Understanding and Weakening Photon Recycling in Solar Cells to Approach the Radiative Limit.

Photon recycling plays an important role in the light outcoupling of state-of-the-art solar cells and is considered a necessary condition to achieve the radiative limit of open-circuit voltage (VOC) and efficiency. However, due to the impact of photon recycling on bulk and surface radiation of solar cells being overlooked, experimental demonstrations on the accuracy of existing photon recycling models are scarce and some contrary theoretical results also emerge. Here, the relationship between photon recycling and radiation processes, as well as the corresponding VOC losses of solar cells based on the principle of detailed balance is clarified. It is shown that weakening photon recycling is more effective to boost the device performance than enhancing it, promoting the theoretical efficiencies of solar cells, such as perovskite, Si, and GaAs, to 98.5%, 94.9%, and almost 100% of their radiative limit, respectively. Moreover, weakening photon recycling also helps to maintain higher efficiency when the internal radiative efficiency decreases, which benefits higher device stability. This work provides an in-depth understanding of the role of photon recycling in solar cells and helps to push efficiency to a new limit.

Physically and Chemically Stable Molybdenum-Based Composite Electrodes for p-i-n Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs) have garnered much attention in recent years. Despite the remarkable advancements in PSCs utilizing traditional metal electrodes, challenges such as stability concerns and elevated costs have necessitated the exploration of innovative electrode designs to facilitate industrial commercialization. Herein, a physically and chemically stable molybdenum (Mo) electrode is developed to fundamentally tackle the instability factors introduced by electrodes. The combined spatially resolved element analyses and theoretical study demonstrate the high diffusion barrier of Mo ions within the device. Structural and morphology characterization also reveals the negligible plastic deformation and halide-metal reaction during aging when Mo is in contact with perovskite (PVSK). The electrode/underlayer junction is further stabilized by a thin seed layer of titanium (Ti) to improve Mo film's uniformity and adhesion. Based on a corresponding p-i-n PSCs (ITO/PTAA/PVSK/C60/SnO2/ITO/Ti/Mo), the champion sample could deliver an efficiency of 22.25%, which is among the highest value for PSCs based on Mo electrodes. Meanwhile, the device shows negligible performance decay after 2000 h operation, and retains 91% of the initial value after 1300 h at 50-60 °C. In summary, the multilayer Mo electrode opens an effective avenue to all-round stable electrode design in high-performance PSCs.

Isolating the Oxygen Adsorption Defects on Sputtered Tin Oxide for Efficient Perovskite Solar Cells.

Tin oxide (SnO2) is the most commonly used electron transport material for perovskite solar cells (PSCs). Various techniques have been applied to deposit tin dioxide, including spin-coating, chemical bath deposition, and magnetron sputtering. Among them, magnetron sputtering is one of the most mature industrial deposition techniques. However, PSCs based on magnetron-sputtered tin oxide (sp-SnO2) have a lower open-circuit voltage (Voc) and power conversion efficiency (PCE) than those prepared by the mainstream solution method. This is mainly due to the oxygen-related defects at the sp-SnO2/perovskite interface, and traditional passivation strategies usually have little effect on them. Herein, we successfully isolate the oxygen adsorption (Oads) defects located on the surface of sp-SnO2 from the perovskite layer using a PCBM double-electron transport layer. This isolation strategy effectively suppresses the Shockley-Read-Hall recombination at the sp-SnO2/perovskite interface, which results in an increase in the Voc from 0.93 to 1.15 V and an increase in PCE from 16.66 to 21.65%. To our knowledge, this is the highest PCE achieved using a magnetron-sputtered charge transport layer to date. The unencapsulated devices maintain 92% of their initial PCE after storage in air with a relative humidity of 30-50% after 750 h. We further use the solar cell capacitance simulator (1D-SCAPS) to confirm the effectiveness of the isolation strategy. This work highlights the application prospect of magnetron sputtering in the field of perovskite solar cells and provides a simple yet effective way to tackle the interfacial defect issue.

Flexible and Conductive Polymer Threads for Efficient Fiber-Shaped Supercapacitors via Vapor Copolymerization.

Flexible fiber electrodes are critical for high-performance fiber and wearable electronics. In this work, we presented a highly conductive all-polymer fiber electrode by vapor copolymerization of 2,5-dibromo-3,4-vinyldioxythiophene (DBEDOT) and 2,5-diiodo-3,4-vinyldioxythiophene (DIEDOT) monomers on commonly used polyester threads (PETs) at a temperature as low as 80 °C. The poly(3,4-ethylenedioxythiophene) (PEDOT)-coated PET threads maintain excellent flexibility and show conductivity of 7.93 S cm-1, nearly four times higher than that reported previously via homopolymerization of DBEDOT monomer. A MnO2 active layer was embedded into the PEDOT double layers, and the flexible fiber composite electrode showed a high linear specific capacitance of 157 mF cm-1 and improved stability, retaining 86.5% capacitance after 5000 cycles. Fiber-shaped solid-state supercapacitors (FSSCs) based on the composite electrodes were assembled, and they displayed superior electrochemical performance. This work provides a new approach to realize high-performance and stable wearable electronics.

Doping Mechanism of Perovskite Films with PbCl2 Prepared by Magnetron Sputtering for Enhanced Efficiency of Solar Cells.

The last decade has witnessed a rapid growth of perovskite solar cells extended from mesoporous to planar architecture as well as from solution processing to solvent-free fabrication. The preparation of perovskite films by solvent-free method still presents significant challenges, such as the difficulty of film preparation by multiple evaporation sources in vapor deposition and the immaturity of the sputtered method. Here, we present a planar perovskite solar cell fabricated by solvent-free magnetron sputtering without the assistance of the mesoporous TiO2 layer, and lead chloride (PbCl2) was mechanically milled into the target of methylammonium lead halides (MAPbI3) to improve the quality of perovskite film by regulating the crystallization process with the Cl element. Furthermore, the internal reason for the effect of different PbCl2 doping contents on the trap density of perovskite films was also investigated in detail. These lead to an improved power conversion efficiency of planar heterojunction perovskite solar cells up to 17.10%, which is the highest efficiency recorded for the sputtered perovskite solar cells so far. The stability of resulting solar cells has also been significantly improved by exploring the doping mechanism of perovskite films with PbCl2 in detail, showing great research and application prospect.

Photoreduction of carbon dioxide and photodegradation of organic pollutants using alkali cobalt oxides MCoO2 (M = Li or Na) as catalysts.

The recycling of lithium batteries should be prioritized, and the use of discarded alkali metal battery electrode materials as photocatalysts merits research attention. This study synthesized alkali metal cobalt oxide (MCoO2, M = Li or Na) as a photocatalyst for the photoreduction of CO2 and degradation of toxic organic substances. The optimized NaCoO2 and LiCoO2 photocatalysts increased the photocatalytic CO2-CH4 conversion rate to 21.0 and 13.4 µmol g-1 h-1 under ultraviolet light irradiation and to 16.2 and 5.3 µmol g-1 h-1 under visible light irradiation, which is 17 times higher than that achieved by TiO2 P25. The rate constants of the optimized reactions of crystal violet (CV) with LiCoO2 and NaCoO2 were 2.29 × 10-2 and 4.35 × 10-2 h-1, respectively. The quenching effect of the scavengers and electron paramagnetic resonance in CV degradation indicated that active O2•-, 1O2, and h+ play the main role, whereas •OH plays a minor role for LiCoO2. The hyperfine splitting of the DMPO-•OH and DMPO-•CH3 adducts was aN = 1.508 mT, aHß = 1.478 mT and aN = 1.558 mT, aHß = 2.267 mT, respectively, whereas the hyperfine splitting of DMPO+• was aN = 1.475 mT. The quenching effect also indicated that active O2•- and h+ play the main role and that •OH and 1O2 play a minor role for NaCoO2. The hyperfine splitting of the DMPO-•OH and DMPO+• adducts was aN = 1.517 mT, aHß = 1.489 mT and aN = 1.496 mT, respectively. Discarded alkali metal battery electrode materials can be reused as photocatalysts to address environmental pollution.

Organic-Inorganic Perovskite Films and Efficient Planar Heterojunction Solar Cells by Magnetron Sputtering.

Organic-inorganic halide perovskites have been widely used in photovoltaic technologies. Despite tremendous progress in their efficiency and stability, perovskite solar cells (PSCs) are still facing the challenges of upscaling and stability for practical applications. As a mature film preparation technology, magnetron sputtering has been widely used to prepare metals, metallic oxides, and some semiconductor films, which has great application potential in the fabrication of PSCs. Here, a unique technology where high-quality perovskite films are prepared via magnetron sputtering for controllable composition, solvent-free, large-area, and massive production, is presented. This strategy transforms the perovskite materials from powder to thin films by magnetron sputtering and post-treatment (vapor-assisted treatment with methanaminium iodide gas and methylamine gas treatment), which is greatly favorable to manufacture tandem solar cells. The power conversion efficiency (PCE) of PSCs with perovskite films fabricated by magnetron sputtering is 6.14%. After optimization, high-performance perovskite films with excellent electronic properties are obtained and stable PSCs with excellent reproducibility are realized, showing a PCE of up to 15.22%. The entirely novel synthetic approach opens up a new and promising way to achieve high-throughput magnetron sputtering for large-area production in commercial applications of planar heterojunction and tandem PSCs.

Visible-light-driven photocatalysis of carbon dioxide and organic pollutants by MFeO2 (M = Li, Na, or K).

In recent years, lithium-containing ceramic materials have attracted considerable research attention as high-temperature adsorbents of carbon dioxide. The recycling of electrode materials from spent lithium-ion batteries for use as photocatalysts in recovering CO2 and degrading organic pollutants is worthy of exploration. Solid, magnetic ferrite-containing photocatalysts are easily separated from reaction solutions by using magnetic devices. Solid catalysts (e.g., LiFeO2, LiFe5O8, NaFeO2, and K2Fe2O4) were prepared through the calcination of Fe2O3 and M2CO3. CO2 was photoreduced and crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) were photodegraded under visible light irradiation. The optimized K2Fe2O4 photocatalyst increased the rate of photocatalytic conversion from CO2 to methane at 20.9 µmol g-1 h-1. The catalytic efficiency indicated that the optimized reaction rate constants of CV with LiFeO2, NaFeO2, and K2Fe2O4 were 2.98 × 10-1, 5.32 × 10-1, and 4.36 × 10-1 h-1, respectively. The quenching effect achieved through the use of various scavengers and the electron paramagnetic resonance in CV degradation revealed the substantial contribution of the reactive superoxide anion radical O2- and the minor roles of h+ and the OH radical. Its usefulness in the synthesis of solid-base catalyst MFeO2 is promising for environmental control and relevant applications, particularly in solar energy manufacturing.

Mechanochemical synthesis of pure phase mixed-cation/anion (FAPbI3) x (MAPbBr3)1-x hybrid perovskite materials: compositional engineering and photovoltaic performance.

Organic-inorganic hybrid perovskites have emerged as promising light harvesting materials for many optoelectronic devices. Here, we present a facile mechanochemical synthesis (MCS) route for the preparation of a series of pure phase mixed-cation/anion (FAPbI3) x (MAPbBr3)1-x (0 ≤ x ≤ 1) hybrid perovskite materials for high-efficiency thin-film perovskite solar cells (PSCs). The use of (α-FAPbI3)0.95(MAPbBr3)0.05 perovskite prepared by MCS for the thin-film PSCs achieves a maximum PCE of 15.9% from a current-voltage (J-V) scan, which stabilises at 15.4% after 120 s of the maximum power point output. Furthermore, PSCs based on (KPbI3)0.05(FAPbI3)0.9(MAPbBr3)0.05 perovskite prepared by MCS exhibit higher photovoltaic performance and lower hysteresis compared with (α-FAPbI3)0.95(MAPbBr3)0.05, with a maximum PCE of 16.7%. These results indicate that the use of mechanochemically synthesised perovskites provides a promising strategy for high performance PSCs and superior control in optoelectronic properties, leading to improved control in fabrication approaches and facilitating the development of efficient and stable PSCs in the future.

Solvent-Free Mechanochemical Synthesis of a Systematic Series of Pure-Phase Mixed-Halide Perovskites MAPb(Ix Br1-x )3 and MAPb(Brx Cl1-x )3 for Continuous Composition and Band-Gap Tuning.

Hybrid perovskites have recently received much attention in optoelectronic applications. However, hybrid perovskites are unstable in a humid environment. Mixed halide perovskites (MHPs) show enhanced stability and band-gap tunability upon engineering of their halide composition. Here, MHPs are prepared through a solvent-free mechanochemical synthesis (MCS) route that allows superior control over halide compositions than the solvent synthesis routes (SS). The MCS route eliminates the problem in the preparation of MAPb(Ix Br1-x )3 with continuously varying x, while maintaining the material properties and suppressing phase segregation present in SS routes. UV-vis absorption and X-ray diffraction patterns confirm the production of the desired pure-phase MHPs. For MAPb(Ix Br1-x )3 (0≤x≤1), with increased ratio of halide (x), the cubic phase gradually transforms into the tetragonal phase and band-gap tunability is accomplished. The MCS route for the preparation of MHPs is a very promising and efficient technique for superior control in optoelectronic properties, leading to improved control in fabrication approaches.

Gender Differences in the Association between Serum Uric Acid and Prediabetes: A Six-Year Longitudinal Cohort Study.

This study aimed to examine gender differences in the association between serum uric acid (SUA) and the risk of prediabetes in a longitudinal cohort. A total of 8237 participants in the Beijing Health Management Cohort study were recruited and surveyed during 2008⁻2009, and followed up in 2011⁻2012 and 2014⁻2015 surveys. Generalized estimating equation (GEE) models were used to evaluate the association between SUA and prediabetes. Furthermore, subgroup analyses assessed the primary outcome according to status of abdominal obesity, age and status of hypertension. During six years of follow-up, we identified 1083 prediabetes events. The GEE analyses confirmed and clarified the association between SUA and prediabetes (RR = 1.362; 95% CI = 1.095⁻1.696; p = 0.006) after adjusting for other potential confounders, especially in females (RR = 2.109; 95% CI = 1.329⁻3.347; p = 0.002). In addition, this association was stronger in the subgroup of females aged ≥48 years old (RR = 2.384; 95% CI = 1.417⁻4.010; p = 0.001). The risk for prediabetes increased significantly with increasing SUA for females in the Chinese population. This association was strongly confirmed in older females aged ≥48 years old rather than in younger females, which may provide clues for pathogenic mechanisms of gender differences in the association between SUA and prediabetes.

Two-Year Changes in Hyperuricemia and Risk of Diabetes: A Five-Year Prospective Cohort Study.

BACKGROUND: Hyperuricemia is known to be a risk factor for diabetes. However, information is limited regarding the association between changes in hyperuricemia and the risk of diabetes. METHODS: A total of 15,403 participants who were free of diabetes at the time of 2009 and 2011 surveys in the Beijing Health Management Cohort (BHMC) study were recruited and followed up until 2016. Participants were classified into four groups according to 2-year changes in hyperuricemia: no hyperuricemia, remittent hyperuricemia, incident hyperuricemia, and persistent hyperuricemia. Modified Poisson regression models were used to evaluate the effect of 2-year changes in hyperuricemia on the risk of diabetes. RESULTS: During the 5-year follow-up, we identified 841 new cases of diabetes (216 women). Remittent hyperuricemia and incident hyperuricemia had a 35% and 48% higher risk for developing diabetes compared with no hyperuricemia. Especially, persistent hyperuricemia was associated with a 75% higher risk of diabetes (RR = 1.75, 95% CI = 1.47-2.08). Compared with minor serum uric acid (SUA) change, over 10% decline and over 30% increase in SUA levels were subsequently associated with lower (RR = 0.84, 95% CI = 0.72-0.99) and higher (RR = 1.71, 95% CI = 1.27-2.30) diabetes risk, respectively. CONCLUSIONS: Changes in hyperuricemia, especially persistent hyperuricemia, are more appropriate to reflect the risk of diabetes than a single measurement of hyperuricemia at baseline. Strategies aiming at preventing hyperuricemia are urgently needed to reduce the increasing burden of diabetes.

Memristive property's effects on the I-V characteristics of perovskite solar cells.

The unfavorable I-V characteristics of perovskite solar cells (PSCs), such as the I-V hysteresis phenomena, have been one major obstacle for their future practical application. However, corresponding analysis based on traditional theories have shown non-negligible flaws and failed for satisfactory explanation. To present a novel mechanism, here we utilize for the first time the memristive property of the perovskite material to analyze the I-V characteristics of PSCs. The obtained joint physical model and the deduced equation may help solving the long-existent mysteries of the I-V characteristics of PSCs. On the basis of our analysis and memristor theory, we also propose an original device optimization strategy for PSCs, which may help further increase their performance to the limit.

Improved hole-transporting property via HAT-CN for perovskite solar cells without lithium salts.

A nonadditive hole-transporting material (HTM) of a triphenylamine derivative of N,N'-di(3-methylphenyl)-N,N'-diphenyl-4,4'-diaminobiphenyl (TPD) is used for the organic-inorganic hybrid perovskite solar cells. The power conversion efficiency (PCE) can be significantly enhanced by inserting a thin layer of 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) without adding an ion additive because the hole-transporting properties improve. The short-circuit current density (J(sc)) increases from 8.5 to 13.1 mA/cm(2), the open-circuit voltage (V(oc)) increases from 0.84 to 0.92 V, and the fill-factor (FF) increases from 0.45 to 0.59, which corresponds to the increase in PCE from 3.2% to 7.1%. Moreover, the PCE decreases by only 10% after approximately 1000 h without encapsulation, which suggests an alternative method to improve the stability of perovskite solar cells.

Dye-sensitized solar cells with vertically aligned TiO2 nanowire arrays grown on carbon fibers.

One-dimensional semiconductor TiO2 nanowires (TNWs) have received widespread attention from solar cell and related optoelectronics scientists. The controllable synthesis of ordered TNW arrays on arbitrary substrates would benefit both fundamental research and practical applications. Herein, vertically aligned TNW arrays in situ grown on carbon fiber (CF) substrates through a facile, controllable, and seed-assisted thermal process is presented. Also, hierarchical TiO2 -nanoparticle/TNW arrays were prepared that favor both the dye loading and depressed charge recombination of the CF/TNW photoanode. An impressive conversion efficiency of 2.48 % (under air mass 1.5 global illumination) and an apparent efficiency of 4.18 % (with a diffuse board) due to the 3D light harvesting of the wire solar cell were achieved. Moreover, efficient and inexpensive wire solar cells made from all-CF electrodes and completely flexible CF-based wire solar cells were demonstrated, taking into account actual application requirements. This work may provide an intriguing avenue for the pursuit of lightweight, cost-effective, and high-performance flexible/wearable solar cells.

Macroscopic, flexible, high-performance graphene ribbons.

Tailoring the structure and properties of graphene fibers is an important step toward practical applications. Here, we report macroscopic, long graphene ribbons formed by combining electrostatic interaction and shear stress during the wet-spinning process. The graphene ribbons are flexible and can be woven into complex structures, and the ribbon morphology can be tailored by controlling the orientation of wrinkles to obtain elasticity within a modest strain. We demonstrate several potential applications of pure or Pt-graphene hybrid ribbons as elastic strain sensors, counter electrodes for dye-sensitized fiber solar cells with cell efficiencies reaching 4.69% under standard illumination and 6.41% with a back reflector, and woven fabric supercapacitor electrodes. Our method can directly fabricate meter-long graphene ribbons with controlled structure and high performance as both energy conversion and energy storage materials.

Vibration test method to study elastic stability of porous carbon nanocomposite counter electrode in dye sensitized solar cells.

An out-of-plane elastic vibration test method is developed to directly study the elastic stability of elastic Ti foil-supported porous carbon nanocomposite (CNC) counter electrode (CE) of dye sensitized solar cells (DSSCs). The stability of CE, estimated by that of power conversion efficiency (PCE) of the CE-based DSSC device, is studied from the views of CNC morphology, equivalent resistances, exchange current density and contact model of CE. The results suggest thinner thickness and bigger interbundling degree of CNC layer is beneficial to the total internal impedance value of CE, and then beneficial to the CE stability. With optimal CNC structure, even if the CE is springed 1000 times with max amplification about 10 mm, the PCE of CE-based DSSC can remain 80% of the initial value. The test method is interesting and the results may have a potential use for elastic stability study of general elastic devices.

Fiber supercapacitors utilizing pen ink for flexible/wearable energy storage.

A novel type of flexible fiber/wearable supercapacitor that is composed of two fiber electrodes - a helical spacer wire and an electrolyte - is demonstrated. In the carbon-based fiber supercapacitor (FSC), which has high capacitance performance, commercial pen ink is directly utilized as the electrochemical material. FSCs have potential benefits in the pursuit of low-cost, large-scale, and efficient flexible/wearable energy storage systems.

A dendron modified ruthenium complex: enhanced open circuit voltage in dye-sensitized solar cells.

The novel ruthenium complex RG1, bearing dendritic structures, can act not only as a dye but also as an additive in the electrolytes, leading to slow charge recombination and high open-circuit voltage even without 4-tert-butylpyridine in both iodine and cobalt electrolytes.

Highly efficient and completely flexible fiber-shaped dye-sensitized solar cell based on TiO2 nanotube array.

A type of highly efficient completely flexible fiber-shaped solar cell based on TiO(2) nanotube array is successfully prepared. Under air mass 1.5G (100 mW cm(-2)) illumination conditions, the photoelectric conversion efficiency of the solar cell approaches 7%, the highest among all fiber-shaped cells based on TiO(2) nanotube arrays and the first completely flexible fiber-shaped DSSC. The fiber-shaped solar cell demonstrates good flexibility, which makes it suitable for modularization using weaving technologies.