Achieving narrowband emissions with tunable colors for multiple resonance-thermally activated delayed fluorescence materials: effect of boron/nitrogen number and position.

The boron/nitrogen (B/N)-based multiple resonance-thermally activated delayed fluorescence (MR-TADF) materials with tunable colors have attracted widespread attention owing to their great potential in next-generation display, white lighting, and imaging applications. Numerous MR-TADF emitters with different B/N number and position have been reported to realize full-color narrowband emissions. To gain a better understanding of the effect of B/N number and position on the photo-electronic properties, geometric and electronic properties, Huang-Rhys factors and reorganization energies, charger transfer and absorption/emission properties were analyzed in detail to determine the structure-property relationship for the investigated molecules. The calculated results show that the molecules with para-atoms having the same electronic characteristics (para-B-π-B/para-N-π-N) exhibited smaller structural relaxations upon excitation, and the molecules with increased B/N atoms showed more obvious short-range charge transfer (SRCT) properties. Besides, the para-B-π-N and para-B-π-B/para-N-π-N substructures could reduce and enhance the donor and acceptor strengths, respectively, leading to tunable HOMO-LUMO gaps and emission colors. Such theoretical insights well rationalize the experimental results, revealing that the small reorganization energy and dominant SRCT property should be two key factors in realizing narrowband emissions of MR-TADF materials. These findings and understandings could give an in-depth insight into the structure-property relationship, providing molecular design strategies for the exploration of narrowband MR-TADF materials with tunable emission colors.

Manipulating Multiple Resonance-Charge Transfer Hybrid Proportion for Developing Red Narrowband Thermally Activated Delayed Fluorescence Materials.

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have attracted increasing attention because of their 100% exciton utilization capability and narrowband emissions. However, it remains a formidable challenge to develop such red materials. Herein, we perform a theoretical investigation on the design of red narrowband TADF materials via manipulating the MR-charge transfer (CT) hybrid proportion by regulating the types of MR cores and peripheral electron-donating units. The results indicate that the MR-CT proportion in the excited states is closely relevant to the frontier molecular orbital (FMO)/hole-electron overlap, which is mainly determined by the dihedral angle between the MR cores and the peripheral units for the MR donor-acceptor molecules. The electron-donating ability of the peripheral substituents has little influence on the FMO/hole-electron overlap. Finally, c1-a and c2-a with red narrowband emissions were revealed. These findings with rich physical insights into the structure-property relationship should provide important clues for designing red narrowband optoelectronic materials.

Multifunctional Resonance Bridge-Mediated Dynamic Modulation of Perovskite Films For Enhanced Intrinsic Stability of Photovoltaics.

The improving intrinsic stability, determining the life span of devices, is a challenging task in the industrialization of inverted perovskite solar cells. The most important prerequisite for boosting intrinsic stability is high-quality perovskite films deposition. Here, a molecule, N-(2-pyridyl)pivalamide (NPP) is utilized, as a multifunctional resonance bridge between poly(triarylamine) (PTAA) and perovskite film to regulate the perovskite film quality and promote hole extraction for enhancing the device intrinsic stability. The pyridine groups in NPP couple with the phenyl groups in PTAA through π-π stacking to improve hole extraction capacities and minimize interfacial charge recombination, and the resonance linkages (NCO) in NPP dynamically modulate the perovskite buried defects through strong PbO bonds based on the fast self-adaptive tautomerization between resonance forms (NCO and N+ CO- ). Because of the combined effect of the reduction defect density and improved energy level in the perovskite buried interfaces as well as the optimized crystal orientation in perovskite film enabled by the NPP substrate, the devices based on NPP-grown perovskite films show an efficiency approaching 20% with negligible hysteresis. More impressively, the unencapsulated device displays start-of-the-art intrinsic photostability, operating under continuous 1-sun illumination for 2373 h at 65 °C without loss of PCE.

Constructing high-performance TADF polymers from non-TADF monomers: a computational investigation.

Thermally activated delayed fluorescence (TADF) polymers excelling in simple, low-cost and large-area solution process ability have attracted tremendous attention recently, but it remains a great challenge for the design of such materials due to the lack of reliable molecular construction guidelines. Here we perform a systematic computational investigation on the construction of TADF polymers from non-TADF monomers to elucidate the effects of polymerization sites, substituent positions and substituent types. The results indicate that the polymerization of 3,6-carbazole-based monomers with different substituents is efficient to build TADF polymers due to their facile π-conjugation extendability. Especially, polymers with para-phenyl-substituted monomers are promising in light of their separated frontier molecular orbitals for small ΔEST with favorable energy levels, bipolar charge transport properties and relatively strong absorption/emission intensity, which should be highly attractive for experimental investigations. These findings and insights are important in revealing the structure-property relation of TADF polymers made from non-TADF monomers with important clues for understanding the construction mechanism and molecular design principles of TADF polymers.