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Accelerating Commercialization of Nanowire Solar Cell Technologies

Periodic Reporting for period 3 - NanoSol (Accelerating Commercialization of Nanowire Solar Cell Technologies)

Reporting period: 2018-02-01 to 2019-04-30

Fighting climate change, reducing pollution, and phasing out fossil fuels means the world needs to develop revolutionary clean and renewable energy technologies. Sol Voltaics’ NanoSol project is addressing this challenge and its technology will help produce previously unreachable levels of low-cost solar power through the development of high efficiency nanowires.

As efficiency is the most important factor in reducing the cost of solar electricity – since all area related costs are reduced by the overall power output of a PV module – the promise of SolFilm™ is significant.

Manufactured using Sol Voltaics’ revolutionary Aerotaxy® process, SolFilm offers a solution that will boost silicon solar modules to break through the efficiency barrier for a single layer semiconductor. Module efficiencies of over 25% will be possible using SolFilm in conjunction with standard silicon cell technologies and maxima close to or even beyond 30% efficiency are feasible. The cost of these modules will only be 5-10% higher in cost per Wp, resulting in a reduction in the installation cost per Wp for rooftop systems.

SolFilm has been designed for straightforward module integration and the low-cost approach to manufacturing high-efficiency multijunction solar panels helps reduce the levelized cost of energy (LCOE), for module manufacturers and end-users.

SolFilm also positively transforms the aesthetics of solar modules, providing a uniform black surface because of its thin-film nature, all different kind of sizes and shapes are possible without losing efficiency. As solar energy adoption continues to increase, the appearance of solar modules, particularly within urban areas, is becoming more important.

The overall objectives for the NanoSol project are to improve the Aerotaxy production methodologies in order to deliver an improved SolFilm product at reduced cost and also to validate the performance improvements by integrating SolFilm with devices from selected PV module manufacturers to form tandem solar modules with the aim to verify increased efficiency from 18% to 27% on silicon cells. Another overall objective is to prepare the technology for large-scale industrialization and commercialization.
In WP1 further progress was made in both the stability and uptime of the so called G4 reactor. Having the tool in operation 5 days a week, sufficient wires could be fabricated to supply all the work performed in WP2.

The new G5 reactor has demonstrated to be able to make nanowires with both passivation and pn-junction. These full solar nanowires are the first ever grown using Aerotaxy.
Based on the further learnings from both the G4 and the G5 tool, a start has been made with the design of the next generation of Aerotaxy furnace. This furnace will address modularity, and especially system control.

In WP2 the first solar cells (filmcells) were obtained based on the nanowire membranes that were fabricated according to the Solfilm production process. These solar cells were fabricated using MOCVD wires and resulted in efficiencies close to the 5% target efficiencies.
The size of the nanowire membranes has been increased from an 8-inch disc (approx. 200 mm diameter) to a rectangle of 156 x 950 mm. This size has been chosen as this is the width of a 60-cell silicon module and the height of a single cell. Increasing the size to these dimensions in a single step gives high confidence that the next step to full module size will not lead to fundamental issues. The quality of this membrane has been checked at multiple locations and is in all locations according to the specs for the 5% efficiency target.

In WP3 the main activity is to build a new cleanroom that allows the fabrication of solar cells or modules with a size of 156 mm x 156 mm. This is the size that is indicated by the commercial partners, future customers, and participants in the sample program as being the minimum size required to ship Solfilm-based products to the final customers for sampling. This cleanroom opened in March 2018 and is producing filmcell samples.

In WP4 the goal is to fabricate tandem solar cells and module demonstrators together with partners. For this, a sample program has been started in which membranes, solar cells, and modules will be delivered to prove the progress made and allow the potential customer to start initial integration experiments.

In WP5 focus lies on the dissemination of project results and the development of an ecosystem of partners in the value chain. Sol Voltaics has continued building momentum for their new technology using press releases, company visits and relaunching the company website. The attention from the market has resulted in additional funding. A funding round of $21.3M was closed in 2017, which, in the recent years, is a record for a PV startup. The ecosystem surrounding Sol Voltaics continues to grow.

In WP6 the activities required to form relationships and partnerships in order to successfully
bring SolFilm to market are described. A major step in the last year has been to increase ties to potential producers of the Solfilm modules. Interest from large companies already in possession of suitable production equipment has resulted in closer collaboration.
Eight patents have been granted in Japan, China, USA, South Korea and Europe.
In the project proposal the below key areas where identified as innovation beyond state-of-the-art:
• Aerotaxy allows growth of nanowires in the gas phase without a substrate
• The resulting nanowires are then processed via encapsulation into a nanowire ink
• This ink is itself printed into thin nanowire films using a number of advanced processes to transform encapsulated nanowires into oriented 2D structures
• Using nanowires allows the production of highly-efficient GaAs Thin Films at a fraction (10%) of current active materials requirements

Progress towards and beyond state-of-the-art:
In the second part of the project progress has been made on all above areas;
In terms of Aerotaxy technology, Solvoltaics has demonstrated it is possible to grow nanowires with complicated structures, containing both an pn-junction and a passivating shell directly from the gas phase. These nanowires have been proven to show all functionality needed to produce solar cells.

Secondly, the encapsulation of a passivating layer in the ink process has been developed into a very high yield process and works both on MOCVD and Aerotaxy wires. This key concept also allows spacing control of the wires in the film, which enables tuning of the membrane absorption properties.

Sol Voltaics has proven that it is possible to fabricate nanowire membranes with a surface of over 1400 cm2 with a high degree of uniformity. This size is large enough to produce six 156 mm x 156 mm membranes at a time. The rapid progress in increasing size shows a high confidence in being able to produce membranes of module size or even larger.

The low-cost, easy to integrate solution that NanoSol brings forward will increase the power output of conventional silicon modules without increasing installation cost and thus reducing the cost of electricity generated by solar power.
Oriented nanowires in a membrane