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Molecular engineering of high-performance non-fullerene acceptors (NFAs) is critical to enhance the power conversion efficiencies (PCEs) of bulk heterojunction organic solar cells (BHJ OSCs). In this work, density functional theory (DFT) and time-dependent DFT are employed to investigate the effects of π-bridge engineering on the photoelectric performance of high-performance NFA Y6. This π-bridge engineering principally involves (1) inserting different types of π-bridge units between the fused-ring core and the terminal unit of Y6, and then the π-bridge unit with better performance is screened for the next study, (2) inserting different numbers of screened π-bridge units between the fused-ring core and the terminal unit of Y6, and (3) modifying the side chains of the screened π-bridge unit with halogen atoms. Theoretical results predict that the selenophene π-bridge has superior properties in terms of dipole moment, exciton binding energy, and light absorption compared with other π-bridge units. In addition, studies on different numbers of selenophene π-bridges suggest that increasing the number of selenophene π-bridges has significant advantages in enhancing light absorption and electron transport capabilities for enhancing the short circuit current density (JSC). Meanwhile, the study of π-bridged side chains substituted with different halogen atoms indicates that the substitution of halogen atoms can play a significant role in reducing the exciton binding energy and raising the transferred charge amounts. The results obtained in this work are expected to be used to design new Y6 derivatives. [ABSTRACT FROM AUTHOR]

Exploring flexible dielectrics with high dielectric constant and low loss is pertinent for many applications in electronic devices. In the present work, a non-ferroelectric polymer, polyvinyl alcohol (PVA), was used to fabricate homogeneous dielectric composite films with a relatively high dielectric constant and a low dielectric loss by using 2D nano sheets (Ti 3 C 2 T x MXene) as the filler. To limit dielectric loss, SiO 2 was coated onto the surface of MXene to provide interfacial barrier effect and suppress dielectric loss. MXene@SiO 2 /PVA composite films showed lower dielectric losses at low frequencies (from 20 Hz to ~ 10 kHz) compared with MXene/PVA composite films. MXene@SiO 2 /PVA composite films with 2.5 wt% MXene loading and 5 wt% (with respect to MXene content) SiO 2 coating had a dielectric constant of 27.2 (a 292.5% rise compared to neat PVA film) and a dielectric loss of only 0.057 (a 259.6% reduction compared to MXene/PVA composite film) at 100 Hz and room temperature (RT). In addition, this SiO 2 -coated composite film had stable dielectric properties (dielectric constant and loss change from 27.2 to 29.3 and 0.057 to 0.104, respectively) in the temperature range of RT to 60 °C. This work provides a promising way to fabricate PVA-based dielectric composites with excellent dielectric properties for practical applications in electronics. [ABSTRACT FROM AUTHOR]