SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-026-4300-3
The power conversion efficiency (PCE) of organic solar cells (OSCs) has surpassed 21% with the donor polymer D18, yet its processing from non-halogenated solvents like ortho-xylene (o-XY) remains inefficient due to uncontrolled film formation kinetics. Here, we systematically synthesize D18 polymers with molecular weights ranging from 41.6 kDa to 70.9 kDa to modulate crystallization kinetics. In-situ film drying studies reveal that lower molecular weights accelerate solidification, leading to excessive aggregation, while higher molecular weights slow it, causing insufficient phase separation. A medium molecular weight (D18-M) achieves a balanced crystallization rate, promoting favorable morphology and yielding a PCE of 20.55% with L8-BO as acceptor—one of the highest reported for non-halogenated solvent-processed OSCs. Energy loss analysis indicates that although low-molecular-weight polymers exhibit higher intrinsic luminescence, the blend film's emission is governed by exciton environment, which is dictated by morphology. This work underscores the critical role of molecular weight in controlling film formation and morphology, offering a simple yet effective strategy for high-efficiency, environmentally friendly OSCs.
SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-026-4094-8
Deep-blue multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters with high efficiency, high color purity, and high brightness are critically important for next-generation OLED displays, yet remain challenging due to severe aggregation and host-guest interactions in the solid state. Herein, we report a core-encapsulating molecular design strategy in which bulky and non-conjugated peripheral groups are introduced to sterically encapsulate a blue-emitting MR core, thereby suppressing intermolecular π-π interactions without perturbing its intrinsic electronic structure. Two new emitters, DNa-BN and QNa-BN, featuring half-encapsulated and fully encapsulated MR-core architectures, respectively, were developed. Owing to its fully encapsulated structure, QNa-BN exhibits pronounced aggregation resistance at high doping concentrations, maintaining photoluminescence quantum yields exceeding 96%, radiative decay rate constants on the order of 10^8 s−1, and fast reverse intersystem crossing rates (~10^5 s−1). Consequently, sensitizer-free OLEDs based on QNa-BN deliver narrowband deep-blue emission at 458 nm with a full width at half maximum of 22 nm, CIE coordinates of (0.142, 0.085), a maximum external quantum efficiency (EQE_max) of 34.4%, and a maximum luminance exceeding 20,000 cd m−2. Furthermore, by adopting a hyperfluorescence architecture, the EQE_max is further boosted to 38.7% with significantly suppressed efficiency roll-off. This work demonstrates that steric encapsulation of the MR core provides an effective and general approach to achieving aggregation-resistant, high-efficiency, and high-brightness deep-blue MR-TADF emitters for OLED applications.