Improving the short-circuit current density (Jsc) is a big challenge for gaining highly efficient nonfullerene all-small-molecule organic solar cells (NFASM-OSCs).

In this work, interactions between different host materials and a blue TADF polymer named P1 are systematically investigated. In photoluminescence, the host can have substantial impact on the photoluminescence quantum yield (PLQY) and the intensity of delayed fluorescence (ΦDF), where more than three orders of magnitude difference of ΦDF in various hosts is observed, resulting from a polarity effect of the host material and energy transfer. Additionally, an intermolecular charge-transfer (CT) emission with pronounced TADF characteristics is observed between P1 and 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine (PO-T2T), with a singlet-triplet splitting of 7 meV. It is noted that the contribution of harvested triplets in monochrome organic light-emitting diodes (OLEDs) correlates with ΦDF. For devices based on intermolecular CT-emission, the harvested triplets contribute ~90% to the internal quantum efficiency. The results demonstrate the vital importance of host materials on improving the PLQY and sensitizing ΦDF of TADF polymers for efficient devices. Solution-processed polychrome OLEDs with a color close to a white emission are presented, with the emission of intramolecular (P1) and intermolecular TADF (PO-T2T:P1).

Solution-processed organic light-emitting diodes (OLEDs) are much preferred for the manufacture of lowtemperature, low-cost, large-area, and flexible lighting and displaying devices. However, these devices with high external quantum efficiency are still limited, especially for blue ones. In addition, the molecular configurations of emitters are usually complicated, indicative of high costs. In this study, two simplestructured thermally activated delayed fluorescent emitters M1 and its polymer P1 were synthesized with acridine as a donor and benzophenone as an acceptor. Solution-processed OLEDs were prepared based on M1 and P1 as doped light-emitting layer, and M1-based doped device could achieve maximum external quantum efficiency of up to 20.6% with blue-light emission.

Three luminogens were designed and synthesied by integrating TPE with hole-transporting carbazole (Cz) and/or electron-transporting 1,2-diphenyl-1H-benzimidazole (PBi), and the bare tetraphenylethene and another donor−acceptor (D−A) compound of aggregation-caused quenching (ACQ)...

Materials exhibiting thermally activated delayed fluorescence (TADF) have been extensively explored in the last decade. These emitters have great potential of being used in organic light-emitting diodes because they allow for high quantum efficiencies by utilizing triplet states via reverse intersystem crossing. In small molecules, this is done by spatially separating the highest occupied molecular orbital from the lowest unoccupied molecular orbital, forming an intramolecular charge-transfer (iCT) state and leading to a small energy difference between lowest excited singlet and triplet states (ΔE ST ). However, in polymer emitters, this is harder to achieve, and typical strategies usually include adding known TADF units as sidechains onto a polymer backbone. In a previous work, we proposed an alternative way to achieve a TADF polymer by repeating a non-TADF unit, polymerizing it via electron-donating carbazole moieties. The extended conjugation on the backbone reduced the ΔE ST and allowed for an efficient TADF polymer. In this work, we present a more in-depth study of the shift from a non-TADF monomer to TADF oligomers. The monomer shows non-TADF emission, and we find the delayed emission to be of triplet−triplet annihilation origin. An iCT state is formed already in the dimer, leading to a much more efficient TADF emission. This is confirmed by an almost two-fold increase of photoluminescence quantum yield, a decrease in the delayed luminescence lifetime, and the respective spectral lineshapes of the molecules.

Research on alkylbenzene side-chain engineering of acceptors, which can affect the crystallinity of molecule and packing orientations of the blend films, has deeply promoted the development of organic solar cells...

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