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Inverted Silicon Nanopencil Array Solar Cells with Enhanced Contact Structures

View Article: PubMed Central - PubMed

ABSTRACT

Although three-dimensional nanostructured solar cells have attracted extensive research attention due to their superior broadband and omnidirectional light-harvesting properties, majority of them are still suffered from complicated fabrication processes as well as disappointed photovoltaic performances. Here, we employed our newly-developed, low-cost and simple wet anisotropic etching to fabricate hierarchical silicon nanostructured arrays with different solar cell contact design, followed by systematic investigations of their photovoltaic characteristics. Specifically, nano-arrays with the tapered tips (e.g. inverted nanopencils) are found to enable the more conformal top electrode deposition directly onto the nanostructures for better series and shunt conductance, but its insufficient film coverage at the basal plane would still restrict the charge carrier collection. In contrast, the low-platform contact design facilitates a substantial photovoltaic device performance enhancement of ~24%, as compared to the one of conventional top electrode design, due to the shortened current path and improved lateral conductance for the minimized carrier recombination and series resistance. This enhanced contact structure can not only maintain excellent photon-trapping behaviors of nanostructures, but also help to eliminate adverse impacts of these tapered nano-morphological features on the contact resistance, providing further insight into design consideration in optimizing the contact geometry for high-performance nanostructured photovoltaic devices.

No MeSH data available.


Current density-voltage (J-V) curves of inverted Si nanopencil arrayed solar cells with different top electrode contact design: directly deposited on top of the nanopencil arrays, mesa bar and low-platform configuration.
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f5: Current density-voltage (J-V) curves of inverted Si nanopencil arrayed solar cells with different top electrode contact design: directly deposited on top of the nanopencil arrays, mesa bar and low-platform configuration.

Mentions: Figure 5 illustrates the corresponding photovoltaic performance of inverted nanopencil arrays based solar cell devices with these three different top electrode contact structures, with Table 1 summarized the important device parameters. Similar open-circuit voltage (Voc) values are observed for all these devices since they are processed with the same doping condition and silicon starting substrates for the uniform junction formation. It is obvious that although these tip-tapered nanopencil arrays would lead to a more conformal and continuous top electrode formation, there is still a substantial film coverage issue existed in the basal plane, which is further confirmed with the corresponding top-view optical image (Supporting Information Figure S2), resulting in the inferior charge carrier collection and hence the lowest Jsc of 28.5 mA/cm2 among all contact schemes. Once the nanostructured window layer is separated from the contact region, the Jsc of both mesa bar and low-platform contacts are improved significantly by at least a 20% of enhancement. As compared to the Jsc of 35.3 mA/cm2 of the mesa bar contact, a slightly lower Jsc of 33.6 mA/cm2 of the low-platform contact is obtained, which can be attributed to the severe carrier recombination due to the relatively rough top electrode/silicon interface induced by the device fabrication. This roughness is mainly come from the formation of small cracks between the two deposited metal layers at the hole edges of the nanomesh and the subsequent exposure in the etching solution23. However, the mesa bar contact scheme would inevitably increase the associated series resistance to 3.1 ohm-cm2 as contrasted to the one of 2.3 ohm-cm2 of the low-platform contact because of its longer current path required, approximating the height of the nanopencil, and thus impair its corresponding FF and PCE of the fabricated devices. This longer current path issue is expected to even get worsen for the taller features. In this case, owing to the shortened current path and good lateral conductance, the efficient carrier collection of Jsc being 33.6 mA/cm2 and low series resistance of 2.2 ohm-cm2 are readily achieved for the low-platform contacted device. More importantly, this enhanced contact design can prevent potential shunts from the nanostructured surface and result in a high FF of 0.64, which leads to the highest PCE of 10.8% performed in this work. All these have elucidated the importance of contact design consideration of highly-efficient nanostructure-based solar devices for the optimization of light absorption, carrier collection, leakage elimination and lateral conductance.


Inverted Silicon Nanopencil Array Solar Cells with Enhanced Contact Structures
Current density-voltage (J-V) curves of inverted Si nanopencil arrayed solar cells with different top electrode contact design: directly deposited on top of the nanopencil arrays, mesa bar and low-platform configuration.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037459&req=5

f5: Current density-voltage (J-V) curves of inverted Si nanopencil arrayed solar cells with different top electrode contact design: directly deposited on top of the nanopencil arrays, mesa bar and low-platform configuration.
Mentions: Figure 5 illustrates the corresponding photovoltaic performance of inverted nanopencil arrays based solar cell devices with these three different top electrode contact structures, with Table 1 summarized the important device parameters. Similar open-circuit voltage (Voc) values are observed for all these devices since they are processed with the same doping condition and silicon starting substrates for the uniform junction formation. It is obvious that although these tip-tapered nanopencil arrays would lead to a more conformal and continuous top electrode formation, there is still a substantial film coverage issue existed in the basal plane, which is further confirmed with the corresponding top-view optical image (Supporting Information Figure S2), resulting in the inferior charge carrier collection and hence the lowest Jsc of 28.5 mA/cm2 among all contact schemes. Once the nanostructured window layer is separated from the contact region, the Jsc of both mesa bar and low-platform contacts are improved significantly by at least a 20% of enhancement. As compared to the Jsc of 35.3 mA/cm2 of the mesa bar contact, a slightly lower Jsc of 33.6 mA/cm2 of the low-platform contact is obtained, which can be attributed to the severe carrier recombination due to the relatively rough top electrode/silicon interface induced by the device fabrication. This roughness is mainly come from the formation of small cracks between the two deposited metal layers at the hole edges of the nanomesh and the subsequent exposure in the etching solution23. However, the mesa bar contact scheme would inevitably increase the associated series resistance to 3.1 ohm-cm2 as contrasted to the one of 2.3 ohm-cm2 of the low-platform contact because of its longer current path required, approximating the height of the nanopencil, and thus impair its corresponding FF and PCE of the fabricated devices. This longer current path issue is expected to even get worsen for the taller features. In this case, owing to the shortened current path and good lateral conductance, the efficient carrier collection of Jsc being 33.6 mA/cm2 and low series resistance of 2.2 ohm-cm2 are readily achieved for the low-platform contacted device. More importantly, this enhanced contact design can prevent potential shunts from the nanostructured surface and result in a high FF of 0.64, which leads to the highest PCE of 10.8% performed in this work. All these have elucidated the importance of contact design consideration of highly-efficient nanostructure-based solar devices for the optimization of light absorption, carrier collection, leakage elimination and lateral conductance.

View Article: PubMed Central - PubMed

ABSTRACT

Although three-dimensional nanostructured solar cells have attracted extensive research attention due to their superior broadband and omnidirectional light-harvesting properties, majority of them are still suffered from complicated fabrication processes as well as disappointed photovoltaic performances. Here, we employed our newly-developed, low-cost and simple wet anisotropic etching to fabricate hierarchical silicon nanostructured arrays with different solar cell contact design, followed by systematic investigations of their photovoltaic characteristics. Specifically, nano-arrays with the tapered tips (e.g. inverted nanopencils) are found to enable the more conformal top electrode deposition directly onto the nanostructures for better series and shunt conductance, but its insufficient film coverage at the basal plane would still restrict the charge carrier collection. In contrast, the low-platform contact design facilitates a substantial photovoltaic device performance enhancement of ~24%, as compared to the one of conventional top electrode design, due to the shortened current path and improved lateral conductance for the minimized carrier recombination and series resistance. This enhanced contact structure can not only maintain excellent photon-trapping behaviors of nanostructures, but also help to eliminate adverse impacts of these tapered nano-morphological features on the contact resistance, providing further insight into design consideration in optimizing the contact geometry for high-performance nanostructured photovoltaic devices.

No MeSH data available.