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Vacuum Coating—A Comprehensive Guide to Electron-Beam Evaporation Coating and Equipment Maintenance
Under high vacuum, the filament of the electron gun is heated to emit thermally emitted electrons, which are then accelerated by the anode to acquire substantial kinetic energy and bombard the evaporation material. The conversion of this kinetic energy into heat causes the evaporation material to be heated and vaporized, thereby realizing electron-beam evaporation deposition. The electron-beam evaporation source consists of a thermionic cathode that emits electrons, an electron-accelerating electrode, and the coating material serving as the anode. The energy of the electron beam can be highly concentrated, enabling localized high temperatures in the coating material and thus promoting its evaporation. By adjusting the power of the electron beam, the evaporation rate of the coating material can be conveniently controlled, which is particularly advantageous for high-melting-point metals and high-purity metallic and compound materials.
2022
11-23
Submitted to Advanced Materials: Molecular Crystallinity and Twin Carrier Transport in Non-Fullerene Organic Photovoltaic Cells by Liu Feng, Gao Ke of Shandong University, and Others
Professor Feng Liu and Professor Yongming Zhang of Shanghai Jiao Tong University, Professor Ke Gao of Shandong University, and Professor Alex Jen of City University of Hong Kong have collaborated on a detailed study of the structural details and arrangement patterns of classic ITIC-type non-fullerene acceptor molecules across the “single crystal–pure film–blended film” hierarchy. Their work reveals a strong spontaneous carrier-generation phenomenon in non-fullerene acceptors (NFAs) and identifies two primary pathways for charge generation in organic thin-film photovoltaic cells: (1) intrinsic carrier generation within the NFA phase, and (2) exciton dissociation at the donor–acceptor interface to produce free carriers. This dual-channel mechanism represents another significant advantage of NFAs beyond their superior light absorption and favorable energy-level alignment, collectively underpinning the success of NFA materials in organic photovoltaics. Figure 1. (a) Morphology and (b) photophysical pathway diagram of blended films in non-fullerene organic solar cells. The paper begins with a comparative analysis of the crystal structures of three NFA molecules: ITIC, 4TIC, and 6TIC. It finds that π–π stacking interactions and side-chain interactions are the two dominant factors governing the crystal structure of NFAs. The volume ratio of the side chains to the molecular backbone is a key determinant of spatial confinement. For ITIC, this ratio is 1.059, resulting in a two-dimensional brickwork packing where the backbone forms layered structures through terminal π–π interactions, while the side chains aggregate in the interlayer voids. As the backbone length decreases, the side-chain-to-backbone volume ratio for 4TIC increases to 1.146, leading the molecule to adopt a three-dimensional web-like structure. In 4TIC, the side chains assemble in a tightly packed configuration, filling the spaces around the backbone’s π–π stacks to achieve a densely packed arrangement balanced by multiple intermolecular forces. When the backbone is further elongated, the side-chain-to-backbone volume ratio for 6TIC drops to 1.030, prompting the molecule to form a hierarchical structure. Under the influence of both side-chain interactions and π–π stacking, 6TIC first self-assembles into a zigzag pattern; these units then link via hydrogen bonds to form two-dimensional assembly layers, which in turn stack in a three-dimensional architecture through intercalation of blue- and yellow-colored conformational molecules. Figure 2. Crystal structures of the three molecules. Next, the authors employ grazing-incidence wide-angle X-ray scattering (GIWAXS) to analyze the crystalline structures of NFA molecules in both pure and blended films. By comparing pure films prepared under different processing conditions—specifically, with or without the DIO additive—and combining GIWAXS experiments with computational simulations, they investigate the sequence of molecular assembly in NFAs. The study shows that molecules with higher energy density, such as ITIC and 4TIC, directly form crystalline structures, though variations in processing conditions lead to differences in crystallinity and order; in contrast, for the hierarchically assembled 6TIC acceptor, the molecule first forms two-dimensional layered structures and, under the influence of the DIO additive, further develops a three-dimensional crystalline structure. These differences in intermolecular forces determine how well NFA molecules maintain their crystalline phases in blended films. In blended films, the presence of donor polymers and acceptor molecules generally reduces the crystallinity of NFAs; however, the use of the DIO additive can enhance NFA crystallinity, and strong intermolecular interactions help preserve the crystalline morphology. Notably, even when prepared under DIO conditions, 6TIC maintains its two-dimensional layered packing due to its hierarchical assembly. Figure 3. GIWAXS patterns of pure films and the assembly process of molecular crystallization in pure films. Furthermore, ultrafast transient absorption spectroscopy (TA) is used to probe the photophysical properties of blended films, with long-wavelength laser excitation directed specifically at the NFA acceptor. In the TA spectrum of an ITIC pure film, an excited-state signal at 955 nm and a polaron signal at 1335 nm can be observed. In pure films prepared under DIO conditions, excitons convert more rapidly into polarons, indicating that the crystalline phase of NFAs harbors a spontaneous exciton-dissociation pathway that does not rely on exciton dissociation at the donor–acceptor interface—a novel mechanism for charge carrier formation. Similar results are also seen in the TA spectra of 4TIC and 6TIC pure films. Moreover, the decay curve of polarons in 6TIC pure films exhibits a broad plateau (with a lifetime exceeding 1000 ps), suggesting that 6TIC’s two-dimensional structure is conducive to accommodating separated polarons. In the TA spectra of blended films, polarons can be detected as early as 0 fs, alongside evidence of hole transfer from the NFA acceptor to the donor material. In DIO-prepared blended films, the yield of polarons increases and the rate of hole transfer accelerates. Quantitative comparisons reveal that, at 0 fs, the interfacial polaron yield in blended films is comparable to the spontaneous polaron yield, underscoring the importance of both charge-generation pathways in non-fullerene donor–acceptor blended films. Device data further indicate that broadening the absorption range of NFA materials enhances device current, while increasing CT-state energy and reducing CT-state density helps minimize non-radiative losses and improve open-circuit voltage. Together with the spontaneous carrier-generation pathway, these findings provide a more comprehensive explanation of the photoelectric conversion process in organic photovoltaics. Figure 4. Ultrafast spectroscopy of blended films, polaron lifetimes, polaron yields, and a schematic illustration of the photophysical processes involved. Figure 5. Fitting of the CT state in blended films, along with EL spectra of pure and blended films. In summary, this work provides an in-depth exploration of the crystalline structures and self-assembly processes of NFA molecules, analyzes the influence of intermolecular forces on orderly molecular assembly, establishes a systematic methodology for studying NFA crystals and thin-film morphologies, and elucidates the dual-channel charge-generation mechanism in non-fullerene organic photovoltaic cells. These findings offer new insights into the structure of organic photovoltaic materials and their photoelectric conversion processes, thereby facilitating the development of novel materials.
03-21
Xing Jun et al., Nat. Commun.: Molecular Engineering of High-Efficiency White Perovskite LEDs
Low-dimensional hybrid perovskites exhibit outstanding performance as white-light emitters. Broadband white-light emission originates from self-trapped excitons (STEs). However, the formation mechanism of STEs in perovskites remains poorly understood, and the synthesis of new low-dimensional white perovskites has thus relied primarily on screening large libraries of organic intercalants rather than on rational molecular design.
2021
08-16
Chen Qi & Zhou Huanping, Science: Breakthrough! Over 24% Efficiency! Highly Reproducible and Durable Perovskite Solar Cells
Solution processing of semiconductors holds great promise for the high-throughput production of cost-effective electronic and optoelectronic devices. Although hybrid perovskites demonstrate significant potential in a wide range of device applications, challenges remain in developing high-quality materials that simultaneously enhance process reproducibility and scalability. Qi Chen of Beijing Institute of Technology and Huanping Zhou of Peking University have reported a liquid-medium annealing (LMA) technique that establishes a robust chemical environment and a uniform heating field to regulate crystal growth across the entire thin film.
07-30
Chen Qi, Joule: 23.9% Efficiency! Dual Back-Contact Interface Layer for High-Efficiency and Stable Perovskite Solar Cells
As perovskite solar cells (PSCs) move toward practical applications, both high efficiency and long-term stability are essential, with the interfaces playing a crucial role. Researchers led by Qi Chen at Beijing Institute of Technology have developed interface layers and electrode buffer layers tailored for the hole-transport layer (HTL), achieving a dual rear-field (SEB) architecture at the two relevant interfaces.
07-12
Chen Jiangzhao et al.: 16.75% Efficiency! Methylammonium-Free Two-Dimensional DJ-Phase Perovskite Solar Cells
Recently, the research team led by Researcher Chen Jiangzhao from the School of Optoelectronic Engineering at Chongqing University published an article titled “Interfacial gradient energy band alignment modulation via ion exchange reaction toward efficient and stable methylammonium-free Dion-Ja” in the internationally renowned academic journal Journal of Power Sources (a TOP-tier journal).
07-06
Zhang Xiaodan, ACS Energy Letters: Record-breaking! Perovskite solar cell with 23.8% efficiency
SnO2 is widely used as the electron-transport layer in perovskite solar cells; however, SnO2 thin films typically contain a large number of detrimental defect states and exhibit poor band alignment with the perovskite material, leading to losses in the open-circuit voltage of the device. Researchers at Nankai University, including Xiaodan Zhang, have reported that incorporating CoCl2·6H2O into the SnO2 film can effectively enhance band alignment and improve charge extraction, thereby boosting the overall performance of the solar cell.
05-18
Cai Zhihao et al. AM: Over 10% Efficiency! Highly Stable Blue Perovskite Light-Emitting Diodes
Although numerous studies have been conducted to tune the quasi-2D perovskite composition in perovskite light-emitting diodes (PeLEDs) to enhance their electroluminescence, few reports have addressed strategies for enhancing energy transfer among the quasi-2D perovskite layers in the thin film—a critical factor for achieving high-performance PeLEDs.
2020
11-24
Lu Xinhui & Fang Guojia Matter: GIWAXS Reveals the Influence of Halogens on Crystallization and Phase Evolution in Inorganic Perovskite Thin Films
All-inorganic perovskite solar cells (PSCs) have garnered increasing attention due to their outstanding thermal stability, which is attributed to their potentially superior thermal robustness. However, the film-forming processes and phase-transition mechanisms of CsPbX3 thin films with different halide compositions (I, Br, Cl) remain poorly understood. Moreover, there is currently no consensus on the role of halide elements in the phase transitions and crystal-growth kinetics of all-inorganic perovskites. Researchers led by Xin-Hui Lu at the Chinese University of Hong Kong and Guo-Jia Fang at Wuhan University have employed state-of-the-art in situ grazing-incidence wide-angle X-ray scattering to investigate the real-time crystalline and phase evolution of all-inorganic perovskite thin films.
11-16
Dr. Pradhan: Synthesis, Optical Properties, and Applications of Perovskite Nanocrystal Heterostructures
Heterostructures often exhibit synergistic effects that exceed the sum of their individual components. Currently, heterostructures involving metal nanoparticles and chalcogenide semiconductor nanocrystals have been extensively studied; however, research on heterostructures based on perovskite nanocrystals, which have experienced explosive growth in recent years, remains relatively limited. A primary reason for this is the extremely low formation energy of perovskite nanocrystals and their remarkably rapid growth kinetics, which pose significant challenges to the synthesis of well-defined heterostructures.
10-09
