Linear Regulating of Polymer Acceptor Aggregation with Short Alkyl Chain Units Enhances All-Polymer Solar Cells' Efficiency.

The power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) has ascended rapidly arising from the development of polymerized small-molecule acceptor materials. However, numerous insulating long alkyl chains, which ensure the solubility of the polymer, result in inferior aggregation and charge mobility. Herein, this study proposes a facile random copolymerization strategy of two small molecule acceptor units with different lengths of alkyl side chains and synthesizes a series of polymer acceptors PYT-EHx, where x is the percentage of the short alkyl chain units. The aggregation strength and charge mobility of the acceptors rise linearly with increasing the proportion of short alkyl chain units. Thus, the PYT-EH20 reaches balanced aggregation with the star polymer donor PBDB-T, resulting in optimal morphology, fastest carrier transport, and reduced recombination and energy loss. Consequently, the PYT-EH20-based device yields a 14.8% PCE, a 16% improvement over the control PYT-EH0-based device, accompanied by an increase in open-circuit voltage (Voc ), short-circuit current density (Jsc ), and fill factor (FF). This work demonstrates that the random copolymerization strategy with short alkyl chain insertion is an effective avenue for developing high-performance polymer acceptors, which facilitates further advances in the efficiency of all-PSCs.

Direct Observation of the Charge Transfer States from a Non-Fullerene Organic Solar Cell with a Small Driving Force.

For organic solar cells (OSCs), the charge generation mechanism and the recombination loss are heavily linked with charge transfer states (CTS). Measuring the energy of CTS (ECT) by the most widely used technique, however, has become challenging for the non-fullerene-based OSCs with a small driving force, resulting in difficulty in the understanding of OSC physics. Herein, we present a study of the PM6:Y6 bulk heterojunction. It is demonstrated that electro-absorption can not only reveal the dipolar nature of Y6 but also resolve the morphology-dependent absorption signal of CTS in the sub-bandgap region. The device with the optimum blending weight ratio shows an ECT of 1.27 eV, which is confirmed by independent measurements. Because of the charge transfer characteristics of Y6, the charge generation at PM6:Y6 interfaces occurs efficiently under a small but non-negligible driving force of 0.14 eV, and the total recombination loss is as low as 0.43 eV.

Biomimetic Structural Color Films with a Bilayer Inverse Heterostructure for Anticounterfeiting Applications.

The unique brilliant and angle-independent structural colors of morpho butterfly wings were derived from the multilayer interference, diffraction, and scattering of light with a composite structure including ordered and quasiamorphous arrays. Inspired by the biological heterostructure of ordered and quasiamorphous arrays in the wings, a bilayer inverse heterostructure (BLIHS) containing ordered array layers inverse structure (OALIS) and quasiamorphous array layers inverse structure (Q-AALIS) of polyvinylidene fluoride were successfully prepared through the template method. The BLIHS films selectively displayed iridescent structural color derived from Bragg diffraction of OALIS, whereas the color states transform to noniridescent color because of Q-AALIS just by rotating the sample. Furthermore, the patterning process could be realized by using the spray-coating method on the BILIS films as quasiamorphous array layers. By virtue of this novel photonic structure, the switch between hiding and displaying patterns could be easily realized by changing the viewing angles, and the as-prepared films exhibited inherent excellent durability, which is crucial to their potential for practical applications as anticounterfeiting materials.

Synthesis of Novel Reactive Disperse Silicon-Containing Dyes and Their Coloring Properties on Silicone Rubbers.

Novel red and purple reactive disperse silicon-containing dyes were designed and synthesized using p-nitroaniline and 6-bromo-2,4-dinitro-aniline as diazonium components, the first condensation product of cyanuric chloride and 3-(N,N-diethyl)amino-aniline as coupling component, and 3-aminopropylmethoxydimethylsilane, 3-aminopropylmethyldimethoxysilane, and 3-aminopropyltrimethoxysilane as silicone reactive agents. These dyes were characterized by UV-Vis, ¹H-NMR, FT-IR, and MS. The obtained reactive disperse silicon-containing dyes were used to color silicone rubbers and the color fastness of the dyes were evaluated. The dry/wet rubbing and washing fastnesses of these dyes all reached 4-5 grade and the sublimation fastness was also above 4 grade, indicating outstanding performance in terms of color fastness. Such colored silicone rubbers showed bright and rich colors without affecting its static mechanical properties.