The PH2OTOGEN demonstrator uses a photoabsorber layer consisting of organic semiconductor materials to capture light in the H2-evolving photocatalyst sheet. The selected materials are typically used in organic solar cells.
The photoabsorber layer is necessary to generate excited electrons for the reduction of hydrogen from the incident light.
- The organic photoabsorber layer of the PH2OTOGEN demonstrator is in principle very similar to a solar cell.
- Unlike traditional solar cells made from silicon, organic photoabsorbers are special carbon-based materials, called ‘organic semiconductors’ that absorb light and can be processed using ink-based printing.
- When sunlight hits the photoabsorber, it excites the molecules, giving electrons enough energy to move. This energy is then captured and turned into electric current.
- To improve the photoabsorber layer a ‘bulk heterojunction’ is used: Two different materials - one that donates electrons (electron donor) and one that accepts them (electron acceptor) - are blended in a fine mix. This makes it easier to separate and collect the electric charges created by the sunlight.
- Excited electrons at the surface will travel to the catalyst on top and will finally be used in the chemical reduction of H+ ions into an H2 molecule.
Choice of organic semiconductor
The semiconductors are chosen along the following criteria:
- Polymer based on polythiophene as the electron donor in combination with a small molecule acceptor or polymer acceptor
- Material combination with high efficiency and low degradation
- Absorption of light can be adjusted by using different material combinations to enable good synergy with the photoanode layer.
Pascale Chenevrier, Researcher in nanosciences, CEA