The new PV module technologies using high efficiency solar cells are sensible to UV irradiation, leading to efficiency losses at medium/long terms. Among those technologies, silicon heterojunction solar cells (SHJ) are particularly sensible due to the presence of amorphous/nanocrystalline hydrogenated silicon layers. Indeed, short wavelength UV photons have sufficient energy to break Si-H bonds in those selective layers. Their degradation induces passivation losses at the c-Si/a-Si:H interfaces, leading inevitably to efficiency losses.
For the moment, UV induced degradation (UVID) approaches are adressed at the module level, using encapsulant which block, absorb or convert UV photons before they reach the solar cell. However, those encapsulants reduce the number of photons reaching the cell, and tend to yellow after prolonged UV irradiation, both phenomenon leading to current losses.
This PhD aims at developping approaches at the cell level to mitigate UVID. Two main approaches will be investigated:
- increasing the UV resistance of selective layers by modifying their structure;
- Adding thin layers (deposited on the cells) that block UV photons before they reach the selective layers and/or limits hydrogen migration.
In link with both approaches, the PhD student will study hydrogen migration phenomenons and their impact on the device, with reference cells and with the new developped mitigation methods.
Thanks to the colaboration between CEA-INES and ICube, the PhD student will have access both to industrial and lab scale equipments allowing to explore many different solutions. Characterization tools from both institues will also be accessible, in particular ToF-ERDA for hydrogen migration imaging. Lastly, UV exposure chambers will be used to assess the robustness of the developed solutions.