Currently, the efficiency of perovskite solar cells (PSCs) is ≈24%. For the fabrication of such high efficiency PSCs, it is necessary to use both electron and hole transport layers to effectively ...separate the charges generated by light absorption of the perovskite layer and selectively transfer the separated electrons and holes. In addition to the efficiency, the materials used for transporting charges must be resilient to light, heat, and moisture to ensure long‐term stability of PSCs; furthermore, low‐cost fabrication is required to form a charge transport layer at low temperatures by a solution process. For this purpose, metal oxides are best suited as charge transport materials for PSCs because of their advantages such as low cost, long‐term stability, and high efficiency. In this Review, the metal oxide electron and hole transport materials used in PSCs are reviewed and preparation of these materials is summarized. Finally, the challenges and future research direction for metal oxide‐based charge transport materials are described.
Metal oxides are used as charge transporting layers to effectively separate the photogenerated electrons and holes in perovskite solar cells (PSCs). The metal oxide layers require a wide bandgap, a good charge mobility, and a compatible band alignment with the perovskite layers. This review summarizes and correlates the preparation and performance of the various metal oxides used in PSCs.
In perovskite solar cells, the interfaces between the perovskite and charge-transporting layers contain high concentrations of defects (about 100 times that within the perovskite layer), ...specifically, deep-level defects, which substantially reduce the power conversion efficiency ofthe devices1-3. Recent efforts to reduce these interfacial defects have focused mainly on surface passivation4-6. However, passivating the perovskite surface that interfaces with the electron-transporting layer is difficult, because the surface-treatment agents on the electron-transporting layer may dissolve while coating the perovskite thin film. Alternatively, interfacial defects may not be a concern if a coherent interface could be formed between the electron-transporting and perovskite layers. Here we report the formation of an interlayer between a SnO2 electron-transporting layer and a halide perovskite light-absorbing layer, achieved by coupling Cl-bonded SnO2 with a Cl-containing perovskite precursor. This interlayer has atomically coherent features, which enhance charge extraction and transport from the perovskite layer, and fewer interfacial defects. The existence of such a coherent interlayer allowed us to fabricate perovskite solar cells with a power conversion efficiency of 25.8 per cent (certified 25.5 per cent)under standard illumination. Furthermore, unencapsulated devices maintained about 90 per cent oftheir initial efficiency even after continuous light exposure for 500 hours. Our findings provide guidelines for designing defect-minimizing interfaces between metal halide perovskites and electron-transporting layers.
Abstract
To boost the photoelectrochemical water oxidation performance of hematite photoanodes, high temperature annealing has been widely applied to enhance crystallinity, to improve the interface ...between the hematite-substrate interface, and to introduce tin-dopants from the substrate. However, when using additional dopants, the interaction between the unintentional tin and intentional dopant is poorly understood. Here, using germanium, we investigate how tin diffusion affects overall photoelectrochemical performance in germanium:tin co-doped systems. After revealing that germanium is a better dopant than tin, we develop a facile germanium-doping method which suppresses tin diffusion from the fluorine doped tin oxide substrate, significantly improving hematite performance. The NiFeO
x
@Ge-PH photoanode shows a photocurrent density of 4.6 mA cm
−2
at 1.23 V
RHE
with a low turn-on voltage. After combining with a perovskite solar cell, our tandem system achieves 4.8% solar-to-hydrogen conversion efficiency (3.9 mA cm
−2
in NiFeO
x
@Ge-PH/perovskite solar water splitting system). Our work provides important insights on a promising diagnostic tool for future co-doping system design.
•The overall goal of this study is to develop an effective, simple, aptly computer vision algorithm to detect and count citrus on the tree using image processing techniques, to estimate the yield, ...and to compare the yield estimation results obtained through several methods.•This new citrus recognition and counting algorithm was utilized the color features (or schemes) to present an estimate of the citrus yield, and the corresponding models are developed to provide an early estimation of the citrus yield.•Citrus images were taken from Jeju, South Korea during daylight and the citrus recognition and counting algorithm were tested on 84 images, which were collected from 21 trees.•The citrus counting algorithm consisted of the following steps: convert RGB image to HSV, thresholding, orange color detection, noise removal, watershed segmentation, and counting.•Distance transform and marker-controlled watershed algorithms were evaluated for automated watershed segmentation in citrus fruits to obtain good result.•A correlation coefficient R2 of 0.93 was obtained between the citrus counting algorithm and counting performed through human observation.•The proposed algorithm showed great potential for early prediction of the yield of single citrus trees and the possibility of its uses for further fruit crops.
The overall goal of this study is to develop an effective, simple, aptly computer vision algorithm to detect and count citrus on the tree using image processing techniques, to estimate the yield, and to compare the yield estimation results obtained through several methods. This new citrus recognition and counting algorithm was utilized the color features (or schemes) to present an estimate of the citrus yield, and the corresponding models are developed to provide an early estimation of the citrus yield. Citrus images were taken from Jeju, South Korea during daylight and the citrus recognition and counting algorithm were tested on 84 images which were collected from 21 trees. The citrus counting algorithm consisted of the following steps: convert RGB image to HSV, thresholding, orange color detection, noise removal, watershed segmentation, and counting. Distance transform and marker-controlled watershed algorithms were evaluated for automated watershed segmentation in citrus fruits to obtain good result. A correlation coefficient R2 of 0.93 was obtained between the citrus counting algorithm and counting performed through human observation. The proposed algorithm showed great potential for early prediction of the yield of single citrus trees and the possibility of its uses for further fruit crops.
Cholesteric liquid crystals (CLCs), also known as chiral nematic LCs, show a photonic stopband, which is promising for various optical applications. In particular, CLCs confined in microcompartments ...are useful for sensing, lasing, and optical barcoding at the microscale. The integration of distinct CLCs into single microstructures can provide advanced functionality. In this work, CLC multishells with multiple stopbands are created by liquid–liquid phase separation (LLPS) in a simple yet highly controlled manner. A homogeneous ternary mixture of LC, hydrophilic liquid, and co‐solvent is microfluidically emulsified to form uniform oil‐in‐water drops, which undergo LLPS to form onion‐like drops composed of alternating CLC‐rich and CLC‐depleted layers. The multiplicity is controlled from one to five by adjusting the initial composition of the ternary mixture, which dictates the number of consecutive steps of LLPS. Interestingly, the concentration of the chiral dopant becomes reduced from the outermost to the innermost CLC drop due to uneven partitioning during LLPS, which results in multiple stopbands. Therefore, the photonic multishells show multiple structural colors. In addition, dye‐doped multishells provide band‐edge lasing at two different wavelengths. This new class of photonic multishells will provide new opportunities for advanced optical applications.
Photonic multishells are created by controlled phase separation of cholesteric liquid crystals and hydrophilic liquid confined in emulsion drops. The material exchange between the dispersed and continuous phases triggers the consecutive steps of phase separation, through which onion‐like drops are formed. Multiple photonic stopbands are spontaneously developed by uneven partitioning of the chiral dopant, which provides advanced photonic functionality.
Mn-doped SnO
2
thin films were fabricated to enhance two conflicting properties of the electromagnetic interference (EMI) shielding effectiveness and the infrared (IR) wavelength ranges. As a ...magnetic element, manganese (Mn) was doped into the SnO
2
thin films at an over-doping level of 300 mM to increase its magnetic permeability. As the molar content of Mn increases, the preferred growth plane of the SnO
2
thin films changes from (200) to (115) planes. Although all SnO
2
thin films showed diamagnetic properties due to the strong diamagnetism of the substrate and SnO
2
, the magnetic susceptibility of the Mn-doped SnO
2
films slightly decreased with increasing the Mn content from 0 to 60 mM, while it increased again with the doping content above it. As the Mn doping content increased from 0 to 150 mM, the sheet resistance of SnO
2
films continuously increased from 98 to 128 Ω/sq. As the Mn content increases from 30 to 120 mM, the IR transmittance at 4 μm increases from 37 to 47%, while the EMI shielding effectiveness at 10 GHz increases from 8.7 to 9.0 dB. The abnormal result of increased shielding effectiveness despite increased sheet resistance was due to increased magnetic permeability due to the addition of Mn. As the Mn content exceeds 150 mM, Mn-related metal clusters are formed inside the thin film, reducing the magnetic susceptibility and EMI shielding.
The switch between stem/progenitor cell expansion and differentiation is critical for organ homeostasis. The mammalian Hippo pathway effector and oncoprotein YAP expands undifferentiated ...stem/progenitor cells in various tissues. However, the YAP-associated transcription factors and downstream targets underlying this stemness-promoting activity are poorly understood. Here we show that the SRF-IL6 axis is the critical mediator of YAP-induced stemness in mammary epithelial cells and breast cancer. Specifically, serum response factor (SRF)-mediated binding and recruitment of YAP to mammary stem cell (MaSC) signature-gene promoters induce numerous MaSC signature genes, among which the target interleukin (IL)-6 is critical for YAP-induced stemness. High SRF-YAP/TAZ expression is correlated with IL6-enriched MaSC/basal-like breast cancer (BLBC). Finally, we show that this high SRF expression enables YAP to more efficiently induce IL6 and stemness in BLBC compared with luminal-type breast cancer. Collectively, our results establish the importance of SRF-YAP-IL6 signalling in promoting MaSC-like properties in a BLBC-specific manner.
The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and ...mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
We report all solid-state nanostructured inorganic−organic heterojunction solar cells fabricated by depositing Sb2S3 and poly(3-hexylthiophene) (P3HT) on the surface of a mesoporous TiO2 layer, where ...Sb2S3 acts as an absorbing semiconductor and P3HT acts as both a hole conductor and light absorber. These inorganic−organic light harvesters perform remarkably well with a maximum incident-photon-to-current efficiency (IPCE) of 80% and power conversion efficiency of 5.13% under air-mass 1.5 global (AM 1.5G) illumination with the intensity of 100 mW cm−2. These devices are highly stable under room light in air, even without encapsulation. The present findings offer novel directions for achieving high-efficiency solid-state solar cells by hybridization of inorganic−organic light harvesters and hole transporters.
Most methods that are used to evaluate the performance degradation of engine oil require considerable amounts of the engine oil. Hence, novel techniques that require only small amounts of samples are ...needed. In this study, we investigated the feasibility of using the viscosity of and the intensity of light transmitted from a small amount of engine oil to evaluate the degradation of the oil. The viscosity was measured through repeated evaluations of the flow conditions using a fine capillary tube. The light intensity transmitted through the sample oil was measured using a light-emitting diode and photodiode. Using the two evaluation methods, we analyzed six oil samples that had undergone different durations of usage. Subsequently, the correlation between the durations and measured values was examined. The results indicated that the viscosity and light intensity decreased with increase in the duration of usage. From these results, we found that our viscosity and transmitted light intensity measurement methods could be used to evaluate the degradation of engine oil using small amounts of the oil. In addition, the transmitted light intensity can be used to estimate turbidity.
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•Two methods were proposed to evaluate degradation in small volume oil samples.•One evaluation method is measuring viscosity, and another is measuring intensity of transmitted LED light.•Shell 15W40-DH2 engine oil was used as the evaluation sample after 58.3–1567.8 h of use in an engine.•Degradation could be evaluated by each method.•We clarified correlation between two proposed methods.
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