Influence of the microstructure of n-type Si:H and passivation by ultrathin Al2O3 on the efficiency of Si radial junction nanowire array solar cells

• 180 μm thick p-type Si was used to fabricate AZO/Si:H(n)/a-Si:H/c-Si(p) nanowire solar cells.
• JSC was increased by 16.2% when an n-type Si:H layer changed from amorphous to a double phase structure.
• Controlling the Al2O3 thickness played a key role in balancing the passivating and tunneling effects.
• With 0.77-nm-thick Al2O3, JSC and η were increased by 10.2% and 6.8%, respectively.

In this work, p-type solar-grade Si (100) wafers with a thickness of 180 μm were used to fabricate Al-doped ZnO(AZO)/n-type Si:H/i-Si:H/c-Si(p) nanowire (NW) array solar cells in which the Si:H and Al2O3 layers were deposited by plasma-enhanced chemical deposition and atomic layer deposition, respectively. To realize a good coverage of Si:H layers on the Si NWs, excessively thin Si:H layers were avoided. Moreover, since the NW array gives rise to significant light trapping, the light absorption by the Si:H layers could not be neglected. It is known that compared to amorphous Si:H, the charge mobility and light absorption are improved in the two-phase Si:H with nanocrystalline grains dispersed in the amorphous matrix. Therefore, it is important to investigate the influence of the microstructures of n-type Si:H on the performance of solar cells. On the other hand, in contrast to the Al2O3 passivation of planar Si solar cells, in this study, ultrathin Al2O3 layers were deposited on Si NWs without post-deposition annealing. We also discuss the passivation behavior of these ultrathin Al2O3 layers on n-type Si:H and the balance between the surface passivation and the role of these layers as tunnel barriers.

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