Development of a-Si:H/c-Si heterojunctions for the i2-module concept: Low-temperature passivation and emitter formation on wafers bonded to glass

With crystalline silicon technology around in commercial products for over 30 years and still dominating the PV market for the foreseeable future, it is important to consider how this technology can be improved to cope with the increasing demand for lower cost. This paper builds on a concept proposed by imec, integrated-interconnect-module (i2-module), to merge current crystalline silicon cell and module technology with module-level thin-film technology. It investigates, in particular, how hydrogenated amorphous silicon (a-Si:H) layers can be deposited on wafers that are bonded to a glass superstrate, to provide a low-temperature (heterojunction) approach for passivation and emitter formation in this concept.First, the concept is introduced, together with its context and motivation for a-Si:H heterojunctions. Then, the experiments are described. Starting from screening trials on temporarily and permanently bonded wafers, the plasma-enhanced chemical vapor deposition (PECVD) a-Si:H deposition process is optimized by shielding the adhesive from the plasma, resulting in comparable surface passivation quality between bonded samples and standalone wafers. Finally, first attempts toward integration into solar cell devices are reported, resulting into efficiencies above 18%.

► Imec's i2-module concept and motivation is based on module-level cell processing. ► Low-temperature a-Si layers are deposited on wafers bonded to glass. ► Lifetimes of bonded and standalone samples can be comparable. ► Such module-level heterojunctions already yielded devices with >18% efficiency.