(512b) Metal and Semiconductor Nanowire Network Thin Films with Hierarchical Pore Structures and Its Photovoltaic Applications

Nanoscale building blocks, such as quantum dots, nanoparticles, nanorods, nanowires, nanobelts, nanotubes, and nanomesh, have attracted tremendous attention due to their peculiar and fascinating properties. It is necessary to assemble low dimensional nanoscale building blocks into nanostructured systems for the potential applications in energy storage, separation, catalysis, computation, sensing, etc. In this work, we report synthesis, characterization, photovoltaic and sensing applications of macroscopic metal or semiconductor nanowire networks with hierarchical porous structure. Metal and semiconductor nanowire network (e.g., Pt, CdSe) thin films with hierarchical pore structure were electrodeposited using mesoporous silica (primary porogens) containing colloidal silica particles (secondary porogens) as templates. The pore size of the nanowire thin films was independently controlled by the wall thickness of the surfactant-templated mesopores and the sizes of the incorporated silica particles. The mesostructure of the nanowire thin films (e.g., hexagonal and cubic mesostructures) was controlled by judicious choice of surfactant. Furthermore, the shape of the secondary pores (e.g., spherical and rod shapes) can be controlled using secondary porogens with various shapes. Such hierarchical nanowire thin films provide novel platforms for photovoltaic, sensor and other device applications. In order to demonstrate the advantage of such hierarchical porous networks, we fabricated photovoltaic devices by infiltrating the hole-conducting poly(3-hexylthiophene) into the electron-conducting CdSe nanowire thin films with and without the secondary pore channels. The heterojunction solar cells consisting of a CdSe nanowire network with secondary pore structure and poly(3-hexylthiophene) showed improved performance with a short circuit current of 2.4 mA/cm2 under AM 1.5 solar illumination, confirming the advantages of such hierarchical pore structure for actual device applications. In conclusion, this work provides an easy and efficient way to synthesize macroscopic hierarchical nanowire networks with well-controlled diameter and mesoscale arrangement, which will be of great interest for sensor, photovoltaic, and other applications.