Covalent Networking of a Conjugated-Polymer Photocatalyst to Promote Exciton Diffusion in the Aqueous Phase for Efficient Hydrogen Production

A conjugated polymer particle in an aqueous phase is covalently networked in 3D by crosslinking with azide groups, leading to significantly enhanced activity—a high photocatalytic H2 evolution rate (11 024 µmol g−1 h−1 (λ > 420 nm)) and a high apparent quantum yield (up to 0.8%). The reaction between the photoactive azide and the alkyl chains of the conjugated polymer provides more intact intermolecular polymeric interactions in the colloidal state, thus preventing physical swelling and inhibiting the recombination of photoproduced carriers. The covalent network efficiently promotes exciton diffusion, which greatly facilitates charge separation and transfer. The azide photo-crosslinking also leads to more compact and better-packed nanoparticles in the aqueous phase and efficient transfer of excitons to the outer surface of the nanoparticles, where photocatalytic reactions occur. These results show that photo-crosslinking can suppress the adverse effects of alkyl chains which inhibit photocatalytic performance. Therefore, covalent crosslinking is a promising strategy for the development of solar and hydrogen energy. © 2022 Wiley-VCH GmbH1

Stoichiometric Engineering of Cs2AgBiBr6 for Photomultiplication- Type Photodetectors

Photomultiplication (PM)-type photodetectors with a high external quantum efficiency (EQE) can be realized through adequately engineered trap states and trap-assisted charge injection. By strategically introducing slightly rich Bi and highly rich Br stoichiometric conditions, efficient trap states are realized for holes in lead-free Cs1.98AgBi1.15Br7.9 double perovskite (DP). With the diode structure of ITO/SnO2/Cs1.98AgBi1.15Br7.9/poly(3-hexylthiophene) (P3HT)/MoOx/Ag, where SnO2 and P3HT layers are used as the hole-and electron-blocking layers, respectively, successful realization of the selective hole trap and the resulting band bending/electron injection at the anode interface is demonstrated. As a result, a high EQE of similar to 16,000%, responsivity of similar to 50 A W-1, and specific detectivity of over 1012 Jones at -3 V are demonstrated. The origin of the suggested PM mechanism is discussed using photophysical and optoelectronic measurements and theoretical studies. This work ensures the successful demonstration of PM-type photodetectors using lead-free Cs2AgBiBr6 DP through strategic trap engineering

Exciton???Scissoring Perfluoroarenes Trigger Photomultiplication in Full Color Organic Image Sensors

We report an unprecedented but useful functionality of perfluoroarenes to enable exciton scissoring in photomultiplication-type organic photodiodes (PM-OPDs). Perfluoroarenes that are covalently connected to polymer donors via photochemical reaction enable us to demonstrate high external quantum efficiency and B-/G-/R-selective PM-OPDs without the use of conventional acceptor molecules. We investigated the operation mechanism of the suggested perfluoroarene-driven PM-OPDs, ???How can covalently bonded polymer donor:perfluoroarene PM-OPDs perform as effectively as polymer donor:fullerene blend-based PM-OPDs????. By employing a series of arenes and conducting steady-state/time-resolved photoluminescence and transient absorption spectroscopy analyses, we find that interfacial band bending between the perfluoroaryl group and polymer donor is responsible for exciton scissoring and subsequent electron trapping, which induces photomultiplication. Owing to the acceptor-free and covalently interconnected photoactive layer in the suggested PM-OPDs, superior operational and thermal stabilities were observed. Finally, we demonstrated finely patterned B-/G-/R-selective PM-OPD arrays that enable the construction of highly sensitive passive matrix-type organic image sensors