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, two major drawbacks in the advancement of nanowire-based technologies have been: (1) the lack of compatibility with existing platforms, mostly silicon technology, and (2) limited cell voltage. 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 application opportunities for nanowire photovoltaic technologies, such as light-harvesting and autonomous powering of IoT components. Modules produced in this method are, therefore a promising autonomous power sources for next-generation integrated nano-systems and autonomous wireless electronics.
Most nanowire-based photovoltaic cells and photodetectors are based on vertical arrays, which can only be integrated in parallel (not in series), limiting their open-circuit voltage to less than 1 V whereas the voltage necessary to power certain devices can be several volts and more. This new nanowire technology enables the achievement of high voltage photovoltaic cells necessary to power a variety of microsystems; moreover, such cells can be integrated with other systems on the same chip. This technology can allow photovoltaic integration into autonomous microsystems, higher solar energy utilization, and expansion of photovoltaic cell applications. With the growing need for systems allowing renewable energy harvesting and ever-increasing performance demands – such as speed, efficiency, size, and lower cost, an efficient nanowire-based photovoltaic technology can be of high value and applied into a variety of market sectors.
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 novel configurations that were found to be effective for nanowire guided growth by artificial epitaxy. 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. Consequently, the researchers were able to demonstrate an easy to scale-up, straightforward implementation method for photovoltaic cells fabrication based on core-shell nanostructures. 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.
- A silicon-based integrated technology for high voltage photovoltaic generation:
- Increased and easily scalable voltage on the same chip using an in-series nanowire integration
- Can be applied using existing production technologies (e.g. lithography in silicon wafers) and integrated into existing systems, including CMOS and MEMS based products.
- 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.
The Weizmann Institute researchers have successfully demonstrated integration of up to four planar nanowire solar cell arrays in series, in which the open-circuit voltage was increased from 0.6 V to 2.4 V (via connecting up to four cells in series). This result has been achieved using guided growth of planar nanowires of different materials, along lithographic open trenches on amorphous silicon oxide-coated silicon wafers (compatible with CMOS and MEMS technologies).
A European Research Council Proof-of-Concept (ERC-PoC) grant was aimed at developing applications based on this pending patent technology. Ongoing work with promising results focuses on: (1) micro-PV cells and (2) IR detectors.
The increasing need for alternative energy sources, propelled by extensive governmental initiatives, has powered the drastic growth of the solar energy market in recent years. According to recent reports, the global solar energy market will reach about $422 billion by 2022, growing at a CAGR of 24.2%. Therefore, solutions that potentially increase energy harvesting efficiency will have a huge advantage in this field.
Market need for Weizmann’s novel nanowire-based photovoltaic technology is most likely to concentrate in two areas:
- IoT: The increasing need to power on-chip autonomous microsystems, with demands that will surpass the limitations of conventional limited lifetime batteries, is anticipated to drastically grow and impact an increasing variety of fields, including communication, surveillance, and IoT. The IoT market alone is anticipating reaching $457 billion by 2020, growing at a CAGR 28.5%, as was recently reported.
- Building integrated photovoltaics (BIPV): The incorporation of solar energy harvesting systems to areas with limited sunlight further expands the photovoltaic market demands. The BIPV market is expected to reach $5.7 billion in 2023 and $11.6 billion in 2027, according to recent reports.