In this work, five PTB7-Th-based conjugated polymers (PTB7-Th, PTBSi20, PTBSi25, PTBSi33, and PTBSi100) with different contents of siloxane-terminated pentyl side chain were synthesized, and properties of corresponding blend films with narrow band gap nonfullerene IEICO-4F acceptor were extensively investigated. According to the contact angle testing, the PTB7-Th with 100% alkyl side chain and PTBSi100 100% siloxane-terminated side chain on the benzodithiophene unit showed surface energy values of 40.04 and 34.52 mJ/m2, respectively. The results demonstrate that relative to alkyl side chain in PTB7-Th, the siloxane-terminated side chain could effectively reduce the surface energy of a resulting polymer. Based on Flory–Huggins interaction parameter estimations, the miscibility between the polymer and IEICO-4F would vary in an order of PTB7-Th > PTBSi20 > PTBSi25 > PTBSi33 > PTBSi100, suggesting that siloxane-terminated side chain would afford a tunable driving force for phase separation. Transmission electron microscopy and Raman mapping could confirm large bulk domains inside the PTBSi100:IEICO-4F blend film. In polymer solar cells, the blend film of the PTBSi100 with the lowest miscibility to IEICO-4F showed an undesirable power conversion efficiency (PCE) of 8.52%, which was significantly lower than that of 11.23% for PTB7-Th, suggesting that too large phase separation driving force is not beneficial for the device performance. Side-chain random copolymers PTBSi20, PTBSi25, and PTBSi33 for fine tuning could display PCEs of 11.94, 12.61, and 11.80%, respectively, all higher than that of PTB7-Th. Our results not only reveal the big surface energy difference between the siloxane-terminated side chain and the common alkyl side chain but also provide a guideline for side chain engineering of conjugated polymer donors with tunable morphology and optimal matching with a nonfullerene acceptor.

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With the development of 5G, Internet of Things, and smart home technologies, miniaturized and compact multi-antenna systems and multiple-input multiple-output (MIMO) antenna arrays have attracted increasing attention. Reducing the coupling between antenna elements is essential to improving the performance of such MIMO antenna system. In this work, we proposed a graphene-assembled, as an alternative material rather than metal, film-based MIMO antenna array with high isolation for 5G application. The isolation of the antenna element is improved by a graphene assembly film (GAF) frequency selective surface and isolation strip. It is shown that the GAF antenna element operated at 3.5 GHz has the realized gain of 2.87 dBi. The addition of the decoupling structure improves the isolation of the MIMO antenna array to more than 10 dB and corrects the antenna radiation pattern and operating frequency. The isolation between antenna elements with an interval of 0.4λ is above 25 dB. All experimental results show that the GAF antenna and decoupling structure are efficient devices for 5G mobile communication.

Flexible electronic devices are widely used in the Internet of Things, smart home and wearable devices, especially in carriers with irregular curved surfaces. Light weight, flexible and corrosion-resistant carbon-based materials have been extensively investigated in RF electronics. However, the insufficient electrical conductivity limits their further application. In this work, a flexible and low-profile dual-band Vivaldi antenna based on highly conductive graphene-assembled films (GAF) is proposed for 5G Wi-Fi applications. The proposed GAF antenna with the profile of 0.548 mm comprises a split ring resonator and open circuit half wavelength resonator to implement the dual band-notched characteristic. The operating frequency of the flexible GAF antenna covers the Wi-Fi 6e band, 2.4–2.45 GHz and 5.15–7.1 GHz. Different conformal applications are simulated by attaching the antenna to the surface of cylinders with different radii. The measured results show that the working frequency bands and the radiation patterns of the GAF antenna are relatively stable, with a bending angle of 180°. For demonstration of practical application, the GAF antennas are conformed to a commercial router. The spectral power of the GAF antenna router is greater than the copper antenna router, which means a higher signal-to-noise ratio and a longer transmission range can be achieved. All results indicate that the proposed GAF antenna has broad application prospects in next generation Wi-Fi.

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sp2 nanocrystallited carbon films with large nanocrystallite sizes, smooth surfaces, and relative high hardness were prepared with different ion irradiation densities regulated with the substrate magnetic coil current in an electron cyclotron resonance plasma sputtering system. Their multiscale frictional behaviors were investigated with macro pin-on-disk tribo-tests and micro nanoscratch tests. The results revealed that, at an ion irradiation density of 16 mA/cm2, sp2 nanocrystallited carbon film exhibits the lowest friction coefficient and good wear resistant properties at both the macroscale and microscale. The film sliding against a Si3N4 ball under a contact pressure of 0.57 GPa exhibited a low friction coefficient of 0.09 and a long wear life at the macroscale. Furthermore, the film sliding against a diamond tip under a contact pressure of 4.9 GPa exhibited a stable low friction coefficient of 0.08 with a shallow scratch depth at the microscale. It is suggested that sp2 nanocrystallites affect the frictional behaviors in the cases described differently. At the macroscale, the contact interface via the small real contact area and the sp2 nanocrystallited transfer layer dominated the frictional behavior, while the sp2 nanocrystallited structure in the film with low shear strength and high plastic resistivity, as well as the smooth surface morphology, decided the steady low nanoscratch properties at the microscale. These findings expand multiscale tribological applications of sp2 nanocrystallited carbon films.