PHOTONVOLTAICS

Nanophotonics for ultra-thin crystalline silicon photovoltaics

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 Obiettivo del progetto (Objective)

'The ambition of PhotoNvoltaics is to enable the development of a new and disruptive solar cell generation resulting from the marriage of crystalline-silicon photovoltaics (PV) with advanced light-trapping schemes from the field of nanophotonics. These two technologies will be allied through a third one, nanoimprint, an emerging lithography technique from the field of microelectronics. The outcome of this alliance will be a nano-textured thin-film crystalline silicon (c-Si) cell featuring a drastic reduction in silicon consumption and a greater cell and module process simplicity. It will thus ally the sustainability and efficiency of crystalline silicon PV with the simplicity and low cost of the current thin-film solar cells. The challenge behind PhotoNvoltaics lies behind the successful identification and integration of these nano-textures into thin c-Si-based cells, which aim is a record boost of the light-collection efficiency of these cells, without harming their charge-collection efficiency.

The goals of this project are scientific and technological. The scientific goal is two-fold: (1) to demonstrate that the so-called Yablonovitch limit of light trapping can be overcome, with specific nanoscale surface structures, periodic, random or pseudo-periodic, and (2) to answer the old question whether random or periodic patterns are best. The technological goal is also two-fold: (1) to fabricate thin c-Si solar cells with the highest current enhancement ever reached and (2) to demonstrate the up-scalability of this concept by fabricating patterns over industrially relevant areas. To reach these goals, PhotoNvoltaics will gather seven partners, expert in all the required fields to model and identify the optimal structures, fabricate them with a large span of techniques, integrate them into solar cells and, finally, assess the conditions of transferability of these novel concepts, that bring nanophotonics into PV, further towards industry.'

Introduzione (Teaser)

Solar cell technology is poised for a major breakthrough, promising sustainable electricity for the next few billion years. The breakthrough may come in the form of advanced light-trapping beyond conventionally accepted limits.

Descrizione progetto (Article)

Solar cells based on expensive single-crystal silicon (Si) wafers account for the majority of devices sold today. Thin-film Si solar cells significantly decreased costs but efficiencies were similar or lower on average. The new technologies in the pipeline are targeted at significantly higher efficiencies accompanied by lower costs to encourage widespread market uptake.

EU-funded scientists working on the project 'Nanophotonics for ultra-thin crystalline silicon photovoltaics' (http://www.photonvoltaics.org/ (PHOTONVOLTAICS)) aim at enabling such a new cell technology. Nano-texturing is expected to increase optical properties above conventionally accepted limits. Different lithography technologies, Nanoimprint, Hole-mask Colloidal, and Laser Interference t lithographies are assessed to integrate the special nanopatterns with crystalline silicon (c-Si) photovoltaics. Significantly less Si will be required, reducing costs, while the lithography techniques have been chosen for their low cost potential.

As a high-risk Future Emerging Technologies project, PHOTONVOLTAICS has set ambitious goals. Scientist set out to prove that nano-scale patterning surpasses standard random texturing, enabling light absorption to surpass generally accepted limits. Simultaneously, they are aiming for the highest short-circuit current enhancement ever with c-Si technology at a thickness less than 40 micrometres. This requires going beyond a mere improvement of light absorption by c-Si and to electrically convert this light into an effective current into the cell, without damaging its electrical properties.

Now at its midterm, scientists have reached their goals and expectations for this time period. They have all the required tools at hand, together with a roadmap for in-lab integration of nanopatterns into thin-film c-Si solar cells. Optical modelling has pointed to the optimal periodic front-surface patterns for solar stacks varying from 1-40 micrometres in thickness.

Assessment of optical and electrical properties of a variety of nanopatterns produced with three different lithography techniques led to identification of the most promising conditions for cell integration. This is the goal for the second half of the project.

PHOTONVOLTAICS plans to be the spark to the powder keg of photovoltaic technology, propelling renewable energy powered by the Sun into the market boom the industry has been working toward. That would have impressive effects on the decrease of the atmospheric carbon dioxide and climate change. It would also put the EU in the driver's seat of innovative technologies both for energy and for low-cost patterned surfaces in general.