guojun liu

A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.

Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.

Naphthalenediimide-based random copolymers (PNDI-TVTx) with different π-conjugated dithienylvinylene (TVT) versus π-nonconjugated dithienylethane (TET) unit ratios (x = 1000%) are investigated. The PNDI-TVTx-transistor electron/hole mobilities are affected differently, a result rationalized by molecular orbital topologies and energies, with hole mobility vanishing but electron mobility decreasing only by ≈2.5 times when going from x = 100% to 40%.

All-polymer solar cells with 7.57% power conversion efficiency are achieved via a new perylenediimide-based polymeric acceptor. Furthermore, the device processed in ambient air without encapsulation can still reach a high power conversion efficiency (PCE) of 7.49%, which is a significant economic advantage from an industrial processing perspective. These results represent the highest PCE achieved from perylenediimide-based polymers.

A small-molecular acceptor, tetraphenylpyrazine-perylenediimide tetramer (TPPz-PDI₄), which has a reduced extent of intramolecular twisting compared to two other small-molecular acceptors is designed. Benefiting from the lowest extent of intramolecular twisting, TPPz-PDI₄ exhibits the highest aggregation tendency and electron mobility, and therefore achieves a highest power conversion efficiency of 7.1%.

Donor–acceptor–acceptor′ small-molecule donors are synthesized to investigate regioisomeric effects on organic photovoltaic device performance. Cross-conjugation in 2-((7-(N-(2-ethylhexyl)-benzothieno[3,2-b]thieno[3,2-d]pyrrol-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)malononitrile leads to an increased open-circuit voltage compared with its isomer 2-((7-(N-(2-ethylhexyl)-benzothieno[3,2-b]thieno[2,3-d]pyrrol-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)methylene)malononitrile. A correlation is then established between molecular conjugation length and orbital energies, and hence open-circuit voltage.

“Molecule-framework” and “side-chain” engineering is powerful for the design of high-performance organic semiconductors. Based on 2DQTTs, the relationship between molecular structure, film microstructure, and charge-transport property in organic thin-film transistors (OTFTs) is studied. 2DQTT-o-B exhibits outstanding electron mobilities of 5.2 cm² V^–1 s^–1, which is a record for air-stable solution-processable n-channel small-molecule OTFTs to date.

A novel non-fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high-lying lowest unoccupied molecular orbital level of −3.95 eV, is designed and synthesized by introducing electron-donating alkoxy groups to the backbone of a conjugated small molecule. Impressive power conversion efficiencies of 8.4% and 10.7% are obtained for fabricated single and tandem polymer solar cells.

A nonfullerene polymer solar cell with a high efficiency of 9.26% is realized by using benzodithiophene–alt–fluorobenzotriazole copolymer J51 as a medium-bandgap polymer donor and the low-bandgap organic semiconductor ITIC with high extinction coefficients as the acceptor.

Efficient sky-blue organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) display a three orders of magnitude increase in lifetime, which is superior to those of controlled phosphorescent OLEDs used in this study. The combination of electro-oxidation and photo-oxidation of the TADF emitters in their triplet excited-states is suppressed through molecule design and device engineering.

Planar backbone, locked conformation, and low lowest unoccupied molecular orbital level provide polymer F₄BDOPV-2T with ultrahigh electron mobilities of up to 14.9 cm² V⁻¹ s⁻¹ and good air stability. It is found that the nonlinear transfer curves can be tuned to near-ideal ones by changing fabrication conditions, indicating that film morphology largely contributes to the nonlinear transfer curves in high-mobility conjugated polymers.

Extremely efficient sky-blue organic electroluminescence with external quantum efficiency of ≈37% is achieved in a conventional planar device structure, using a highly efficient thermally activated delayed fluorescence emitter based on the spiroacridine–triazine hybrid and simultaneously possessing nearly unitary (100%) photoluminescence quantum yield, excellent thermal stability, and strongly horizontally oriented emitting dipoles (with a horizontal dipole ratio of 83%).

Three small molecules as front cell donors for tandem cells are thoroughly evaluated and a high power conversion efficiency of 11.47% is achieved, which demonstrates that the oligomer-like small molecules offer a good choice for high-performance tandem solar cells.

A novel electron-deficient building unit, dithienylthienothiophenebisimide, and its polymers (PTBIs) are reported. Organic photovoltaic (OPV) cells based on PTBIs as p-type material exhibit 8.0% efficiencies with open-circuit voltages higher than 1 V. Interestingly, PTBIs also function as n-type material in OPVs depending on the molecular structure. These polymers also exhibit p-channel, n-channel, and ambipolar behaviors in field-effect transistors.

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. A bright, renal-excreted, and biocompatible near-infrared II fluorophore for in vivo imaging of TBI is designed. A transient hypoperfusion in the injured cerebral region, followed by fluorophore leakage, is observed. NIR-II fluorophores can provide noninvasive assessment of TBI.