Work package 1: Management

This work package deals with the overall technical and scientific management of the project. The main objectives in this WP are:

  • Overall technical and scientific project management
  • Financial management
  • Reporting to the EU
  • Public relation, dissemination and ensuring exploitation of results

Work package 2: Light trapping

Light trapping is of uppermost importance for thin film silicon solar cells in order to obtain high cell efficiencies. So far, only ad-hoc solutions have been applied in n-i-p type solar cells. In this work package we will pursuit a fundamentally new scientific and technologic approach through the following steps:

  1. Theoretical determination of ideal nano-textures, based on periodic structures, for efficient scattering at back contact using computer modeling.
  2. Fabrication of ideal textures through an embossing process,
  3. implementation of textured back contacts in small n-i-p cells (a-Si, mc-Si and a-Si/mc-Si tandems) on foil.

The novelty of this approach is that full control of the texturization is obtained and that theoretically ideal structures for light trapping can be implemented.

Work package 3: Silicon layers

Current state of the art thin film silicon solar cells have efficiencies which are still far below the theoretical limits. A crucial means to increase these efficiencies is to implement improved light scattering schemes. These schemes will be developed in WP2 but straightforward implementation can have detrimental effects on efficiency, because texturization of the substrate can lead to crack and void formation in the silicon layers. One main objective of this work package is to develop silicon deposition processes which prevent or mitigate crack formation in microcrystalline silicon, when grown on texturized substrates. A crucial interface in this respect and which will be deeply investigated an optimized in this WP is the n-i silicon interface. Further the potential harm of p-layer growth on the i-p silicon interface will be investigated in order to prevent this damage. Another efficiency limiting factor which will be tackled in this work package is the relatively low Vocs which are currently obtained for microcrystalline silicon solar cells. The common approach to obtain reasonable Voc is to use microcrystalline silicon with a rather high amorphous fraction, but this has its price through lower currents and stability. In this WP we will investigate ways to apply microcrystalline silicon with higher crystalline fractions, without detrimental effects for the Voc of the cells.

Work package 4: TCO layers

Transparent Conductive Oxide (TCO) layer play an essential role in the functionality of thin film solar cells in general, and thin film silicon solar cells in particular. Commonly used TCOs are presently ITO and doped ZnO (see photo), but both materials have certain disavantages with respect to cost and performance. In this WP, we will investigate fabrication of alternative TCO layers, with improved performance/cost ratios. The fabrication method on which we focuss is sputtering. In this WP we will develop new TCO layers of single doped or multiple doped oxides based on the elements Sn, Zn and In which have lower cost, high work function and high environmental stability. Usage of Cadmium will be excluded due to EHS (environmental, health and safety) issues. Further, we will investigate multilayer TCOs based on single doped or multiple doped Oxides based on the elements Sn, Zn and In combining higher resistance against moisture and graded work-function to improve current collection. The materials will undergo optical, electrical and climate chamber tests as single layers and integrated in solar cells.

Finally we will up-scale the results from lab-scale (with planar sputter targets) to industrial scale processing (with rotary sputter targets) in WP6.

Work package 5: High efficiency devices

The proof of the functionality of the materials and methods developed in the previous work packages has to come through demonstration of solar cells with improved efficiencies. In this work package we will investigate fabrication of state-of-the art a-Si, mc-Si and micromorph a-Si/mc-Si tandem solar cells on low T plastic substrates (compatible with PEN/PET foils) and on metallic foils with imprinted structure on the insulator. The devices will incorporate the best interfaces, light trapping structures, silicon layers and TCO layers developed in the previous work packages.

The main targets of WP5 are:

  1. single junction solar cells with stable active area efficiencies higher than 8.5% both on plastic and metal foils.
  2. Tandem solar cells with stable active area efficiencies higher than 11% both on plastic and metal foils.

Work package 6: Integration and industrial implementation

The aim of this work package is to transfer the lab-scale results, obtained in the other work packages, to an industrial pilot scale production. This work will be carried out by VHF for the PEN-foil route and by ECN for the metal foil route.

Important sub-tasks in this Work package are upscaling of the embossing processes and the sputtering processes. Last but not least, we will perform an extensive economical and life cycle analysis of a thin film silicon solar cell and module fabrication process, according to the processes developed in the project.