On the role of asymmetric molecular geometry in high-performance organic solar cells.

Although asymmetric molecular design has been widely demonstrated effective for organic photovoltaics (OPVs), the correlation between asymmetric molecular geometry and their optoelectronic properties is still unclear. To access this issue, we have designed and synthesized several symmetric-asymmetric non-fullerene acceptors (NFAs) pairs with identical physical and optoelectronic properties. Interestingly, we found that the asymmetric NFAs universally exhibited increased open-circuit voltage compared to their symmetric counterparts, due to the reduced non-radiative charge recombination. From our molecular-dynamic simulations, the asymmetric NFA naturally exhibits more diverse molecular interaction patterns at the donor (D):acceptor (A) interface as compared to the symmetric ones, as well as higher D:A interfacial charge-transfer state energy. Moreover, it is observed that the asymmetric structure can effectively suppress triplet state formation. These advantages enable a best efficiency of 18.80%, which is one of the champion results among binary OPVs. Therefore, this work unambiguously demonstrates the unique advantage of asymmetric molecular geometry, unveils the underlying mechanism, and highlights the manipulation of D:A interface as an important consideration for future molecular design.

Hot-Electron-Induced Photochemical Properties of CdSe/ZnSe Core/Shell Quantum Dots under an Ambient Environment.

Using CdSe/ZnSe core-shell quantum dots (QDs) as a model, we systematically investigate the photochemical properties of QDs with the ZnSe shells under an ambient environment, which show almost opposite responses to either oxygen or water in comparison with CdSe/CdS core/shell QDs. While the ZnSe shells provide an efficient potential barrier for photoinduced electron transfer from the core to the surface-adsorbed oxygen, they also act as a stepping stone for hot-electron transfer directly from the ZnSe shells to oxygen. The latter process is so effective and competes favorably with ultrafast relaxation of hot electrons from the ZnSe shells to the core QDs, which can completely quench the photoluminescence (PL) with saturated adsorption of oxygen (1 bar) and initiate oxidation of the surface anion sites. Water can slowly eliminate the excess hole to neutralize the positively charged QDs, partially canceling the photochemical effects of oxygen. Alkylphosphines─through two distinctive reaction pathways with oxygen─stop the photochemical effects of oxygen and completely recover PL. With limited thickness (around two monolayers), the ZnS outer shells substantially slow down photochemical effects on CdSe/ZnSe/ZnS core/shell/shell QDs but cannot fully stop PL quenching by oxygen.

High-Performance Small Molecule Organic Solar Cells Enabled by a Symmetric-Asymmetric Alloy Acceptor with a Broad Composition Tolerance.

Using a combinatory blending strategy is demonstrated as a promising path for designing efficient organic solar cells (OSCs) by boosting the short-circuit current density and fill factor. Herein, a high-performance ternary all-small molecule OSC (all-SMOSCs) using a narrow-bandgap alloy acceptor containing symmetric and asymmetric molecules (BTP-eC9 and SSe-NIC) and a wide-bandgap small molecule donor MPhS-C2 is reported. Introducing the synthesized SSe-NIC into the MPhS-C2:BTP-eC9 host system can broaden the absorption spectrum, modulate energy offsets, and optimize the molecular packing of the host materials. After systematically optimizing the weight ratio of MPhS-C2:BTP-eC9:SSe-NIC, a champion efficiency of 18.02% is achieved. Impressively, the ternary system not only delivered a broad composition tolerance with device efficiencies over 17% throughout the whole blend ratios, but also exhibited less non-geminate recombination and energy loss, and better-light-soaking stability than the corresponding binary systems. This work promotes the development of high-performance ternary all-SMOSCs and heralds their brighter application prospects.

Morphology-maintaining synthesis of copper hydroxy phosphate@metal-organic framework composite for extraction and determination of trace mercury in rice.

A novel copper hydroxy phosphate@MOF composite DMP-Cu decorated by 2, 5-dimercapto-1, 3, 4-thiadiazol was facilely prepared and characterized. A dispersive SPE strategy using DMP-Cu as adsorbent combined with atomic fluorescence spectroscopy was developed for the selective capture of trace total mercury in rice sample. The adsorption mechanism showed that the Hg2+ removal process was fitted with pseudo second-order kinetics and the Langmuir adsorption model. The adsorbent was easy to be regenerated and the maximum adsorption capacity for the removal of Hg2+ was 249.5 mg g-1 at the optimal pH of 4. X-ray photoelectron spectroscopy and Raman spectra verified the selective and strong interaction between Hg2+ and thiol/nitrogen-containing functional groups of DMTZ on DMP-Cu. The trace total mercury in rice samples was determined with detection limit of 0.0125 ng mL-1 and relative standard deviation below 6%. The high recoveries were obtained in range of 98.8-109% for the spiked rice samples.