Quasi-solid-state self-assembly of 1D-branched ZnSe/ZnS quantum rods into parallel monorail-like continuous films for solar devices

Translating the extraordinary optoelectric properties of colloidal quantum rods (QRs) into functional devices requires multiscale structural control to preserve the nanoscale attributes as well as to introduce micro- and macroscale interactions between the building blocks. Self-assembly of anisotropic QRs into ordered nanostructures can tailor the photoelectric properties of the QRs, such as in light absorption, and charge separation and transfer. However, it remains a challenge to assemble anisotropic nanomaterial into centimeter-sized, multilayered continuous films that retain nanoscale properties in the fabricated macroscopic devices. We have developed a quasi-solid-state self-assembly of randomly oriented nanostructures for overcoming this challenge, demonstrated by the re-assembly of randomly packed ZnSe/ZnS QRs into aligned and ordered parallel monorails (PMs). These ZnSe/ZnS PMs show significant enhancement in photo-excited charge transport, boosting photocatalytic oxygen evolution rates and the enhancement of photoelectrochemical activities, with a photocurrent density of 18 μA/cm², 5 times higher than the parent random packing of ZnSe/ZnS QRs. The ZnSe/ZnS PMs enrich the p-n heterojunctions, which can modulate charge carrier separation and transport at the interfaces. The new method has applicability for re-assembling randomly packed films of anisotropic nanoparticles into ordered nanostructures. Importantly, the extraordinary photoelectro-energy conversion behavior of the Type-I core/shell quantum materials illuminates the pathways for novel designed materials by tailoring the hierarchical structures at all scales.