Aluminium metallisation for interdigitated back-contact silicon heterojunction solar cells

Abstract

Back-contact silicon heterojunction solar cells with an efficiency of 22% were manufactured, featuring a simple aluminium metallisation directly on the doped amorphous silicon films. Both the open-circuit voltage and the fill factor heavily depend on the parameters of the annealing step after aluminium layer deposition. Using numerical device simulations and in accordance with the literature, we demonstrate that the changes in solar cell parameters with annealing can be explained by the formation of an aluminium silicide layer at temperatures as low as 150°C, improving the contact resistance and thus enhancing the fill factor. Further annealing at higher temperatures initialises the crystallisation of the amorphous silicon layers, yielding even lower contact resistances, but also introduces more defects, diminishing the open-circuit voltage.

A novel silicon heterojunction IBC process flow using partial etching of doped a‐Si:H to switch from hole contact to electron contact in situ with efficiencies close to 23%

“…Such differences across a device are not expected to have a strong impact on device performance. Obviously, the absolute thickness variation would increase with increase in etch time if thicker p + a‐Si:H layers would be used, but typical p + a‐Si:H layers used for HJ IBC devices are below 20 nm . This reduced etch rate in patterned areas was taken into account during device fabrication by increasing the etch duration accordingly.…”