Conventional Organic Molecules Research Articles

Designing Multifunctional Donor-Acceptor-Type Molecules to Passivate Surface Defects Efficiently and Enhance Charge Transfer of CsPbI2Br Perovskite for High Power Conversion Efficiency.

High-density and multitype surface defects of CsPbI2Br perovskite induce charge recombination and accumulation, hindering its device efficiency and stability. However, the surface defect types of CsPbI2Br perovskite are still unclear, and conventional organic molecules only passivate one specific defect and cannot achieve good overall passivation. Here, density functional theory is used to explore surface defect types and properties of CsPbI2Br with calculating the defect formation energy and electronic structure. Results show that the dominant deep-level defects are cationic defects (PbBr) under Br-poor conditions and anionic defects (Ii and Bri) under moderate and Br-rich conditions, originating from Pb-Pb bonding and I-I bonding. Multifunctional organic molecules containing donor and acceptor groups are used to passivate both cationic and anionic defects simultaneously. It turns out that the deep-level defects are effectively decreased by forming strong interaction of N-Pb, O-Pb, and halide-Pb bonds. Moreover, the electron and hole transfers from perovskite to molecules increase dramatically to -9.06 × 1012 and 2.60 × 1012 e/cm2 and maybe improve the efficiency of power conversion. Our findings not only reveal the surface defect properties of CsPbI2Br, but also offer an approach for designing new multifunctional passivators for perovskite solar cells with high conversion efficiency.

(Invited) Electrogenerated Radical Ions: A Platform for Extreme Reactivity with Unique Selectivity

Metal-based catalysts and reagents possess unique reactivity profiles that are inaccessible using conventional organic molecules and, consequently, occupy a privileged role in organic synthesis. We are investigating how organic radical ions–typically thought of as fleeting intermediates–can be tamed and exploited to expand the reactivity of bench-stable organic molecules. Our central hypothesis is that these organic radical ions will not only mimic the unique reactivity of metallic species but will also engender selectivity profiles inaccessible using existing synthetic tactics. Herein, we will describe two new reaction platforms enabled by electrochemically-generated persistent organic radical ions. In the first system, we report a strategy to mediate single electron transfer to substrates with reduction potentials more negative than <–3.0 V vs. SCE. In the second, we will discuss a new approach to oxidatively couple of alkenes and electron-rich nucleophiles via a metastable electrophilic intermediate.

Two‐Dimensional Metal–Organic Frameworks‐Based Grain Termination Strategy Enables High‐Efficiency Perovskite Photovoltaics with Enhanced Moisture and Thermal Stability

AbstractPerovskite degradation induced by surface defects and imperfect grain boundaries of films seriously damages the performance of perovskite solar cells (PSCs). Meanwhile, conventional organic molecules cannot maintain the long‐time passivation effects under the stimulation of external environmental factors. Here, efficient and stable grain passivation in perovskite films is realized by preparing formic acid‐functionalized 2D metal–organic frameworks (MOFs) as the terminated agent. Through robust interactions between exposed active sites and PbI2, the 2D MOFs tightly caps the surface of PbI2‐terminated perovskite grains to stabilize the perovskite phases and aids the adhesion of adjacent grains. The MOFs mainly distributed at the grain boundaries of the perovskite film is directly observed at the microscopic scale. The modified perovskite films have regular morphology, lower defect density, and superior optoelectronic properties. Benefiting from the suppressed charge recombination and faster charge extraction, a power conversion efficiency of 21.28% is achieved for the best‐performing PSC device. The unencapsulated PSCs with the MOFs modification maintain 88% and 81% of their initial efficiency after 750 h heating at 85 °C under N2 atmosphere and more than 1000 h storage in ambient environment (25 °C, RH ≈ 40%), respectively.

Polydiacetylene-enclosed near-infrared fluorescent semiconducting polymer dots for bioimaging and sensing.

Semiconducting polymer dots (P-dots) recently have emerged as a new type of ultrabright fluorescent probe with promising applications in biological imaging and detection. With the increasing desire for near-infrared (NIR) fluorescing probes for in vivo biological measurements, the currently available NIR-emitting P-dots are very limited and the leaching of the encapsulated dyes/polymers has usually been a concern. To address this challenge, we first embedded the NIR dyes into the matrix of poly[(9,9-dioctylfluorene)-co-2,1,3-benzothiadiazole-co-4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole] (PF-BT-DBT) polymer and then enclosed the doped P-dots with polydiacetylenes (PDAs) to avoid potential leakage of the entrapped NIR dyes from the P-dot matrix. These PDA-enclosed NIR-emitting P-dots not only emitted much stronger NIR fluorescence than conventional organic molecules but also exhibited enhanced photostability over CdTe quantum dots, free NIR dyes, and gold nanoclusters. We next conjugated biomolecules onto the surface of the resulting P-dots and demonstrated their capability for specific cellular labeling without any noticeable nonspecific binding. To employ this new class of material as a facile sensing platform, an easy-to-prepare test paper, obtained by soaking the paper into the PDA-enclosed NIR-emitting P-dot solution, was used to sense external stimuli such as ions, temperature, or pH, depending on the surface functionalization of PDAs. We believe these PDA-coated NIR-fluorescing P-dots will be very useful in a variety of bioimaging and analytical applications.