Silicon heterojunction interdigitated back-contact solar cells bonded to glass with efficiency >21%

- A lift-off method using a sacrificial SiOx layer is implemented for emitter patterning.
- Two bonding adhesives, silicone and ethylene vinyl acetate, are evaluated at cell level.
- Comparable lifetimes and Voc are achieved on reference freestanding and bonded solar cells.
- Silicone-bonded SHJ-IBC cells with Voc of 734 mv and efficiency of 21.7% are obtained.
- Thermal anneals performed on the finished cells yield a significant improvement of the fill factor by reducing the series resistance.

Previously, IMEC proposed the i2-module concept which allows to process silicon heterojunction interdigitated back-contact (SHJ-IBC) cells on thin (<50 µm) Si wafers at module level. This concept includes the bonding of the thin wafer early on to the module cover glass, which delivers mechanical support to the wafer and thus significantly improves the production yield. In this work, we test silicone and ethylene vinyl acetate bonding agents and prove them to be resistant to all rear side processes, including wet and plasma processes. Moreover, a lift-off process using a sacrificial SiOx layer has been developed for emitter patterning to replace conventional lithography. The optimized process steps are demonstrated by the fabrication of SHJ-IBC cells on 6-inch 190 µm-thick wafers. Efficiencies up to 22.6% have been achieved on reference freestanding wafers. Excellent Voc of 734 mv and Jsc of 40.8 mA/cm2 lead to an efficiency of 21.7% on silicone-bonded cells, where the high Voc indicates the process compatibility of the bonding agent. The developments that enabled such achievements and the key factors that limit the device performance are discussed in this paper.