The worldwide increasing number of electronic devices working at the same time supposes a huge demand for on-site power that cannot be supplied by conventional batteries. So, the development of environmental energy harvesters is critical to prompt the self-powered actuation of small, portable-wearable, and wireless electronic devices. In this context, the nanogenerators arise as efficient nanoelectrodes that avoid energy losses and enhance multifunctionality.

The nanoscale design of conductive and transparent materials for these nanoelectrodes is a crucial step for different applications that include optoelectronics and photovoltaics devices and energy harvesters and it is essential in the management of light harvesting under low-intensity conditions. One of the main interests in this direction is the use of new transparent conducting nanoelectrodes consisting of a wide range of materials with different compositions and texturing such as metal nanowires networks, carbon nanotubes, graphene, transparent conducting oxides (TCOs) nanostructures, etc.

In this work, we have synthesized 1-dimensional (1D) and hierarchical Indium Tin Oxide (ITO) nanoelectrodes by a soft-template multistep method that combines vacuum and plasma techniques in a “one-reactor/chamber” configuration.^[1] Here, we combined magnetron sputtering and thermal evaporation, two industrially spread deposition techniques. In particular, we have synthesized high-quality ITO nanotubes with resistivities on single-nanotube comparable with single-crystal nanowires reported by other authors. These nanoelectrodes present desirable optical properties in the visible spectra for enhancing light trapping in energy harvesting applications.

The implementation of these nanostructures in Dye-Sensitized Solar Cells (DSSCs) has been carried out following a standard architecture of a photovoltaic device. The photoanode was prepared in two steps to cover the ITO nanostructures with anatase-TiO₂: 1) a conformal shell by Plasma Enhanced Chemical Vapor Deposition for then 2) embedding in a mesoporous matrix by screen-printing. The multi-layered system has been sensitized with the YKP-88 dye. ^[2] To complete the DSSC, we have used a platinum counter electrode on FTO glass (fluorine tin oxide) and two electrolytes based on the iodide/tri-iodide redox pair. The difference between the electrolytes lies in the viscosity: 1) liquid-based and 2) ionic liquid-based, the former having lower viscosity.

The photovoltaic performance of these devices has been measured under a solar simulator (100 mW/cm²) as well as under indoor sources such as white LED (6500 K) over a wide range of intensities (1.77 mW/cm² to 0.014 mW/cm²). The main results of this study indicate an outstanding increment of the DSSC efficiency incorporating 1D nanoelectrodes for low light intensity conditions. This is a behavior that does not happen with the reference samples (without 1D nanoelectrodes). Such is the increase in efficiency of the 1D nanostructured DSSCs, that they show the highest performance values at lower intensities, above the reference samples.