by Changyong Cao,
Recent advances in the development of stretchable supercapacitors from low‐dimensional nanomaterials are reviewed, with an emphasis on the aspects of electrode materials, design strategies, and fabrication and performance of devices. The challenges and prospective of the stretchable supercapacitors are also discussed, providing fundamental insight and offering useful guidelines for future design of new high‐performance stretchable energy devices for wearable and medical applications.
Supercapacitors (SCs) have shown great potential for mobile energy storage technology owing to their long‐term durability, electrochemical stability, structural simplicity, as well as exceptional power density without much compromise in the energy density and cycle life parameters. As a result, stretchable SC devices have been incorporated in a variety of emerging electronics applications ranging from wearable electronic textiles to microrobots to integrated energy systems. In this review, the recent progress and achievements in the field of stretchable SCs enabled by low‐dimensional nanomaterials such as polypyrrole, carbon nanotubes, and graphene are presented. First, the three major categories of stretchable supercapacitors are discussed: double‐layer supercapacitors, pseudo‐supercapacitors, and hybrid supercapacitors. Then, the representative progress in developing stretchable electrodes with low‐dimensional (0D, 1D, and 2D) nanomaterials is described. Next, the design strategies enabling the stretchability of the devices, including the wavy‐shape design, wire‐shape design, textile‐shape design, kirigami‐shape design, origami‐shape design, and serpentine bridge‐island design are emphasized, with the aim of improving the electrochemical performance under the complex stretchability conditions that may be encountered in practical applications. Finally, the newest developments, major challenges, and outlook in the field of stretchable SC development and manufacturing are discussed.
Patrick W. K.
A novel cryogenic process has universal applicability to prepare mixed perovskite films. Excellent film quality and consequently promising device performance result from decoupling of nucleation and crystallization phases during the formation of perovskites. The cryogenic temperature suppresses premature reactions of the precursors and prevents premature coalescence of nuclei into large crystallites, enabling uniform film formation following the blow‐drying and annealing processes.
A cryogenic process is introduced to control the crystallization of perovskite layers, eliminating the need for the use of environmentally harmful antisolvents. This process enables decoupling of the nucleation and the crystallization phases by inhibiting chemical reactions in as‐cast precursor films rapidly cooled down by immersion in liquid nitrogen. The cooling is followed by blow‐drying with nitrogen gas, which induces uniform precipitation of precursors due to the supersaturation of precursors in the residual solvents at very low temperature, while at the same time enhancing the evaporation of the residual solvents and preventing the ordered precursors/perovskite from redissolving into the residual solvents. Using the proposed techniques, the crystallization process can be initiated after the formation of a uniform precursor seed layer. The process is generally applicable to improve the performance of solar cells using perovskite films with different compositions, as demonstrated on three different types of mixed halide perovskites. A champion power conversion efficiency (PCE) of 21.4% with open‐circuit voltage (VOC) = 1.14 V, short‐circuit current density ( JSC) = 23.5 mA cm−2, and fill factor (FF) = 0.80 is achieved using the proposed cryogenic process.
Understanding how excess lead iodide precursor improves halide perovskite solar cell performance
Understanding how excess lead iodide precursor improves halide perovskite solar cell performance, Published online: 17 August 2018; doi:10.1038/s41467-018-05583-w
Excess lead iodide in the mixed halide perovskites solar cells leads to high device performance but its origin remains elusive. Here Park et al. unveil the underlying microscopic mechanism to be promoting the oriented growth of the perovskites crystals and reducing the defect concentration.
Due to its super thermal stability, inorganic CsPbI2Br perovskite has attracted more and more attention in the field of photovoltaic application. However, its device performance, as reported to date, is greatly challenged in preparing CsPbI2Br films with both sufficient absorbance and high quality. Herein, crystallization engineering is applied in producing solution-processed CsPbI2Br film to guarantee sufficient light harvesting and effective carrier extraction. Further study proves that the precursor solution temperature would largely affect the crystallization progress: (1) the nucleation step is highly related to the solubility of precursor in a specific solvent or solvents at elevated temperatures; (2) the crystal growth rate is highly related to the solvent evaporation rate. To obtain thick film with larger crystalline grain size, the precursor solution temperature should be carefully adjusted for both suppressing the formation of too many nuclei and increasing the crystallization rate at the same time. Finally, the optimized CsPbI2Br would be obtained when the precursor solution is maintained at 100 °C, the corresponding device shows a stabilized efficiency as high as 14.81%. As far as we know, this is the highest PCE for the CsPbBrI2 perovskite based solar cells.
Herein, the correlation between crystallization and external factors (solubility and solvent evaporation rate) is conducted for solution-processed CsPbI2Br film. With moderate precursor solution temperature, homogenous, pinhole-free, large crystalline grain size and thick CsPbI2Br film was obtained, which effectively increased the light absorption, and decreased recombination loss. As a result, the optimized champion device achieved long-term stabilized PCE of 14.81%.
Utilizing mixed-cation-halide can improve stability of the formamidinium perovskite films and devices but sacrifices the photocurrent due to an increase in bandgap. Here Lee et al. introduced small amounts of 2D perovskite to obtain high efficiency and stability based on phase-pure formamidinium based perovskite.
Luminescent solar concentrator (LSC) can serve as large-area sunlight collectors, suitable for applications in building-integrated high-efficiency and low-cost photovoltaics. Inorganic perovskite quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs, due to their high quantum yields (close to 100%), possibility of tuning size and chemical composition and broad absorption spectrum and high absorption coefficient. However, despite their great potential for technological development, LSCs fabricated using colloidal perovskite QDs still face major challenges such as low optical efficiency and limited long-term stability. Here we report a large-area (~ 100 cm2) tandem LSC based on nearly reabsorption-free carbon dots (C-dots) and inorganic mixed-halide perovskite QDs spectrally-tuned for optimal solar-spectrum splitting. The as-fabricated semi-transparent device, without involving any complicated processes, exhibits an external optical efficiency of ~ 3% under sunlight illumination (100 mW/cm2), which represents a 27% enhancement in efficiency over single layer LSCs based on CsPb(BrxI1-x)3 QDs and 117% over CsPb(ClxBr1-x)3 QDs. Our work shows that the addition of C-dots can dramatically enhance the long-term durability of LSC devices based on perovskite QDs due to their excellent photostability and simultaneous absorption of ultraviolet light.
Author(s): Zhenye Li, Lei Ying, Ruihao Xie, Peng Zhu, Ning Li, Wenkai Zhong, Fei Huang, Yong Cao
In recent years, ternary blend bulk-heterojunction (BHJ) all-polymer solar cells have been gradually developed to better utilize the solar irradiance spectrum. However, power conversion efficiencies remain below 10%, mainly because of the low fill factor. Generally, the fill factor of all-polymer solar cells is limited mainly by the competition between the recombination and extraction of free charges. Here, we design advanced ternary blend all-polymer solar cells with a high fill factor of 78%, thus demonstrating how such recombination thresholds can be overcome. These results can be attributed to the high and balanced bulk charge mobility, reduced recombination, and optimized morphology, as well as the intimate mixing properties of the two donors in the photoactive layer.
J. Mater. Chem. A, 2018, 6,12574-12581 DOI: 10.1039/C8TA01195H, Paper
Zheng Tang, Jing Wang, Armantas Melianas, Yang Wu, Renee Kroon, Weiwei Li, Wei Ma, Mats R. Andersson, Zaifei Ma, Wanzhu Cai, Wolfgang Tress, Olle Inganas By manipulating the active-layer morphologies in OSCs, we achieve different open-circuit-voltages without affecting the energy of charge-transfer state. The content of this RSS Feed (c) The Royal Society of Chemistry
J. Mater. Chem. A, 2018, 6,13263-13270 DOI: 10.1039/C8TA02899K, Paper
Lin Fu, Yanan Zhang, Bohong Chang, Bo Li, Shujie Zhou, Luyuan Zhang, Longwei Yin The α-/δ-phase heterojunction induced by fluorine builds a matched band structure, exhibiting a champion PCE of 10.26% with improved stability. The content of this RSS Feed (c) The Royal Society of Chemistry
by Max Burian, Francesco Rigodanza, Nicola Demitri, Luka D?ord?evic, Silvia Marchesan, Tereza Steinhartova, Ilse Letofsky-Papst, Ivan Khalakhan, Eléonore Mourad, Stefan A. Freunberger, Heinz Amenitsch, Maurizio Prato, Zois Syrgiannis
Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency
Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency, Published online: 11 June 2018; doi:10.1038/s41563-018-0115-4
An optimized two-step deposition process allows the formation of uniform layers of metal halide perovskites on textured silicon layers, enabling tandem silicon/perovskite solar cells with improved optical design and efficiency.