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Controlling triplet states is crucial to improve the efficiency and lifetime of organic room temperature phosphorescence (ORTP). Although the intrinsic factors from intramolecular radiative and non-radiative decay have been intensively investigated, the extrinsic factors that affect triplet exciton quenching are rarely reported. Diffusion to the defect sites inside the crystal or at the crystal surface may bring about quenching of triplet exciton. Here, the phosphorescence lifetime is found to have a negative correlation with the triplet exciton diffusion coefficient based on the density functional theory (DFT)/time-dependent density functional theory (TD-DFT) calculations on a series of ORTP materials. For systems with a weak charge transfer (CT) characteristic, close π–π stacking will lead to strong triplet coupling and fast triplet exciton diffusion in most cases, which is detrimental to the phosphorescence lifetime. Notably, for intramolcular donor–acceptor (D–A) type systems with a CT characteristic, intermolecular D–A stacking results in ultra-small triplet coupling, thus contributing to slow triplet diffusion and long phosphorescence lifetime. These findings shed some light on molecular design toward high-efficiency long persistent ORTP. [ABSTRACT FROM AUTHOR]

Outstanding charge transport in molecular crystals is of great importance in modern electronics and optoelectronics. The widely adopted strategies to enhance charge transport, such as restraining intermolecular vibration, are mostly limited to organic molecules, which are nearly inoperative in 2D inorganic molecular crystals currently. In this contribution, charge transport in 2D inorganic molecular crystals is improved by integrating charge‐delocalized Se8 rings as building blocks, where the delocalized electrons on Se8 rings lift the intermolecular orbitals overlap, offering efficient charge transfer channels. Besides, α‐Se flakes composed of charge‐delocalized Se8 rings possess small exciton binding energy. Benefitting from these, α‐Se flake exhibits excellent photodetection performance with an ultrafast response rate (~5 μs) and a high detectivity of 1.08 × 1011 Jones. These findings contribute to a deeper understanding of the charge transport of 2D inorganic molecular crystals composed of electron‐delocalized inorganic molecules and pave the way for their potential application in optoelectronics. [ABSTRACT FROM AUTHOR]

A new acceptor-donor-acceptor-structured nonfullerene acceptor ITCC (3,9-bis(4-(1,1-dicyanomethylene)-3-methylene-2-oxo-cyclopenta[b]thiophen)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d':2,3-d']-s-indaceno[1,2-b:5,6-b']-dithiophene) is designed and synthesized via simple end-group modification. ITCC shows improved electron-transport properties and a high-lying lowest unoccupied molecular orbital level. A power conversion efficiency of 11.4% with an impressive V OC of over 1 V is recorded in photovoltaic devices, suggesting that ITCC has great potential for applications in tandem organic solar cells.

Compared to inorganic and perovskite counterparts, organic solar cells (OSCs) suffer from much more severe nonradiative energy loss due to the nongeminate recombination via triplet states at the donor:acceptor interfaces. To suppress the triplet recombination in OSCs, how to optimize the interfacial energetic landscape is very crucial. Here, we find that the lowest spin-triplet interfacial charge transfer state (TCT1) can be simultaneously hybridized with multiple local-excitation (LE) triplet states below the photovoltaic gap in the state-of-the-art OSCs based on A–D–A acceptors. More importantly, when the TCT1 state is close to the upper side of the LE triplet manifold, the hybridization will result in considerable energetic inversion between the singlet and triplet charge-transfer states. This is beneficial to destabilize the TCT1 state at close donor:acceptor separation and suppress the back charge transfer to the LE triplet states. Our work sheds light on molecular design towards reducing the triplet recombination under low driving force for higher-efficiency OSCs. [ABSTRACT FROM AUTHOR]

The blend nanomorphology of electron‐donor (D) and ‐acceptor (A) materials is of vital importance to achieving highly efficient organic solar cells. Exogenous additives especially aromatic additives are always needed to further optimize the nanomorphology of blend films, which is hardly compatible with industrial manufacture. Herein, we proposed a unique approach to meticulously modulate the aggregation behavior of NFAs in both crystal and thin film nanomorphology via self‐regulation effect. Nonfullerene acceptor Z9 was designed and synthesized by tethering phenyl groups on the inner side chains of the Y6 backbone. Compared with Y6, the tethered phenyl groups participated in the molecular aggregation via the π–π stacking of phenyl‐phenyl and phenyl‐2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (IC‐2F) groups, which induced 3D charge transport with phenyl‐mediated super‐exchange electron coupling. Moreover, ordered molecular packing with suitable phase separation was observed in Z9‐based blend films. High power conversion efficiencies (PCEs) of 19.0 % (certified PCE of 18.6 %) for Z9‐based devices were achieved without additives, indicating the great potential of the self‐regulation strategy in NFA design. [ABSTRACT FROM AUTHOR]