Here high-efficiency (above 21%) large-area silicon heterojunction solar cells with atomic layer deposited ZnO:Al as front- or back-side transparent conducting oxide are demonstrated. Photoconductance decay measurements indicate that the excellent chemical passivation provided by the a-Si:H(i,p) and a-Si:H(i,n) stacks is preserved upon deposition of ZnO:Al, and that field-effect passivation losses for the a-Si:H(i,p)/ZnO:Al contact can be mitigated by lowering the Al doping level. Use of low Al-doping is enabled by the rear-emitter configuration which, in addition to facilitating the a-Si:H(i,p)/ZnO:Al contact engineering, enables a higher photo-current due to the decrease in free-carrier absorption in ZnO:Al. The results encourage the use of In-free transparent conducting oxides in silicon heterojunction solar cells, as the replacement of In2O3:Sn without efficiency loss is demonstrated.
Solar Energy Materials and Solar Cells, vol. 200, p. 5, Sep 2019.