Nanowires are being produced and integrated into various systems today, including solar cells, nano-sensors, nano-electrodes, transparent touch-screen coatings, and LED replacements. Thus far, several challenges have hindered the commercial advancement of nanowire-based technologies. Two major setbacks have been: (1) the lack of compatibility with existing platforms, mostly silicon technology and (2) low cell voltage, due to an in-parallel rather than in-series nanowire array integration, limiting the open-circuit voltage to less than 1 V whereas the voltage necessary to power certain devices can be several volts and up. Researchers from the Weizmann Institute of Science have demonstrated a unique method that can solve these problems. The new technology is silicon-compatible and allows in-series nanowire integration, resulting in high voltage cells on a reduced size chip, thus expanding the application opportunities for nanowire photovoltaic technologies, such as light harvesting and autonomous powering of IoT components.
PV cells and photodetectors for:
- Light harvesting/light sensing systems for IoT related systems
- BIPV (Building Integrated Photovoltaics) applications including smart windows
- Transparent coating for touch screens/LED replacements
- High-density data storage devices.
A silicon-based integrated technology for high voltage photovoltaic generation:
- Increased and easily scaled-up voltage on the same chip using an in-series nanowire integration ·
- Can be applied via existing production technologies (e.g. lithography in silicon wafers) and be integrated into existing systems, including CMOS and MEMS based products.
The research focused on two areas; (1) novel generic methods for nanowire growth via nanolithography and (2) production of in-series photovoltaic cells from core-shell nanowire arrays. Guided growth of planar nanowire arrays with custom-designed shapes on amorphous substrates was achieved by fabricating trenches via nanolithography in two novel configurations that were found to be useful for nanowire guided growth by artificial epitaxy. The precise dimensions of the trenches as well as the growth parameters can be optimized for each material to improve the yield and morphology. For the production of planar in series nanowire-based photovoltaic cells, CdS-Cu2S core-shell arrays on insulating substrate were produced by the combination of vapor-phase surface-guided horizontal growth and solution-proceeded cation exchange reaction. Consequently, the researchers were able to demonstrate an easy to scale-up, straightforward implementation method for fabrication of photovoltaic cells based on core-shell nanostructures. They additionally presented the facile monolithic integration of microscale cell photovoltaic modules with parallel or series configuration based on these core-shell arrays. An open-circuit voltage, up to 2.5 V was obtained from a tandem module, with 4 unit cells connected in series with a potential for an even larger number of in-series unit integration. The presented modules are promising autonomous power sources for next-generation integrated nano-systems and autonomous wireless-electronics.
Guided horizontal nanowires growth. (A) Schematic view of guided growth (right) versus conventional growth (left). (B) Three modes of guided growth (schematic cross-sectional views). (C) Experimental realization of (B) for GaN nanowires. (D) Ultralong (>1 mm), unidirectional GaN nanowires.