Flexible perovskite solar cells have attracted widespread research effort because of their potential in portable electronics. The efficiency has exceeded 18 % owing to the high‐quality perovskite ...film achieved by various low‐temperature fabrication methods and matching of the interface and electrode materials. This Review focuses on recent progress in flexible perovskite solar cells concerning low‐temperature fabrication methods to improve the properties of perovskite films, such as full coverage, uniform morphology, and good crystallinity; demonstrated interface layers used in flexible perovskite solar cells, considering key figures‐of‐merit such as high transmittance, high carrier mobility, suitable band gap, and easy fabrication via low‐temperature methods; flexible transparent electrode materials developed to enhance the mechanical stability of the devices; mechanical and long‐term environmental stability; an outlook of flexible perovskite solar cells in portable electronic devices; and perspectives of commercialization for flexible perovskite solar cells based on cost.
Flexible perovskite solar cells have attracted significant attention owing to their promising potential in practical applications. This Review discusses the prerequisite conditions for flexible perovskite solar cells, provides an outlook of flexible perovskite devices in portable electronic products, and estimates their production cost by roll‐to‐roll vacuum deposition for commercialization.
Abstract
Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report ...success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO
2
) electron-transport layer. The Fermi level of EDTA-complexed SnO
2
is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO
2
. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO
2
increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO
2
enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO
2
degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm
−2
.
Fullerene derivative, such as 6,6-phenyl C61 butyric acid methyl ester (PCBM), is widely used as an electron-transport layer (ETL) in inverted perovskite solar cell (PSC). However, its low electron ...mobility, complexity in achieving quality film formation, and severe nonradiative recombination at perovskite/PCBM interface due to the large electron capture region, lead to lower efficiency for inverted PSCs compared to the normal structures. Herein, we demonstrate an effective and practical strategy to overcome these challenges. Conjugated n-type polymeric materials are mixed together with PCBM to form a homogeneous bulk-mixed (HBM) continuous film with high electron mobility and suitable energy level. HBM film is found to completely cap the perovskite surface to enhance the electron extraction. The critical electron capture radius of the HBM decreases to 12.52 nm from 14.89 nm of PCBM due to the large relative permittivity, resulting in reduced nonradiative recombination at perovskite/HBM interface. The efficiency of inverted PSCs with HBM ETLs exceeds 20.6% with a high fill factor of 0.82. Further, the stability of devices is improved owing to the high hydrophobicity of the HBM ETLs. Under ambient air condition after 45 days, the efficiency of inverted PSCs based on HBM remains 80% of the initial value. This is significantly higher than the control devices which retain only 48% of the initial value under similar aging conditions. We believe these breakthroughs in improving efficiency and stability of inverted PSCs will expedite their transition.
The electron-transport layer (ETL) between the active perovskite material and the cathode plays a critical role in planar perovskite solar cells. Herein, we report a drastically improved solar cell ...efficiency via surface optimization of the TiO2 ETL using a special ionic-liquid (IL) that shows high optical transparency and superior electron mobility. As a consequence, the efficiency is promoted to as high as 19.62% (the certified efficiency is 19.42%), exceeding the previous highest efficiency recorded for planar CH3NH3PbI3 perovskite solar cells. Surprisingly, the notorious hysteresis is completely eliminated, likely due to the improved ETL quality that has effectively suppressed ion migration in the perovskite layer and charge accumulation at the interfaces, higher electron mobility to balance the hole flux at the anode, and a better growth platform for the high quality perovskite absorber. Both experimental analyses and theoretical calculations reveal that the anion group of the IL bonds to TiO2, leading to a higher electron mobility and a well-matched work function. Meanwhile, the cation group interfaces with adjacent perovskite grains to provide an effective channel for electron transport and a suitable setting to grow low trap-state density perovskite for improved device performance.
A group of dendrimers with oligo‐carbazole dendrons appended at 4,4′‐ positions of biphenyl core are synthesized for use as host materials for solution‐processible phosphorescent organic ...light‐emitting diodes (PHOLEDs). In comparison with the traditional small molecular host 4,4′‐N,N′‐dicarbazolebiphenyl (CBP), the dendritic conformation affords these materials extra merits including amorphous nature with extremely high glass transition temperatures (ca. 376 °C) and solution‐processibility, but inherent the identical triplet energies (2.60–2.62 eV). In comparison with the widely‐used polymeric host polyvinylcarbazole (PVK), these dendrimers possess much higher HOMO levels (–5.61 to –5.42 eV) that facilitate efficient hole injection and are favorable for high power efficiency in OLEDs. The agreeable properties and the solution‐processibility of these dendrimers makes it possible to fabricate highly efficient PHOLEDs by spin coating with the dendimers as phosphorescent hosts. The green PHOLED containing Ir(ppy)3 (Hppy = 2‐phenyl‐pyridine) dopant exhibits high peak efficiencies of 38.71 cd A−1 and 15.69 lm W−1, which far exceed those of the control device with the PVK host (27.70 cd A−1 and 9.6 lm W−1) and are among the best results for solution‐processed green PHOLEDs ever reported. The versatility of these dendrimer hosts can be spread to orange PHOLEDs and high efficiencies of 32.22 cd A−1 and 20.23 lm W−1 are obtained, among the best ever reported for solution‐processed orange PHOLEDs.
The dendritic analogues of small molecular phosphorescent host (4,4′‐N,N′‐dicarbazolebiphenyl (CBP)) inherit similar triplet energies and HOMO/LUMO levels to those of CBP, but exhibit extra merits of amorphous nature and solution‐processible capability. These dendrimers greatly enhance device performance in comparison with traditional polyvinylcarbazole (PVK) when used as hosts in phosphorescent organic light‐emitting diodes (PHOLEDs), representing perfect alternatives to PVK as solution‐processible phosphorescent hosts for PHOLEDs.
Micro-arc oxidation (MAO) coating was produced on the surface of Al-Ti double-layer composite plate. Different concentrations of 0–8 g/L Na2WO4 were added into the MAO electrolyte and its effects on ...the MAO behavior and coating microstructure were investigated. The results showed that the addition of Na2WO4 enhanced the MAO reaction intensity on the part of Al alloy (P-Al) in the Al-Ti composite plate and correspondingly increased the coating thickness, while the reaction intensity and coating thickness on the part of Ti alloy (P-Ti) was decreased. XRD analysis confirmed a formation of WO3 in both side coatings of the composite plate, and W6+ was detected similarly by XPS spectra. SEM observations indicated that the surface porosity and thickness of the P-Ti coating was reduced, while those of the P-Al coating was increased with the increase of Na2WO4 concentration. TEM analysis verified that corresponding oxide phases and WO3 were formed in the different MAO coatings on the P-Al or the P-Ti and the addition of Na2WO4 enhanced the coating compactness of the transition zone. EDX detection proved that W concentration in the P-Ti coating was higher than that in the P-Al coating. The nano-indentation tests showed that the hardness and Young's modulus of both side coatings were improved with adding Na2WO4. A competitive mechanism was proposed for the MAO process with the addition of Na2WO4, and the distribution of electrical energy was found to be balanced in both sides of composite plate.
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•The electrical energy distribution during the MAO process of Al-Ti double-layer composite plate was analyzed.•The distribution of electrical energy on the Al-Ti double-layer composite plate surface was improved with adding the Na2WO4.•The addition of Na2WO4 could improve the structure of MAO coating.•The influence mechanism of Na2WO4 on the MAO behavior was summarized.
In recent years, with increasing passenger travel demand, high-speed railways have developed rapidly. The stop planning and timetabling problems are the core contents of high-speed railway transport ...planning and have important practical significance for improving efficiency of passenger travel and railway operation Dong et al. (2020). This study proposes a collaborative optimization approach that can be divided into two phases. In the first phase, a mixed-integer nonlinear programming model is constructed to obtain a stop plan by minimizing the total passenger travel time. The constraints of passenger origin-destination (OD) demand, train capacity, and stop frequency are considered in the first phase. In the second phase, the train timetable is optimized after the stop plan is obtained. A multiobjective mixed-integer linear optimization model is formulated by minimizing the total train travel time and the deviation between the expected and actual departure times from the origin station for all trains. Multiple types of trains and more refined headways are considered in the timetabling model. Finally, the approach is applied to China's high-speed railway, and the GUROBI optimizer is used to solve the models in the above two stages. By analyzing the results, the total passenger travel time and train travel time decreased by 2.81% and 3.34% respectively. The proposed method generates a more efficient solution for the railway system.
This study focuses on the rescheduling problem with disruptions that cause partial blockages in the urban rail transit (URT), contributing to extending the relative train rescheduling studies. The ...alternative driving measure (ADM), which could be regarded as one train rerouting measure, is used to skip the blocked section, and a mixed-integer nonlinear programming (MINLP) model is built based on it. Time-varying passenger flow as well as the turnaround process of rolling stocks is taken into consideration. To solve the model, a customized genetic algorithm is used to quickly generate high-quality solutions. Real-world data is studied and sensitivity analyses are taken to verify the feasibility and advantage of ADM. The results validate the proposed model and algorithm, as well as confirm that ADM shows significantly better performance than the practical operation measure in promoting passenger service quality of URT under partial blockage.
SK5 steel is the base material used for the preparation of the wrinkle scraper, whose service life strongly affects the working efficiency and economic benefits. In this work, WC–Cr3C2–Ni coating was ...deposited on the SK5 steel substrate by using High-velocity air fuel spray (HVAF) and Laser cladding (LC) processes respectively, named HVAF-WC coating and LC-WC coating. The microstructure and wear resistance of both coatings were analyzed, and were compared with the substrate sample. Results showed that the coatings were adhesive well onto the substrate. More WC with fine crystals is retained in HVAF-WC coating due to low flame flow temperature, while WC of LC-WC coating is characterized by columnar crystals. The wear rate of HVAF-WC and LC-WC coating was 4.00 × 10−7 mm3/(N•m) and 3.47 × 10−6 mm3/(N•m), respectively, which was two and one orders of magnitude lower than SK5 steel with 3.54 × 10−5 mm3/Nm. HVAF-WC coating exhibited the best wear resistance because of significant fine grain strengthening, which wear mechanism is mainly dominated by abrasive wear. Thus, it was thought that HVAF-WC coating is more effective ways to improve the wear resistance of SK5 steel, comparing with LC-WC coating.
Metallothionein (MT) is a cysteine-rich, low-molecular-weight protein that can bind to cadmium ions and reduce their toxicity to plants. In this study, we cloned the
PaMT3-1
gene encoding an unstable ...protein of 63 amino acids from the cadmium hyperaccumulator
Phytolacca americana
. The gene was inserted into a plant expression vector and introduced into tobacco plants. The cadmium content of the transgenic plants was measured after treatment with 100 mM CdCl
2
for 7 days. Transgenic and wild-type roots had similar cadmium contents, whereas the cadmium content of transgenic leaves was 66.28–78.70% of the wild type. The transport coefficient of cadmium in transgenic plants was decreased by 23.31–35.52% relative to the wild type. According to various physiological indexes, including malondialdehyde content, relative electrolyte leakage, root activity, and soluble sugar content, the transgenic plants performed better than the wild type. The
PaMT3-1
gene can significantly improve plant resistance to cadmium and has potential as an important gene resource in phytoremediation. Our findings could also contribute to an understanding of complex processes and mechanisms involved in phytoremediation.
Key message
Over-expressing a metallothionein gene
PaMT3-1
from
Phytolacca americana
in tobacco plants showed enhanced cadmium tolerance that would be important gene resource for phytoremediation.
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