SILICON_LIGHT

Improved material quality and light trapping in thin film silicon solar cells

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 Obiettivo del progetto (Objective)

'In this project we will increase the efficiency of thin-film silicon solar cells on flexible substrates by solving the issues linked to material quality, interface properties and light management, thus enabling lower production costs per Watt-peak. The general technological objectives of the project are the development of better materials and enhanced interfaces for thin film silicon solar cells, and to transfer the developed processes to an industrial production line. The most important project goals are: 1) Reduction of optical reflection and parasitic absorption losses: Design and industrial implementation of textured back contacts in flexible thin film silicon solar cells. 2) Reduction of recombination losses: Development and implementation of improved silicon absorber material. 3) Reduction of electric losses: Graded TCO layers which minimize the work function barrier between the p-layer and the TCO layer without loss of conductivity and transmission of the TCO. In addition, the top layer of the TCO stack should provide a good protection against moisture ingression. In order to achieve these objectives more in-depth knowledge is needed for several relevant key areas for thin film silicon solar cells. The main scientific objectives are: 1) Identification of the ideal texture for the back contact. This structure should maximize the light trapping in thin film silicon solar cells without deterioration of open-circuit voltage and fill factor. 2) Paradigm shift for the growth of microcrystalline silicon. In this project we want to show that it is possible to use microcrystalline silicon with high crystalline fractions leading to better current collection without voltage losses, and without crack formation when grown on nano-textured substrates. 3) Deeper understanding of moisture degradation mechanisms of common TCO’s like ITO and AZO.'

Descrizione progetto (Article)

Solar cell technology that harnesses sunlight to produce electricity is already being implemented commercially in solar panels around the world. However, deep and broad market penetration requires overcoming the current bottlenecks with regard to efficiency and costs.

Scientists initiated the EU-funded project 'Improved material quality and light trapping in thin film silicon solar cells' (http://www.silicon-light.eu/ (SILICON_LIGHT)) to increase efficiency and thus decrease energy production costs. Partners developed high-quality, very thin-film silicon layers on inexpensive plastic foil.

Technical goals included developing appropriate textured back contacts to maximise light-trapping in thin films and improved microcrystalline silicon absorber materials for better current collection. In addition, novel transparent conductive oxide (TCO) layers should reduce electric losses and moisture degradation.

Scientists fabricated foils of 30-cm length with textured back contacts. To enhance efficiency, they applied microcrystalline silicon with high crystalline fractions using deposition processes that prevent or mitigate crack formation. High-resolution tunnelling electron microscopy was used to investigate layers.

New TCO materials were developed that combined the advantages of indium tin oxide and zinc oxide and were successfully applied in a pilot-scale production plant. Among these alternative materials, one with improved performance-to-cost ratio was identified. In addition, solar cells made from amorphous silicon with rear side light-scattering texture were fabricated in pilot-scale production.

Materials and components from SILICON_LIGHT innovations are already planned for use by project partners in a variety of components and devices. Ultimately, availability of high-efficiency solar cells with lower prices could positively impact renewable energy usage benefitting manufacturers, end users and the environment.