Dimerized Acceptors with Conjugate-Break Linker Enable Highly Efficient and Mechanically Robust Organic Solar Cells.

Designing new acceptors is critical for intrinsically stretchable organic solar cells (IS-OSCs) with high efficiency and mechanical robustness. However, nearly all stretchable polymer acceptors exhibit limited efficiency and high-performance small molecular acceptors are very brittle. In this regard, we select thienylene-alkane-thienylene (TAT) as the conjugate-break linker and synthesize four dimerized acceptors by the regulation of connecting sites and halogen substitutions. It is found that the connecting sites and halogen substitutions considerably impact the overall electronic structures, aggregation behaviors, and charge transport properties. Benefiting from the optimization of the molecular structure, the dimerized acceptor exhibits rational phase separation within the blend films, which significantly facilitates exciton dissociation while effectively suppressing charge recombination processes. Consequently, FDY-m-TAT-based rigid OSCs render the highest power conversion efficiency (PCE) of 18.07 % among reported acceptors containing conjugate-break linker. Most importantly, FDY-m-TAT-based IS-OSCs achieve high PCE (14.29 %) and remarkable stretchability (crack-onset strain [COS]=18.23 %), significantly surpassing Y6-based counterpart (PCE=12.80 % and COS=8.50 %). To sum up, these findings demonstrate that dimerized acceptors containing conjugate-break linkers have immense potential in developing highly efficient and mechanically robust OSCs.

Preparation and Characterization of Physically Activated Carbon and Its Energetic Application for All-Solid-State Supercapacitors: A Case Study.

Biomass-derived activated carbons have gained significant attention as electrode materials for supercapacitors (SCs) due to their renewability, low-cost, and ready availability. In this work, we have derived physically activated carbon from date seed biomass as symmetric electrodes and PVA/KOH has been used as a gel polymer electrolyte for all-solid-state SCs. Initially, the date seed biomass was carbonized at 600 °C (C-600) and then it was used to obtain physically activated carbon through CO2 activation at 850 °C (C-850). The SEM and TEM images of C-850 displayed its porous, flaky, and multilayer type morphologies. The fabricated electrodes from C-850 with PVA/KOH electrolytes showed the best electrochemical performances in SCs (Lu et al. Energy Environ. Sci., 2014, 7, 2160) application. Cyclic voltammetry was performed from 5 to 100 mV s-1, illustrating an electric double layer behavior. The C-850 electrode delivered a specific capacitance of 138.12 F g-1 at 5 mV s-1, whereas it retained 16 F g-1 capacitance at 100 mV s-1. Our assembled all-solid-state SCs exhibit an energy density of 9.6 Wh kg-1 with a power density of 87.86 W kg-1. The internal and charge transfer resistances of the assembled SCs were 0.54 and 17.86 Ω, respectively. These innovative findings provide a universal and KOH-free activation process for the synthesis of physically activated carbon for all solid-state SCs applications.

Alignment of Organic Conjugated Molecules for High-Performance Device Applications.

High-performance organic semiconductor materials as the electroactive components of optoelectronic devices have attracted much attention and made them ideal candidates for solution-processable, large-area, and low-cost flexible electronics. Especially, organic field-effect transistors (OFETs) based on conjugated semiconductor materials have experienced stunning progress in device performance. To make these materials economically viable, comprehensive knowledge of charge transport mechanisms is required. The alignment of organic conjugated molecules in the active layer is vital to charge transport properties of devices. The present review highlights the recent progress of processing-structure-transport correlations that allow the precise and uniform alignment of organic conjugated molecules over large areas for multiple electronic applications, including OFETs, organic thermoelectric devices (OTEs), and organic phototransistors (OPTs). Different strategies for regulating crystallinity and macroscopic orientation of conjugated molecules are introduced to correlate the molecular packing, the device performance, and charge transport anisotropy in multiple organic electronic devices.

The Role of Entropy Gains in the Exciton Separation in Organic Solar Cells.

In organic solar cells (OSCs), the lower dielectric constant of organic semiconductor material induces a strong Coulomb attraction between electron-hole pairs, which leads to a low exciton separation efficiency, especially the charge transfer (CT) state. The CT state formed at the electron-donor (D) and electron-acceptor (A) interface is regarded as an unfavorable property of organic photovoltaic devices. Since the OSC works in a nonzero temperature condition, the entropy effect would be one of the main reasons to overcome the Coulomb energy barrier and must be taken into account. In this review, the present understanding of the entropy-driven charge separation is reviewed and how factors such as the dimensionality of the organic semiconductor, energy disorder effect, the morphology of the active layer, are described, as well as how the nonequilibrium effect affects the entropy contribution in compensating the Coulomb dissociation barrier for CT exciton separation and charge generation process. The investigation of the entropy effect on exciton dissociation mechanism from both theoretical and experimental aspects is focused on, which provides pathways for understanding the underlying mechanisms of exciton separation and further enhancing the efficiency of OSCs.

Synergistic Effect of Solvent and Epitaxy on the Formation of Anisotropic Structures of P3HT and P3HT/PCBM Films.

Oriented organic semiconductor blends can confer desirable properties, such as enhanced charge transport properties and polarized light emission or absorption. A technique that is not only adapted to solution processing but also producing anisotropic conducting blend films is realized by epitaxial crystallization of blends on oriented polymer substrate. The epitaxial structure of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) on oriented polyethylene (PE) substrate is affected by the boiling point of the used solvent. The P3HT spin-coated from o-dichlorobenzene with a high boiling point on PE forms a "side-on" and "face-on" molecular chain orientation with c-axis parallel to the c-axis of PE. While the orientation of the side-on and face-on is poor when P3HT is spin-coated from chloroform with a low boiling point. The addition of PCBM does not affect the epitaxial crystallization behavior of P3HT. Moreover, the anisotropic structure of PCBM is also obtained on the PE substrate. The PE substrate efficiently increases the amount of the face-on structure and the ratio of the face-on to side-on is 7 times that on the PSS:PEDOT substrate. Anisotropic structures lead to anisotropic absorption and photoluminescence properties. The anisotropic optical properties are better for the sample spin-coated from o-dichlorobenzene with the dichroic ratio of 2. The technique of employing oriented PE film to regulate the formation of oriented conducting polymer combined with the analytical method provides guidance to the fabrication and characterization of anisotropic functional film.