HERCULES (High Efficiency Rear Contact Solar Cells and Ultra Powerful ModuLES)

Starting Point

The photovoltaics market is highly competitive at the moment, as Asian competitors are putting increasing pressure on European producers. For it to remain competitive, the European solar industry has to:

  1. reduce production and investment costs in order to hold their own in price wars with competition from emerging industrialised nations such as China or Taiwan,
  2. invest in innovative industrial processes that facilitate combining high efficiency with low production costs, and
  3. develop state-of-the-art tools and processes that are very difficult to replicate in order to secure the technological lead.

These requirements mean that the European industry is faced with a paradox: On the one hand, they have to reduce costs; on the other hand, high-efficiency solar technology requires ever more complex production processes, which lead to increasing investment and production costs. Thus, we are confronted with the Herculean task of producing high-efficiency solar technology using competitive industrial processes.


On the basis of this, we are pursuing the following four main goals with the HERCULES project:

  1. developing ultra-high-efficiency solar modules on a pilot scale (average efficiency >21%),
  2. reducing the complexity of production steps and necessary investments, and decreasing production costs on a pilot scale from their current level of around 0.8–1.0 €/Wp to 0.7 €/Wp
  3. increasing the service life of solar modules to 35 years
  4. providing evidence for the possibility of ultra-high-efficiency solar cells with efficiency of 25% and over


As part of project HERCULES, innovative solar cells will be developed from monocrystalline n-type silicon (c-Si). They will be based on back-contacted solar cells, for which an alternative process shall be used for forming the p–n junction. In addition, other solar cells shall be developed based on this technology that draw on hybrid solar cell concepts (homo- and hetero­junctions), among others. In particular, a combination of the following three concepts will be investigated:

  1. PERT cells (Passivated Emitter, Rear Totally diffused)
    These cells offer the advantage of being compatible with the majority of systems used in p-type production lines nowadays. In order to convert a process based on p-type to one based on n-type cells, only two additional steps are necessary. PERT cells are bifacial and therefore achieve up to 30% higher performance than non-bifacial cells.
  2. IBC cells (Interdigitated Back Contact)
    If all electrical contacts are attached to the back of a cell, there will be no shading losses and the front can be optimised at will. Furthermore, IBC cells offer new possibilities for module wiring.
  3. HET cells (Heterojunction)
    When it comes to heterojunctions from amorphous silicon to crystalline silicon, the wafer surface’s excellent passivation leads to open-circuit voltages (VOC) of over 740 mV. In addition, all production steps can be carried out at temperatures of no more than 250 °C, which makes the HET concept particularly interesting for very thin substrates (100 µm and less).

These concepts are the most promising if you are looking to achieve extremely high efficiency using industrial processes. The HERCULES strategy involves implementing the developed process on an industrial scale in a way that takes into account all important costing factors across the entire production process.

The solar cell concepts developed in project HERCULES should make 25% efficiency possible. As a result, the modules produced as part of our pilot line will have a performance of over 340 Wp. These concepts pave the way for the extremely high efficiency to be achieved by the next generation of c-Si based solar cells.