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- Zhang, Jiangbin, et al.
(författare)
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Efficient non-fullerene organic solar cells employing sequentially deposited donor-acceptor layers
- 2018
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 6:37, s. 18225-18233
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Tidskriftsartikel (refereegranskat)abstract
- Non-fullerene acceptors (NFAs) have recently outperformed their fullerene counterparts in binary bulk-heterojunction (BHJ) organic solar cells (OSCs). Further development of NFA OSCs may benefit other novel OSC device structures that alter or extend the standard BHJ concept. Here, we report such a new processing route that forms a BHJ-like morphology between sequentially processed polymer donor and NFA with high power conversion efficiencies in excess of 10%. Both devices show similar charge generation and recombination behaviours, supporting formation of similar BHJ active layers. We correlate the approximate to 30 meV smaller open-circuit voltage in sq-BHJ devices to more substantial non-radiative recombination by voltage loss analysis. We also determine the exciton diffusion length of benchmark polymer PBDB-T to be 10 +/- 3 nm. Our results demonstrate high-efficiency OSC devices using sequential deposition method and provide new opportunities to further improve performance of state-of-the-art OSCs.
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- Gillett, Alexander J., et al.
(författare)
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Spontaneous exciton dissociation enables spin state interconversion in delayed fluorescence organic semiconductors
- 2021
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Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Engineering a low singlet-triplet energy gap (Delta E-ST) is necessary for efficient reverse intersystem crossing (rISC) in delayed fluorescence (DF) organic semiconductors but results in a small radiative rate that limits performance in LEDs. Here, we study a model DF material, BF2, that exhibits a strong optical absorption (absorption coefficient = 3.8 x 10(5) cm(-1)) and a relatively large Delta E-ST of 0.2 eV. In isolated BF2 molecules, intramolecular rISC is slow (delayed lifetime = 260 mu s), but in aggregated films, BF2 generates intermolecular charge transfer (inter-CT) states on picosecond timescales. In contrast to the microsecond intramolecular rISC that is promoted by spin-orbit interactions in most isolated DF molecules, photoluminescence-detected magnetic resonance shows that these inter-CT states undergo rISC mediated by hyperfine interactions on a similar to 24 ns timescale and have an average electron-hole separation of >= 1.5 nm. Transfer back to the emissive singlet exciton then enables efficient DF and LED operation. Thus, access to these inter-CT states, which is possible even at low BF2 doping concentrations of 4 wt%, resolves the conflicting requirements of fast radiative emission and low Delta E-ST in organic DF emitters.
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