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Interest in perovskite solar cell (PSC) research is increasing because PSC has a remarkable power conversion efficiency (PCE), which has notably risen to 28.3 %. However, commercialization of PSCs faces a significant obstacle due to their stability issues. This review article primarily focuses on several key aspects of PSCs, including different types of solar cells, their construction and operational mechanisms, efficiency, and overall stability. It explains the structure and functioning of PSCs, covering materials and components used for absorber layer, electron-transport layer, hole-transport layer, and electrodes. This review emphasized stability challenges associated with PSCs and discussed various factors and issues contributing to the degradation of these solar cells over time. It then provided a concise overview of different strategies and ongoing efforts taken to enhance the stability of PSCs. It also summarized various approaches used to improve their durability. In summary, this article offers a comprehensive exploration of PSCs, encompassing their construction, operation, improvement in efficiency, and obstacles related to their long-term stability. Furthermore, it addresses factors influencing PSC stability and outlines future challenges, focusing on prolonging their lifespan and enhancing stability for broader applications. Finally, this article has tackled various possible solutions to address the challenges encountered by the PSCs. [ABSTRACT FROM AUTHOR]

In the past decade, nanotechnology's rapid developments have created quite a lot of prospects for researchers and engineers to check up on. And nanofluids are important consequences of this progression. Nanofluids are created by suspending nanoparticles with average diameters below 100 nm in conventional heat transfer carriers such as water, oil, ethylene glycol, etc. Nanofluids are considered to offer substantial advantages over usual heat transfer fluids. When dispersed in a uniform way and suspended stably in the base fluids, a minimal amount of nanoparticles can significantly improve the thermal properties of host fluids. Present work attempts to address this challenge considering state-of-the-art advances in understanding, discussing, and mitigating problems about nanofluids' stability. Stable and highly conductive nanofluids are produced by generally, one-step and two-step production methods. Both approaches suffer from problems with the nanoparticles' agglomeration to be an important one. Thus, numerous numerical models and the principal physical phenomena affecting the stability (fundamental physical principles that govern the interparticle interactions, clustering and deposition kinetics, and colloidal stability theories) have been analyzed. Concerning the particles' dynamic motion, the significance of different forces in nanofluid in particulate flows such as drag, lift (Magnus and Saffman), Brownian, thermophoretic, Van der Waals, electrostatic double-layer forces are investigated. Furthermore, an overview of nanofluids' thermophysical properties, physical models, and heat transfer models is​ included in this work. In order to realize the unexpected discoveries and overcome classical models' limitations, several researchers have suggested new physical concepts and mechanisms, and they have created new models to enhance the transport properties. This review study includes numerous aspects of the nanofluids' science by investigating applications, thermal properties and giving critical chronological milestones about the nanofluids' evolution. Also, the present review discusses in detail various modeling and slip mechanisms for the heat transfer of nanofluids. Potential novel 2D materials as nanofluids have also been discussed and reported. A brief overview of the potential applications utilizing nanofluids has been reviewed, and future research gaps have been reported. Furthermore, recommendations were extracted regarding current scientific gaps and future research directions to cover the physical phenomenon, stability, thermophysical properties, overview of some applications, and the limitations hindering these nanofluids' deployment. The review is presumed to be valuable for scholars and researchers working in the area of numerical simulations of nanofluids and experimental aspects and help them understand the fundamental physical phenomena taking place during these numerical simulations and experiments and explore the potential of nanofluids both in academia and industry. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, ternary rGO-Fe 3 O 4 -TiO 2 nanocomposites was produced using a straightforward sol-gel technique. The nanofluids are synthesized using rGO-Fe 3 O 4 -TiO 2 hybrid nanoparticles suspended in ethylene glycol (EG). Ternary rGO-Fe 3 O 4 -TiO 2 nanocomposite (0.01–0.25 mass. %) were dispersed in EG acquiring stable nanofluids. The ternary rGO-Fe 3 O 4 -TiO 2 nanocomposite present in the colloidal phase has been categorized by FTIR, SEM, EDX, XRD, and Zeta potential. At varying temperatures between 25 and 60 °C, the thermal conductivity was explored. Experimental results show that the stability of all the studied rGO-Fe 3 O 4 -TiO 2 /EG nanofluid samples was above 52.04 mV. Enhancement in thermal conductivity for rGO-Fe 3 O 4 -TiO 2 /EG nanofluids significantly increases with mass concentration and temperature, with an enhancement of 13.3% at 60 °C for 0.25 wt%. The best R2 coefficient of determination estimated at 25 °C, 30 °C, 40 °C, 50 °C, and 60 °C was 95.6%, 98.2%, 95.4%, 97.6%, and 99.0%. Therefore, the investigated ternary hybrid nanofluid can be utilized for both heating and cooling applications with long term stability. Unlabelled Image • Novel ternary rGO-Fe 3 O 4 -TiO 2 nanocomposites was produced. • Stable nanofluids were prepared using Ternary rGO-Fe 3 O 4 -TiO 2 nanocomposite. • An enhancement of 11.5% at 40 °C for 0.25 wt%. was achieved. • Regression models for all the studied temperatures and mass concentration are provided. • A well-fitting is obtained between the experimental results and the regression model. [ABSTRACT FROM AUTHOR]

Advanced heat removal technologies are critical for high-performance automotive engines. The conventional fluids being used today are based on a mixture of distilled water (DW) and ethylene glycol (EG), which widens the operational temperature range but at the same time limits the heat removal. Therefore, the use of nanofluids for improving heat transfer performance has soared over the past few years. The problem is that most of the reports highlight the short-term heat transfer results which may not be true over time. In this paper, a suggested best practice for analyzing the usage of nanofluids in heat transfer applications is presented, specifically for an actual car radiator. This work investigates the use of aluminum oxide (Al 2 O 3) and titanium dioxide (TiO 2) nanoparticles dispersed in DW and EG at 50:50 volumetric proportions. The choice of these oxide-based nanofluids is motivated by their anti-corrosive properties that are usually not analyzed or discussed in most of the articles. Furthermore, the emphasis is given on the presentation of a comprehensive characterization of the nanofluids including thermophysical properties (size, density, viscosity, thermal conductivity, corrosive behavior) and long-term stability (zeta potential) which are essential for an end-user to have. The results showed a maximum enhancement of the thermal performance by 24.21% using Al 2 O 3 at a volume fraction of 0.3%. Friction factor and performance evaluation criterion (PEC) for the radiator experiments are calculated in order to determine the penalty in the pressure drop and to evaluate it properly. Finally, it is found that the values of PEC lie in the range of 1.03–1.31 which indicates significant flow enhancement. • A critical review on stability and application of nanofluids (NFs) in a radiator is presented. • The effect of surfactant concentration on stability is investigated. • Thermophysical properties of Al 2 O 3 –DW/EG and TiO 2 -DW/EG NFs are experimentally investigated. • Effect of NFs with respect to corrosion for the pipping system of the radiator is investigated. [ABSTRACT FROM AUTHOR]

Carbon-based nanofluids are viewed as promising thermal fluids for heat transfer applications. However, other properties, such as electrical conductivity and electrochemical behavior, are usually overlooked and rarely investigated despite their importance for the overall performance characterization of a given application. In this study, we synthesized PAN-based carbon nanofibers (CNF) by electrospinning, and characterized them using electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Thermoelectrical and electrochemical measurements were carried out on nanofluids. We found that, although CNF nanofluids exhibit good thermal and electrical properties with a negligible corrosive effect, the suspensions tend to sediment within a few days. However, acid treatment of CNF (F-CNF), which resulted in the shortening of the fibers and the appearance of surface-oxygenated species, made F-CNF-based nanofluids exhibit superior stability in water that extended for more than 90 days, with consistent and superior thermal and electrical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stability and thermophysical properties of Fe 3 O 4 coated MWCNT hybrid fluids studied. • Highest stability of –48 mv was achieved for 0.05% nanofluid concentration. • Thermal conductivity and viscosity improved to 28.33% and 50% for 0.3 vol%. • A robust MLP-ANN model with 99.38% accuracy was developed using experimental data. • Model's uncertainty was measured with Theil's U2 with high accuracy. Stability and thermophysical properties of water-based magnetite (Fe 3 O 4) material coated on multiwalled carbon nanotubes hybrid nanofluids was investigated. The in-situ growth approach was coupled with the chemical reduction method to make Fe 3 O 4 coated multiwalled carbon nanotubes, and X-ray diffraction, vibrating sample magnetometer, and scanning electron microscopy were used to validate these findings. The experiments were conducted for different particle volume loadings (0.05% to 0.3%). Highest stability value of –48 mv was achieved for ϕ = 0.05%. At, ϕ = 0.3% of nanofluid, the thermal conductivity was improved to 13.78%, and 28.33% at temperatures of 20 °C and 60 °C against water. Similarly, at ϕ = 0.3% of hybrid nanofluid, the viscosity has enhanced to 27.83%, and 50% at temperatures of 20 °C and 60 °C against water. Using the experimental data, sensitivity analysis was used to build Multi-Layer Perceptron Artificial Neural Networks (MLP-ANN) with appropriate topologies and training techniques. MLP-ANN was employed to establish the relationship between the inputs (temperature and mixture concentration) and the outputs (density, thermal conductivity, viscosity and, specific heat) for water-based magnetite (Fe 3 O 4) material coated on multiwalled carbon nanotubes hybrid nanofluids. The model performances were evaluated using the coefficient of correlation (0.9938–0.9999), coefficient of determination (0.9854–0.9996), root mean squared error (0.0072–0.2626), mean absolute percentage error (0.001%-2.09%), and Nash-Sutcliffe efficiency (0.9856–0.9999). The model's uncertainty was measured with Theil's U2 (0.035–0.267). The results revealed that the MLP-ANN could consistently emulate the experimental testing conditions proficiently, even for diverse temperatures and concentrations, with significant accuracy. [ABSTRACT FROM AUTHOR]

The main objective of the present study is to investigate the impact of nanofluid stabilization techniques (hybrid stabilization approach, i.e., a combination of different mechanical and chemical methods) on the stability and thermal conductivity of CeO 2 +MWCNT (80:20)/water based hybrid nanofluid. The nanofluid has been prepared by using the two-step method, and a broad range of ultrasonication time (30, 60, 90, 120, 150, and 180 min) has been used. Furthermore, different kinds of charged surfactants, two anionic (sodium dodecyl benzene sulfonate (SDBS), sodium dodecyl sulphate (SDS)), two cationic (cetyltrimethylammonium bromide (CTAB), distearyl dimethylammonium chloride (DDC)), and two polymers (gum Arabic (GA), PVP (polyvinyl pyrrolidone)) have been added to the base fluid with a different nanoparticle to surfactant mixing ratios (5:0, 4:1, 3:2, 2:3 and 1:4). The prepared samples were investigated at different pH values and different preparation days (15th, 30th, 45th,60th, and 90th day) to evaluate which surfactant and mixing ratios are sufficient to achieve a stable nanofluid for more than 90 days. The observed optimum volumetric mixing ratio of surfactant and CeO 2 +MWCNT nanoparticle, pH level and sonication time are around 3:2, 9.5, and 90 min, respectively, for which hybrid nanofluid yields maximum zeta potential value as an indicator of nanofluids long term stability. The results of zeta potential analysis indicated that CTAB surfactant shows the best impact up to the 30th day from preparation, after the 30th day, the SDBS surfactant shows the highest degree of stability of the hybrid nanofluid applying 3:2 mixing ratio and 90 min sonication. Results clearly showed that the nanofluid hybrid stabilization approach has a strong relation with thermal conductivity. The addition of higher amounts of surfactant (more than 3:2 mixing ratio) caused a small thermal conductivity reduction. Additionally, precise assessments of the surfactant effect on a hybrid nanofluid's surface tension have also been studied. Finally, a correlation to predict the experimental value of thermal conductivity has been proposed from the experimental data, which could be beneficial for various heat transfer applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigation of surfactants on stability, rheology and thermophysical properties of Water-EG based Al 2 O 3 -TiO 2 hybrid nanofluids. • Al 2 O 3 -TiO 2 hybrid nanofluids exhibit Newtonian behavior. • Surfactants increase the stability but compromised the thermal conductivity. • PVP incorporated nanofluids are stable for 60 days with zeta potential value of 55.6 mV. • Viscosity and thermal conductivity enhancement by PVP was 50% and 3.6% at 80 °C respectively. This study investigates the influence of eight distinct surfactants on the stability, rheological characteristics, and thermophysical properties of hybrid nanofluids (NFs) containing Aluminum oxide (Al 2 O 3) and Titanium dioxide (TiO 2) in a Water-Ethylene Glycol (EG) mixture (60:40). The objective and novelty of this research is to choose the best surfactant for long run applications in terms of stability, viscosity and thermal conductivity. The results reveal that polyvinylpyrrolidone (PVP) exhibited the highest stability among all surfactants, surpassing others in zeta potential and visual stability over 60 days. Additionally, all the nanofluids exhibited Newtonian behavior. Surfactant addition increased viscosity, with polyethylene glycol (PEG) showing the highest enhancement of 37.2 % at 30 °C. Thermal conductivity increased with temperature, maximum TC enhancement of 8.3 % at 80 °C was given by PEG and oleic acid (OA), but these surfactants were unstable to be used in any application. In conclusion, PVP emerged as the most suitable surfactant for Al 2 O 3 -TiO 2 hybrid nanofluids due to its exceptional stability, moderate viscosity, and TC enhancement. It enhanced the TC by 3.6% at 80°C and contributed 28.9% in viscosity increment at 30°C. This research contributes to the understanding of surfactant effects on nanofluid properties, particularly highlighting PVP's potential for long-term heat transfer applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A systematic review of stability and their influence on thermophysical properties of nanofluids is presented. • The review found that the volume fraction and particle size significantly affects thermophysical properties of nanofluids. • It provides precise instructions for synthesis, characterization, and assessment of nanofluid thermophysical characteristics. Nanofluid has been found exceptionally suitable in several heat transfer applications as a working fluid due to its excellent thermophysical properties. Enhancement in thermophysical properties of nanofluid is strongly influenced by its long-term stability. Several parameters such as base fluid type, nanoparticle type, surfactant type, nanoparticle size and morphology, preparation method, and pH of the synthesized fluid affect nanofluid stability. This article addresses a detailed review of synthesis techniques, stability evaluation, enhancement techniques, and parametric effect on the stability of nanofluid. The article also includes a systematic review of various thermophysical properties of mono, hybrid, and ternary nanofluid and the influence of several parameters on thermophysical properties of nanofluid. Volume fraction and particle size significantly enhanced several thermophysical properties such as thermal conductivity and viscosity. However, results reported by researchers were inconsistent and conflicting, which needs further investigation. The article also reviews nanofluid suitability in various heat transfer applications such as solar collectors, electronic cooling, refrigeration systems, solar distillation system, two-phase heat transfer, and heat exchangers. Nanofluids were found suitable and demonstrated improvement in the performance of the system. A review of the economic analysis of nanofluid has also been included in the article. Stable synthesized nanofluid demonstrates its economic suitability, which ultimately translates nanofluid research from lab scale to commercial utilization. Researchers could benefit from the explicit guidelines provided by the current study for the synthesis, characterization, and assessment of the thermophysical properties of mono and hybrid nanofluids. [ABSTRACT FROM AUTHOR]

• Super stable copper oxide/DES nanofluids were achieved. • One-step preparation protocol from homogeneous DES Cu(OH) 2 solution was realized; • Thermophysic and photothermal characteristics of the nanofluids were comprehensively studied. Nanofluid has gained vast attention as a novel heat transfer working fluid owing to its superiority in thermal conductivity and rheological properties. Meanwhile, the liquid range and the stability of nanofluids are of great significance since it dominates the utilization scope of a working fluid. In this work, with the aim at solving the poor stability associated with short liquid range of traditional nanofluids, a novel "one-step" preparation protocol was developed using Cu(OH) 2 as a precursor and deep eutectic solvents (DESs) as dispersing medium. The as-prepared nanofluid bears an extraordinary static stability that can be kept for at least two months without observation of any sedimentation thanks to the in-situ formed Cu 2 O nanoparticle in DESs under a microwave irradiation condition and wide liquid range attributed to the low saturated pressure of DESs. Structural analysis, such as SEM, TEM, XRD, XPS and FTIR analysis, and thermophysical properties of the nanofluids were subject to a comprehensive study. Thermal conductivity analysis indicated that the presence of Cu 2 O nanoparticle slightly impacts the thermal conductivity when the mass fraction of the nanoparticle is small. Notably, this DESs based nanofluid features promising photothermal conversion that can reach 83.74% with the addition of 0.1 wt % Cu 2 O nanoparticle. This study provides an important avenue for the preparation of nanofluids with high static stability. [ABSTRACT FROM AUTHOR]

The hybrid nanofluids were used as absorber fluids in solar energy applications, which could further increase the efficiency of solar devices. The use of nanofluids in solar devices with the laminar and turbulent flow has received much attention. Presently, the effect of temperature and concentration on thermal conductivity and viscosity of fly ash-copper (80:20% by volume) hybrid nanofluid is investigated. The thermal conductivity and viscosity measurements were carried in the temperature range of 30–60 °C for a concentration range of 0–4.0 vol%. The nanoparticles and nanofluids were characterized by XRF, XRD, SEM, TEM, zeta potential, and DLS techniques. The maximum augmentation in the hybrid nanofluid's dynamic viscosity and thermal conductivity at a concentration of 4 vol% is 45.18% and 49.8%, respectively, at 30 and 60 °C. Correlations to estimate the hybrid nanofluid's dynamic viscosity and thermal conductivity have been proposed considering the results obtained from the present study. A radial basis function-based neural network is used to model nanofluids' effective thermal conductivity and relative viscosity. The outcomes of the experiments were used to calculate the Mouromtseff number and heat transfer efficiency for solar energy applications. • HyNF shows Newtonian behavior in the studied range. • The maximum augmentation in viscosity is 45.2%. • The highest amplification in thermal conductivity is 49.8%. • Radial basis function based neural network was used. [ABSTRACT FROM AUTHOR]