Morales-Vilches, A.B.; Larionova, Y.; Wietler, T.; Cruz, A.; Korte, L.; Peibst, R.; Brendel, R.; Schlatmann, R.; Stannowski, B.: ZnO:Al/a-SiOx front contact for polycrystalline-silicon-on-oxide (POLO) solar cells. AIP Conference Proceedings 1999 (2018), p. 040016/1-6
Polycrystalline-silicon-on-oxide (POLO) junctions and related contacting schemes have shown their capability to facilitate high efficiencies for solar cells with passivating selective contacts [1-3]. In this work the front contacting of two-side contacted POLO cells with sputtered aluminum-doped zinc oxide (ZnO:Al) has been investigated. Different approaches were followed to obtain good lifetimes in cell precursors and keep high Voc values in finished cells. Degradation in minority carrier lifetime and implied Voc (iVoc) was observed after the ZnO:Al sputtering deposition. In order to recover the passivation, various thermal treatments were applied. The necessity to implement a protecting layer to cap the ZnO:Al/poly-Si structures during the annealing treatment to prevent a fill factor degradation in finished cells was observed. Initially an intrinsic a-Si:H layer was used as a temporary protecting layer. However, during the decapping process, to remove the amorphous layer, lifetime and iVoc are significantly degraded. Therefore a permanent a-SiOx protecting layer was implemented for maintaining good passivation (Voc = 710 mV). This layer has the additional benefit of improving the optical (AR) behaviour on finished cells (increasing Jsc by 1.5%). The best cell reached a conversion efficiency of 21.7 %.