Impact of Electrostatic Interaction on Bulk Morphology in Efficient Donor–Acceptor Photovoltaic Blends

Double Asymmetric Core Optimizes Crystal Packing to Enable Selenophene-based Acceptor with Over 18 % Efficiency in Binary Organic Solar Cells

Side-chain tailoring is a promising method to optimize the performance of organic solar cells (OSCs). However, asymmetric alkyl chain-based small molecular acceptors (SMAs) are still difficult to afford. Herein, we adopted a novel asymmetric n-nonyl/undecyl substitution strategy and synthesized two A-D₁ A'D₂ -A double asymmetric isomeric SMAs with asymmetric selenophene-based central core for OSCs. Crystallographic analysis indicates that AYT9Se11-Cl forms a more compact and order intermolecular packing compared to AYT11Se9-Cl, which contributed to higher electron mobility in neat AYT9Se11-Cl film. Moreover, the PM6 : AYT9Se11-Cl blend film shows a better morphology with appropriate phase separation and distinct face-on orientation than PM6 : AYT11Se9-Cl. The OSCs with PM6 : AYT9Se11-Cl obtain a superior PCE of 18.12 % compared to PM6 : AYT11Se9-Cl (17.52 %), which is the best efficiency for the selenium-incorporated SMAs in binary BHJ OSCs. Our findings elucidate that the promising double asymmetric strategy with isomeric alkyl chains precisely modulates the crystal packing and enhances the photovoltaic efficiency of selenophene-incorporated SMAs.

CO2 Induces Symmetry Breaking in Layered Dipeptide Crystals

Control of symmetry breaking of materials provides large opportunities to regulate their properties and functions. Herein, we report breaking the symmetry of layered dipeptide crystals by utilizing CO₂ to induce the adjacent monomolecular layers to stack from the opposite to the same direction. The role of CO₂ is to cover the interlayer interaction sites and force the dipeptides to adsorb at asymmetric positions. Further, the dipeptide crystals exhibit far superior piezoelectricity after symmetry breaking and the piezoelectric voltage generated from the dipeptide-based generators becomes more than 500 % higher than before. This work reveals a potential route to engineer structures and properties of layered materials and provides a deep insight into the control of non-covalent interactions.

Tetrathiafulvalene-Benzothiadiazole: A Metal-Free Photocatalyst for Hydrogen Production

In this work, a series of hybrid tetrathiafulvalene-benzothiadiazole (TTF-BTD) are designed and applied as a metal-free photocatalyst for hydrogen production, particularly under visible light irradiation. Density functional theory calculations are used to shed light on the photophysical properties observed in the various TTF-BTD derivatives and investigated by the obtained data. Because band gap engineering has normally been used as an effective approach, we studied the effect of the various functional groups on the band gap to set a favorable band alignment with photocatalysts. An increase in highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels is observed in the order CH₃ < Br < CF₃ < COOMe < CN. The results discover that COOMe-TTF-CN-BTD can have a clear photocatalytic potential in the hydrogen production for specific applications. Our experimental and theoretical studies reveal that the CN-withdrawing group increases the reduction potential of the conduction band; meanwhile, COOMe decreases the reduction potential of the valance band. Moreover, we demonstrate that H₂O reduction and oxidation reaction energies are both located inside the COOMe-TTF-CN-BTD band gap that enables an enhanced photocatalytic hydrogen evolution rate of 122 μmol h^-1 g^-1 under visible light. The efficiency of the COOMe-TTF-CN-BTD photocatalyst is also described in terms of medium pH and the nature of the sacrificial agent, where the maximum hydrogen production efficiency is observed at high pH. The findings point to a means of efficient production of hydrogen that can be directly achieved under visible light irradiation without any modifications.