Hybridization of an n-type semiconducting polymer with PbS quantum dots and their photovoltaic investigation

Abstract

Herein, we synthesize a new organic-inorganic hybrid material by direct coordination of a chain-end-functionalized naphthalene diimide (NDI)-based n-type semiconducting polymer with thiol group(s), PNDI-SH, to lead sulfide quantum dots (PbS-QDs). PNDI-SH was successfully synthesized by the thiolation of a chain-end-functionalized NDI-based polymer with bromobutyl group(s), PNDI-Br, under optimized conditions for the end-capping reaction. The synthesized hybrid n-type material, PNDI-SH:PbS-QD (70:30, w-w), was found to show good dispersibility in organic solvents and excellent atmospheric stability even after storage for 8 months. This is due to the uniform coating of polymer chains of PNDI-SH on the PbS-QD surfaces. The ultraviolet-visible-near-infrared (UV-Vis-NIR) absorption spectrum for PNDI-SH:PbS-QD (70:30, w-w) shows distinct spectral shifts in the NIR region corresponding to PbS-QDs after hybridization with PNDI-SH. In addition, the formation of PbS-QD nanoclusters is confirmed by transmission electron microscopy (TEM) for a PNDI-SH:PbS-QD (70:30, w-w) thin film, while only PbS-QD nanoparticles are observed in the PNDI-Br:PbS-QD (70:30, w-w) thin film without nanoclusters. We then examined the photovoltaic performance of PNDI-SH:PbS-QD (70:30, w-w) as the polymer acceptor, which, despite showing the capability of being a polymer acceptor, showed an overall photovoltaic performance that is inferior to that of the pristine polymer acceptor N2200. This can be attributed to the downshifted energy levels of PNDI-SH:PbS-QD (70:30, w-w) and its unfavorable morphology. Hybridization with PbS-QDs induces phase separation due to self-aggregation of PbS-QDs, which is unfavorable for efficient exciton dissociation and charge transport. ? 2021, The Author(s), under exclusive licence to The Society of Polymer Science, Japan.