ZnO nanowires for solar cells: a comprehensive review

As an abundant and non-toxic wide band gap semiconductor with a high electron mobility, ZnO in the form of nanowires (NWs) has emerged as an important electron transporting material in a vast number of nanostructured solar cells. ZnO NWs are grown by low-cost chemical deposition techniques and their integration into solar cells presents, in principle, significant advantages including efficient optical absorption through light trapping phenomena and enhanced charge carrier separation and collection. However, they also raise some significant issues related to the control of the interface properties and to the technological integration. The present review is intended to report a detailed analysis of the state-of-the-art of all types of nanostructured solar cells integrating ZnO NWs, including extremely thin absorber solar cells, quantum dot solar cells, dye-sensitized solar cells, organic and hybrid solar cells, as well as halide perovskite-based solar cells.

Photoelectrochemical water splitting strongly enhanced in fast-grown ZnO nanotree and nanocluster structures

We demonstrate selective growth of ZnO branched nanostructures: from nanorod clusters (with branches parallel to parent rods) to nanotrees (with branches perpendicular to parent rods). The growth of these structures was realized using a three-step approach: electrodeposition of nanorods (NRs), followed by the sputtering of ZnO seed layers, followed by the growth of branched arms using hydrothermal growth. The density, size and direction of the branches were tailored by tuning the deposition parameters. To our knowledge, this is the first report of control of branch direction. The photoelectrochemical (PEC) performance of the ZnO nanostructures follows the order: nanotrees (NTs) > nanorod clusters (NCs) > parent NRs. The NT structure with the best PEC performance also possesses the shortest fabrication period which had never been reported before. The photocurrent of the NT and NC photoelectrodes is 0.67 and 0.56 mA cm^-2 at 1 V vs. Ag/AgCl, respectively, an enhancement of 139% and 100% when compared to the ZnO NR structures. The key reason for the improved performance is shown to be the very large surface-to-volume ratios in the branched nanostructures, which gives rise to enhanced light absorption, improved charge transfer across the nanostructure/electrolyte interfaces to the electrolyte and efficient charge transport within the material.

Light-soaking effects on ZnO-nanorods/polymer hybrid photovoltaics

In ZnO-nanorods/polymer hybrid photovoltaics, molecular oxygen adsorbed on ZnO-nanorods is very harmful because it provides quenching and recombination pathways to excitons. By UV irradiation, photocurrent is increased as a result of its desorption.

Surface-initiated polymerization of A–A/B–B type conjugated monomers by palladium-catalyzed Stille polycondensation: towards low band gap polymer brushes

A surface-initiated Stille polycondensation from Pd catalyst-immobilized ZnO nanorods affords well-defined core–shell nanoparticles. For the first time, a low band gap polymer was anchored on ZnO nanorods to create hybrid materials with tunable photophysical properties.