Singlet Exciton Delocalization in Gold Nanoparticle-Tethered Poly(3-hexylthiophene) Nanofibers with Enhanced Intrachain Ordering

Polaron Pair-Mediated Radiative Recombination of Singlet Excitons in a Conjugated Polymer Aggregate by Plasmonic and Semiconductor Nanocrystals

We investigated the excited-state dynamics of a conjugated polymer (CP:P3HT)-based ternary hybrid system containing P3HT-coated gold nanoparticles and quantum dots. Transient absorption spectroscopy results revealed that polaron pairs (PPs) originating from nonrelaxed singlet (S1) excitons of the CP aggregate in the ternary system have shorter electron-hole separation distances than those of PPs in the neat CP aggregate because of the photophysical effects of plasmonic and semiconductor nanocrystals. In particular, the shorter electron-hole distances of PPs led to more back-recombination to S1 excitons than dissociation into positive polarons in the ternary system, resulting in increased S1 radiative recombination compared with that in the neat CP system. Thus, the photoluminescence intensity of the CP aggregate in the ternary system increased. Our findings provide new insights into the excited-state dynamics of CPs and pave the way for the development of next-generation high-efficiency optoelectronic devices.

Flexible Polymer-Assisted Mesoscale Self-Assembly of Colloidal CsPbBr3 Perovskite Nanocrystals into Higher Order Superstructures with Strong Inter-Nanocrystal Electronic Coupling

Surface-passivating ligands, although ubiquitous to colloidal nanocrystal (NC) syntheses, play a role in assembling NCs into higher order structures and hierarchical superstructures, which has not been demonstrated yet for colloidal CsPbX₃ (X = Cl, Br, and I) NCs. In this work, we report that functional poly(ethylene glycols) (PEG₆-Y, Y = -COOH and -NH₂) represent unique surface-passivating ligands enabling the synthesis of near-uniform CsPbBr₃ NCs with diameters of 3.0 nm. The synthesized NCs are assembled into individual pearl necklaces, bundled pearl necklaces, lamellar, and nanorice superstructures, in situ. It is believed a variety of forces, including van der Waals attractions between hydrophilic PEG tails in a nonpolar solvent and dipole-dipole attraction between NCs, drive mesoscale assembly to form superstructures. Furthermore, postsynthetic ligand treatment strengthens the argument for polymer-assisted mesoscale assembly as pearl necklace assemblies can be successfully converted into either lamellar or nanorice structures. We observe an ∼240 meV bathochromic shift in the lowest energy absorption peak of CsPbBr₃ NCs when they are present in the lamellar and nanorice assemblies, representing strong inter-NC electronic coupling. Moreover, pearl necklace structures are spontaneously assembled into micrometer length scale twisted ribbon hierarchical superstructures during storage of colloidal CsPbBr₃ NCs. The results show that the self-assembled superstructures of CsPbBr₃ NCs are now feasible to prepare via template-free synthesis, as self-assembled structures emerge in the bulk solvent, a process that mimics biological systems except for the use of nonbiological surface ligands (PEG₆-Y). Taken together, emergent optoelectronic properties and higher order superstructures of CsPbBr₃ NCs should aid their potential use in solid-state devices and simplify scalable manufacturing.