricated via in-situ reduction. Experimental characterizations and theoretical calculations demonstrate that the co-sharing Bi atom enables intimate contact in the heterointerface, significantly promoting interfacial charge transfer and separation. In addition, Bi metal's surface plasmon resonance effect extends the photoresponse to the near-infrared region and enhances the photothermal performances, significantly improving solar energy's utilization efficiency. By these prominent features, the optimized Bi/Bi4O5Br2 heterojunctions show that the photocatalytic degradation ratio of BPA reaches 100 % within 40 min under full-spectrum irradiation, which is about three times higher than that of Bi4O5Br2. Moreover, the photocatalytic efficiency was significantly increased by 7.5 times with the increase in temperature under NIR light irradiation due to the photothermal effect. This work offers new insights into the rational design of low-cost, highly efficient, and stable Bi-based plasmonic heterojunction photocatalysts for full solar spectrum utilization by integrating plasmonic nanostructures and photothermal effect.

Thermal management of a mono-crystalline PV/T system using gold plasmonic nanofluid based optical filter

Solar energy can fulfill most of the world's electrical and thermal energy demands. The utilization of nanofluids in solar Photovoltaic/Thermal (PV/T) systems, to enhance the overall system performance using passive and active methods, have been studied explicitly in the last few years. More recently, nanofluid-based optical filters are integrated in decoupled fashion with Photovoltaic (PV) systems for the effective utilization of solar spectrum i.e. below and beyond the band-gap of PV cells. For the work presented here, we compared thermal performance of Au nanofluid-based optical filter (at 0.0002 wt%)over base fluid water on a 50 W mono-crystalline PV module under real outdoor conditions. The study results showed that in comparison to DI water, Au lowers the average surface temperature of the PV module, and hence better overall system efficiency compared to water as an optical filter. The overall efficiency of PV/T system was observed about 42%, 37% and 14% with Au nanofluid optical filter, de-ionized water filter, and bare PV module, respectively. This study revealed that the overall efficiency of the PV module with Au nanofluid as the optical filter can be enhanced.

MODEL DEVELOPMENT AND PERFORMANCE IMPROVEMENT OF A PHOTOVOLTAIC-THERMOELECTRIC SYSTEM BY INTEGRATING AND OPTIMIZING PHASE CHANGE MATERIALS

Integrating phase change materials (PCMs) with concentrated photovoltaic-thermoelectric (PV-TE) systems can effectively control the interface temperature between PV and TE components and improve the full solar-spectrum utilization efficiency. However, since the structure of photovoltaic-phase change material-thermoelectric (PV-PCM-TE) systems is complex and the temperatures among the components are coupled and affect each other, the photo-thermal-electric conversion characteristics under the actual physical properties need to be analyzed by a more detailed model, and the suitable operating conditions for PV-PCM-TE systems remain clear. There is still a lack of the method for improving the system performance. Therefore, a three-dimensional transient model is established herein by combining the Monte Carlo ray-tracing method and finite volume method to simulate the complex energy conversion processes of the PV-PCM-TE system. Based on this, performances of PV-PCM-TE, PV-TE, and PV systems are compared under different operating conditions, and the applicable conditions for PV-PCM-TE systems are analyzed. Then effects of key parameters of the phase change module are investigated. In the end, to further improve the system performance, a partition screening method of PCM is proposed considering the nonuniform solar radiation on photovoltaic surfaces, and the selection and layout area of PCMs are optimized. The results present that the applicable operating conditions are low concentration ratio (< 20) and low heat transfer coefficient (< 20 W·m<sup>-2</sup>·K<sup>-1</sup>). In terms of structural parameters, the system power generation is most significantly affected by the width. In terms of PCM physical properties, it is most affected by the PCM density, followed by latent heat. For different concentration ratios, there are different optimal melting points to achieve the highest power generation. The proposed PCM partition screening method can efficaciously control PV-TE interface temperature, and reduce photovoltaic cells' temperature by 47°C. The system efficiency can be increased by 4.8% and 4.2% after the optimization compared with that of the single PV cell and the traditional PV-TE system, respectively.

TiO2/CdS/CdSe quantum dots co-sensitized solar cell with the staggered-gap (type-II) heterojunctions for the enhanced photovoltaic performance

The effect of co-sensitization and ZnS passivation on the photovoltaic performance of CdS quantum dot sensitized solar cells (QDSSCs) were investigated. The deposition of CdS, CdSe quantum dots (QD) and ZnS passivation on TiO2 photoanode was carried out by successive ionic layer adsorption and reaction (SILAR) method. CdS/CdSe co-sensitization developed two staggered type-II heterojunctions at TiO2/CdS and CdS/CdSe interfaces and resulted a cascade energy band structure. This suitable band alignment facilitated the double charge transfer mechanism at each heterojunction and transported the electrons easily into the photoanode. The narrow bandgap sensitizers CdS and CdSe significantly improved the potential utilization of solar spectrum with more charge carrier generation. ZnS passivation on QD surface suppressed electrode/electrolyte interfacial charge recombination and facilitated more electron injection from QDs into TiO2 photoanode. The EDAX elemental mapping results inferred that CdS, CdSe and ZnS have efficiently covered the TiO2 surface. TiO2/CdS and CdS/CdSe interfaces and the amorphous nature of ZnS could be verified with HRTEM images. Hence, the co-sensitization and surface passivation played a significant role to enhance the PCE of CdS QDSSC from 1.9% to 4.05%.