Pengcheng Jiang

Abstract Multiresonance thermally activated delayed fluorescence (MR‐TADF) emitters manifest great potential for organic light‐emitting diodes (OLEDs) due to their high exciton‐utilization efficiency and narrowband emission. Nonetheless, their tendency toward self‐quenching caused by strong interchromophore interactions would induce doping sensitivity and deteriorate the device performances, and effective strategy to construct quenching‐resistant emitters without sacrifycing color purity is still to be developed. By segregating the planar MR‐TADF skeleton using two bulky carbazolyl units, herein a highly emissive molecule with enhanced quenching resistance is reported. The steric effect largely removes the formation of detrimental excimers/aggregates, and boosts the performance of the corresponding devices with a maximum external quantum efficiency (EQE max ) up to 40.0% and full width at half maximum (FWHM) of 25 nm, representative of the only example of single OLED that can concurrently achieve narrow bandwidth and high EL efficiency surpassing 40% to date. Even at doping ratio of 30 wt%, the EQE max is retained to be 33.3% with nearly unchanged emission spectrum. This work provides a viable approach to realize doping‐insensitive MR‐TADF devices with extreme EL efficiency and color purity for high‐end OLED displays.

Abstract Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) offers an exceptional solution for narrowband organic light‐emitting diode devices in terms of color purity and luminescence efficiency, while the development of new MR skeleton remains an exigent task. It is hereby demonstrated that a simple modification of the B (boron)−N (nitrogen) framework by sp 3 ‐carbon insertion will significantly bathochromic shift the short‐range charge‐transfer emission, boost the reverse intersystem crossing process, and improve the device performances. The bis(acridan)phenylene‐based skeleton developed in this contribution presents a non‐planar conformation with functional sites to facilely introduce isolating units, deriving two luminophores with quantum yields approaching 90% in film state and narrowband emission. Corresponding green‐emissive devices realize superior performances compared to the planar carbazolyl‐based MR‐TADF analogs, featuring a maximum external quantum efficiency (EQE max ) up to 28.2% and small efficiency roll‐off without the involvement of any sensitizing host.

The performance of polymer solar cells (PSCs) is commonly improved using additives or annealing treatment. However, these processes are accompanied by disadvantages, including poor reproducibility and stability. Herein, a molecular design strategy is proposed to obtain additive- and annealing-free PSCs. IDTOT2F containing two alkoxyl side chains at the central unit of the nonfullerene acceptor IDTT2F was developed. This molecular design results in excellent solubility in solutions, ordered molecular packing in films, slightly elevated energy levels, and a higher film absorption coefficient. Compared with its counterpart IDTT2F, its improved solubility provides an active layer with better morphology, its ordered molecular packing enhances the charge mobility in blend films, and its slightly elevated energy level furnishes a higher open-circuit voltage of devices. As a result, IDTOT2F-based devices display a maximum power conversion efficiency of 12.79%, which is one of the highest values reported for a PSC fabricated without any extra treatment.

ConspectusOrganic solar cells (OSCs) have garnered significant attention in academic and industrial circles due to their advantages such as lightweight, excellent bending performance, and the ability to be fabricated into semitransparent devices. Since the proposal of the bulk heterojunction concept by Heeger et al. in 1995, conjugated polymer/fullerene pairs have gradually emerged as the optimal choice for active layer materials in OSCs. Fullerene derivatives were preferred as electron acceptors in OSCs because of their high electron mobility. However, due to limitations such as insufficient light absorption, limited derivative potential, and poor energy level tunability, the power conversion efficiency (PCE) of OSCs based on fullerene derivatives has encountered a bottleneck of approximately 12%, despite the continuous updates in polymer donor materials over nearly two decades of development, leading to a gradual decline in their importance. By contrast, nonfullerene electron acceptors (NFAs) have gradually gained dominance in this field since first appearing in 2015, thanks to their advantages of tunable absorption spectrum, adjustable energy levels, and modifiable chemical structure. Among nonfullerene acceptors, fused-ring electron acceptors (FREAs) such as ITIC and Y6 have achieved significant progress, boosting the PCE of OSCs to 20%. This milestone achievement indicates the potential of their commercial applications. However, the synthesis process of FREA is complex and often constrained by low-yield ring-closure reactions, resulting in high costs.The molecular backbone of nonfused ring electron acceptors (NFREAs) is composed of single bonds, which enables the adoption of modular synthesis mainly via Stille (based on organotin reactant) and/or Suzuki (based on organoboron reactant) coupling or C–H activation (without prefunctionalization) and avoids low-yield ring-closing reactions, thus making them a potential alternative to fused-ring acceptors. To achieve a planar molecular backbone and minimize energy loss due to conformational rotation, our team innovatively used intramolecular noncovalent interactions as a replacement for traditional covalent bonds. Furthermore, to address the issues of poor solubility and excessive aggregation during film formation for NFREAs, we strategically introduced sterically hindered side groups, such as 2,6-bis(alkyloxy)phenyl and diphenylamino, into the molecular design, effectively mitigating these problems. These innovative design concepts have significantly advanced the development of high-performance NFREAs and have garnered increasing attention from the research community. The PCEs of OSCs based on NFREAs have significantly improved from less than 10% to close to 20% since their initial discovery. By optimizing the device fabrication process, we have achieved a PCE of over 19%, which is comparable to that of FREAs. This article will delve into the evolution and latest research progress of NFREAs, aiming to provide valuable insights and guidance for the design of cost-effective and high-performance NFREA materials.

A nonfullerene acceptor, IDTT-OB, employing indacenodithieno[3,2-b]thiophene (IDTT) decorated with asymmetric substituents as the core, is designedly prepared. In comparison with the analogue IDT-OB, extending the five-heterocyclic indacenodithiophene (IDT) core to seven-heterocyclic fused ring endows IDTT-OB with more broad absorption and elevated highest occupied molecular orbital energy level. In addition, IDTT-OB shows a more intense molecular packing and a higher crystalline behavior with a strong face-on orientation in the neat film and the PBDB-T:IDTT-OB blend film. Furthermore, an ideal nanomorphology with a domain size of 19 nm can be obtained, which is in favor of exciton diffusion and charge separation. Accordingly, PBDB-T:IDTT-OB-based polymer solar cells demonstrate a maximum power conversion efficiency (PCEmax) of 11.19% with an impressive fill factor of 0.74, comparable to the state-of-the-art acceptors with similar molecular backbones. More importantly, IDTT-OB-based devices show good tolerance to the film thickness, which maintain a high PCE of 10.20% with a 250 nm thick active layer, demonstrating that the asymmetric acceptor is profound for fabricating high-efficiency thick-film nonfullerene solar cells.