Rear-emitter silicon heterojunction solar cells with atomic layer deposited ZnO:Al serving as an alternative transparent conducting oxide to In2O3:Sn

https://doi.org/10.1016/j.solmat.2019.109953Get rights and content
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Highlights

  • High-efficiency Si heterojunction solar cells with ZnO:Al as a TCO.

  • Soft ALD deposition of ZnO:Al enables mitigation of chemical passivation losses.

  • Rear-emitter cell design enables mitigation of the field-effect passivation losses.

  • Rear-emitter cell design enables mitigation of the transparency-resistivity tradeoff.

  • Replacement of In2O3:Sn by ZnO:Al as front or back TCO without efficiency loss.

Abstract

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 photocurrent 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.

Keywords

Transparent conducting oxide
Silicon heterojunction solar cell
Rear emitter solar cell
Zinc oxide
Atomic layer deposition

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Present address: Empa (Swiss Federal Laboratories for Materials Science and Technology), Feuerwerkerstrasse 39, 3602 Thun, Switzerland. Email: [email protected]