Next-generation solar power conversion systems in concentrating solar power (CSP) applications require high-temperature advanced fluids in the range of 600–800°C. Current commercial CSP plants use ...molten nitrate salt mixtures as the heat transfer fluid and the thermal energy storage (TES) media while operating with multiple hours of energy capacity and at temperatures lower than 565°C. At higher temperatures, the nitrates cannot be used because they decompose. Molten chloride salts are candidates for CSP applications because of their high decomposition temperatures and good thermal properties; but they can be corrosive to common alloys used in vessels, heat exchangers, and piping at these elevated temperatures. In this article, we present the results of the corrosion evaluations of several alloys in eutectic 34.42wt% NaCl – 65.58wt% LiCl at 650–700°C in nitrogen atmosphere. Electrochemical evaluations were performed using open-circuit potential followed by a potentiodynamic polarization sweep. Corrosion rates were determined using Tafel slopes and Faraday's law. A temperature increase of as little as 50°C more than doubled the corrosion rate of AISI stainless steel 310 and Incoloy 800H compared to the initial 650°C test. These alloys exhibited localized corrosion. Inconel 625 was the most corrosion-resistant alloy with a corrosion rate of 2.80±0.38mm/year. For TES applications, corrosion rates with magnitudes of a few millimeters per year are not acceptable because of economic considerations. Additionally, localized corrosion (intergranular or pitting) can be catastrophic. Thus, corrosion-mitigation approaches are required for advanced CSP plants to be commercially viable.
•The 50°C temperature increase, from the initial 650°C test, more than doubled the corrosion rate of SS310 and In800H.•IN625 was the most corrosion-resistant alloy with a corrosion rate of 2.80±0.38 mm/year at 650°C.•SS347, with the lowest Ni content of 9.62 wt%, has the highest corrosion rate of 7.49±0.32 mm/year at 650°C.•Cr and Fe were preferentially corroded from SS310, In800H, and IN625.
Perovskite solar cells (PSCs) with an inverted structure (often referred to as the p-i-n architecture) are attractive for future commercialization owing to their easily scalable fabrication, reliable ...operation and compatibility with a wide range of perovskite-based tandem device architectures
. However, the power conversion efficiency (PCE) of p-i-n PSCs falls behind that of n-i-p (or normal) structure counterparts
. This large performance gap could undermine efforts to adopt p-i-n architectures, despite their other advantages. Given the remarkable advances in perovskite bulk materials optimization over the past decade, interface engineering has become the most important strategy to push PSC performance to its limit
. Here we report a reactive surface engineering approach based on a simple post-growth treatment of 3-(aminomethyl)pyridine (3-APy) on top of a perovskite thin film. First, the 3-APy molecule selectively reacts with surface formamidinium ions, reducing perovskite surface roughness and surface potential fluctuations associated with surface steps and terraces. Second, the reaction product on the perovskite surface decreases the formation energy of charged iodine vacancies, leading to effective n-type doping with a reduced work function in the surface region. With this reactive surface engineering, the resulting p-i-n PSCs obtained a PCE of over 25 per cent, along with retaining 87 per cent of the initial PCE after over 2,400 hours of 1-sun operation at about 55 degrees Celsius in air.
The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br-I) mixed-halide perovskite (with Br greater than 20%) is critical to create ...tandem solar cells. However, issues with Br-I phase segregation under solar cell operational conditions (such as light and heat) limit the device voltage and operational stability. This challenge is often exacerbated by the ready defect formation associated with the rapid crystallization of Br-rich perovskite chemistry with antisolvent processes. We combined the rapid Br crystallization with a gentle gas-quench method to prepare highly textured columnar 1.75-electron volt Br-I mixed WBG perovskite films with reduced defect density. With this approach, we obtained 1.75-electron volt WBG PSCs with greater than 20% power conversion efficiency, approximately 1.33-volt open-circuit voltage (
), and excellent operational stability (less than 5% degradation over 1100 hours of operation under 1.2 sun at 65°C). When further integrated with 1.25-electron volt narrow-bandgap PSC, we obtained a 27.1% efficient, all-perovskite, two-terminal tandem device with a high
of 2.2 volts.
In this article, an elasto-plastic channel-cracking model is presented to study the open-mode fracture of a thin layer brittle coating grown on a polymer substrate. A linear elastic shear interlayer ...is introduced to describe the stress transfer from the elasto-plastic substrate to the brittle coating, on basis of the shear-lag principle. The channel cracking behavior involves three stages: elastic, elasto-plastic and plastic stages, which are solved in a continuous manner based on the deformation status of the substrate. Explicit solutions are derived for the mutli-stage cracking process. Corresponding experimental tests for a titanium oxide (TiO2) coating on a poly (ethylene terephthalate) substrate are conducted. The fracture toughness of the coating layer is estimated based on the crack spacing versus layer thickness relationship at certain strain levels. This method is found to be more reliable than the traditional methods using crack onset strain. Parametric studies of the fracture energy release rate for the coating and interfacial compliance of the thin film system are conducted, through which the effect of plastic deformation on the channel cracking behavior is studied extensively. The results indicate that the tangent modulus of the substrate controls the evolution curvature of crack spacing where a smaller tangent modulus corresponds to a slower saturation of crack spacing. The energy release rate also varies significantly with the properties of the interlayer. The study highlights the necessity of an elasto-plastic model for the thin film systems of brittle coating on a plastic substrate.
Bifacial photovoltaics (PV) harvest solar irradiance from both their front and rear surfaces, boosting energy conversion efficiency to maximize their electrical power production. For single-junction ...perovskite solar cells (PSCs), the performance of bifacial configurations is still far behind that of their state-of-the-art monofacial counterparts. Here, we report on highly efficient, bifacial, single-junction PSCs based on the p-i-n (or inverted) architecture. We used optical and electrical modeling to design a transparent conducting rear electrode for bifacial PSCs to enable optimized efficiency under a variety of albedo illumination conditions. The bifaciality of the PSCs was about 91%–93%. Under concurrent bifacial measurement conditions, we obtained equivalent, stabilized bifacial power output densities of 26.9, 28.5, and 30.1 mW/cm2 under albedos of 0.2, 0.3, and 0.5, respectively. We further showed that bifacial perovskite PV technology has the potential to outperform its monofacial counterparts with higher energy yields and lower levelized cost of energy (LCOE).
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•High-efficiency p-i-n single-junction bifacial perovskite solar cells are reported•Optical and electrical modeling improves the transparent rear electrode design•Bifaciality of >91% and a front-illumination efficiency of >23% are achieved•Bifacial output powers are 28.5 mW/cm2 (albedo = 0.3) and 30.1 mW/cm2 (albedo = 0.5)
The performance of bifacial single-junction perovskite solar cells is still far behind that of their state-of-the-art monofacial counterparts. It is challenging to achieve high bifaciality and high front-side illumination efficiency simultaneously. We used optical and electrical modeling to guide the optimization of the transparent conducting rear electrode and perovskite absorber layer using a p-i-n device architecture, achieving a high bifaciality of about 91%–93% and a high front-side illumination PCE of over 23%. Under concurrent bifacial measurement conditions, the equivalent, stabilized bifacial power output densities are 26.9, 28.5, and 30.1 mW/cm2 under albedos of 0.2, 0.3, and 0.5, respectively. Through energy yield and levelized cost of energy analysis, we showed that bifacial perovskite photovoltaics technology has the potential to outperform its monofacial counterparts.
By optimizing the transparent rear electrode, we achieved highly efficient single-junction bifacial perovskite solar cells (PSCs). Under concurrent bifacial illumination conditions, we achieved stabilized power outputs of 26.9, 28.5, and 30.1 mW/cm2 under albedos of 0.2, 0.3, and 0.5, respectively—surpassing state-of-the-art monofacial single-junction PSCs and comparable to all-perovskite monofacial and bifacial tandem PSCs. Bifacial perovskite photovoltaics technology has the potential to outperform its monofacial counterparts with higher energy yields and lower levelized cost of energy.
In this study, an elasto-plastic channel-cracking model is presented to study the open-mode fracture of a thin layer brittle coating grown on a polymer substrate. A linear elastic shear interlayer is ...introduced to describe the stress transfer from the elasto-plastic substrate to the brittle coating, on basis of the shear-lag principle. The channel cracking behavior involves three stages: elastic, elasto-plastic and plastic stages, which are solved in a continuous manner based on the deformation status of the substrate. Explicit solutions are derived for the mutli-stage cracking process. Corresponding experimental tests for a titanium oxide (TiO2) coating on a poly (ethylene terephthalate) substrate are conducted. The fracture toughness of the coating layer is estimated based on the crack spacing versus layer thickness relationship at certain strain levels. This method is found to be more reliable than the traditional methods using crack onset strain. Parametric studies of the fracture energy release rate for the coating and interfacial compliance of the thin film system are conducted, through which the effect of plastic deformation on the channel cracking behavior is studied extensively. The results indicate that the tangent modulus of the substrate controls the evolution curvature of crack spacing where a smaller tangent modulus corresponds to a slower saturation of crack spacing. The energy release rate also varies significantly with the properties of the interlayer. The study highlights the necessity of an elasto-plastic model for the thin film systems of brittle coating on a plastic substrate.
The structural stability of the metal halide perovskite (MHP) absorber material is crucial for the long-term solar cell stability in this thin-film photovoltaic technology. Here, we use mixed A-site ...FA0.83Cs0.17PbI3 to demonstrate that nanoscale compositional heterogeneity can serve as initiation sites for more macroscale, irreversible phase segregation, which causes device performance degradation. Probing compositional heterogeneity on length scales that has not been detected with conventional characterization techniques, we analyze the tetragonal to cubic phase transition behavior to indirectly determine the level of nanoscale compositional heterogeneity in the initial films. Further, we show that the thermal annealing conditions of the MHP layer during film processing influence the initial nanoscale compositional heterogeneity, and changing these processing conditions can be used to improve the device performance stability. The insights into structural degradation mechanisms initiated by nanoscale compositional heterogeneity and the proposed mitigation strategies will help guide the way toward long-term stable MHP solar cells.
Metal halide perovskite solar cells have reached a critical point in their development. At a current certified record efficiency of 25.7% for a single-junction, research-scale cell, they now garner ...serious attention from the solar cell industry as a promising route to widespread, low-cost photovoltaics in single- or tandem-junction configurations. However, more work to demonstrate their durability under real-world outdoor test conditions is necessary to ensure the long-term success and deployment of the technology. Differences in chemistry, processes, and their combination result in unique performance limiters for both efficiency and stability. Further, as many active formulations and layer/cell stack combinations are sensitive to temperature, air, and moisture, it is important to separate intrinsic limitations to stability relative to these extrinsic sources. This presents a particular need for the development of an appropriate and reliable package for environmental (i.e., accelerated and outdoor) testing that will permit these different factors to be evaluated and understood.
Here we investigate tin oxide growth on fullerene (C60) by atomic layer deposition (ALD) for C60/oxide bilayer electron selective contacts in P-I-N metal halide perovskite (MHP) solar cells. An in ...situ ozone functionalization step is incorporated in an ALD SnOx process to suppress sub-surface growth, leading to improved internal barrier performance of ALD SnOx thin films grown on fullerene surfaces. We show that this approach decreases the water-vapor transmission rate of C60/ALD SnOx barriers by an order of magnitude and improves the barrier properties against gas, solvent, and halide migration. Furthermore, ozone-treated SnOx barriers can narrow photovoltaic performance distribution without compromising efficiency. We demonstrate the universality of this approach in wide-, intermediate-, and low-gap perovskite systems and further show that enhancement of the ALD barrier layer is critical toward improving the yield of all-perovskite tandem solar cells. Two-terminal all-perovskite tandem solar cells incorporating ozone nucleation are reported at over 24% photovoltaic conversion efficiency.
Metal halide perovskite photovoltaic performance required for commercial technology encompasses both efficiency and stability. Advances in both these parameters have recently been reported; however, ...these strategies are often difficult to directly compare due to differences in perovskite composition, device architecture, fabrication methods, and accelerated stressors applied in stability tests. In particular, it is found that there is a distinct lack of elevated temperature, operational (light and bias) stability data. Furthermore, significant testing is required to understand the interactions when combinations are used (e.g., additives used with posttreatments). Herein, individual and combined additive, posttreatment, and contact layer strategies from recent literature reports under standardized operational stability tests of p–i–n CsMAFA perovskites at 70 °C are evaluated. Through analysis of over 1000 devices, it is concluded that the hole‐transport layer (HTL) is the most significant component impacting elevated temperature operational stability. This analysis motivates future development of high‐performance HTLs.
Herein, interface and bulk passivation strategies applied to p–i–n metal halide perovskite solar cells under accelerated testing at 70 °C and illumination are compared. This work finds that the hole‐transport layer (HTL)/perovskite interface has the largest stability impact at elevated temperature and motivates the development of high‐performance HTLs.
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