Molecular-Level Switching of Polymer/Nanocrystal Non-Covalent Interactions and Application in Hybrid Solar Cells

Hybrid composites obtained upon blending conjugated polymers and colloidal semiconductor nanocrystals are regarded as attractive photoactive materials for optoelectronic applications. Here it is demonstrated that tailoring nanocrystal surface chemistry permits to control non-covalent and electronic interactions between organic and inorganic components. The pending moieties of organic ligands at the nanocrystal surface are shown to not merely confer colloidal stability while hindering charge separation and transport, but drastically impact morphology of hybrid composites during formation from blend solutions. The relevance of this approach to photovoltaic applications is demonstrated for composites based on poly(3-hexylthiophene) and lead sulfide nanocrystals, considered as inadequate until this report, which enable the fabrication of hybrid solar cells displaying a power conversion efficiency that reaches 3%. By investigating (quasi) steady-state and time-resolved photo-induced processes in the nanocomposites and their constituents, it is ascertained that electron transfer occurs at the hybrid interface yielding long-lived separated charge carriers, whereas interfacial hole transfer appears hindered. Here a reliable alternative aiming to gain control over macroscopic optoelectronic properties of polymer/nanocrystal composites by mediating their non-covalent interactions via ligands' pending moieties is provided, thus opening new possibilities towards efficient solution-processed hybrid solar cells.