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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.


(a) Current density-voltage (J-V) curves of Si nanostructure arrayed solar cells with top electrode contact directly deposited on the top. (b) The corresponding angle-dependent short-circuit current density and (c) photovoltaic conversion efficiency of these Si nanostructured devices.
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f3: (a) Current density-voltage (J-V) curves of Si nanostructure arrayed solar cells with top electrode contact directly deposited on the top. (b) The corresponding angle-dependent short-circuit current density and (c) photovoltaic conversion efficiency of these Si nanostructured devices.

Mentions: Once the conformality of the top electrode stack is assessed, it is important to evaluate their corresponding effect on the photovoltaic device performance of all nano-arrayed solar cell devices. Notably, even though these solar devices are not optimized for their best efficiency, their geometrical parameters, except for the morphology, and fabrication conditions (e.g. sputtered top electrodes) are maintained the same for all samples studied in this work for the fair comparison. Figure 3a illustrates the photovoltaic properties of all different types of nano-arrayed cells measured under AM 1.5 G (i.e. 1000 W/m2 at 25 °C) at the normal incident angle. Obviously, all these devices display the similar open-circuit voltage (Voc) of ~0.53 V and fill factors (FF) of ~0.58 but with the remarkable difference in the short-circuit current (Jsc) and PCE. In specific, the nanopencil arrayed cell exhibits the highest Jsc of 28.5 mA/cm2 and PCE of 8.7% among all devices. Furthermore, as shown in Fig. 3b,c, the nanopencil cell also demonstrates the excellent omnidirectional characteristics, maintaining over 95% and 80% of their PCEs for the incident angle up to 40° and 60°, respectively, which has nearly 20% of improvement in PCE and Jsc over the conventional nanopillar devices. All these significant enhancements can be attributed to the excellent light absorption characteristics for the effective photo-carrier generation as well as the better top electrode coverage directly deposited on the tip-tapered nanostructures for the efficient carrier collection as discussed above. Based on the previous optical study19, although the nanopencil arrays have been revealed to suppress the optical reflection well below 5% over the solar spectrum and the wide angle of incidence between 0° and 60°, the same performance in PCE and Jsc are not observed for the fabricated solar devices here, suggesting that the top electrode coverage in the basal plane of nano-arrays is still not compact and continuous enough for the minimization of contact resistance. Importantly, the increased interfacial area of the contact region could badly deteriorate the charge collection efficiency of these 3-D nanostructure-based solar devices due to the significant surface/interface recombination2730. In this case, in order to further depress and eliminate the undesired recombination effect, an alternative design on the contact structure is essentially required for the devices.


Inverted Silicon Nanopencil Array Solar Cells with Enhanced Contact Structures
(a) Current density-voltage (J-V) curves of Si nanostructure arrayed solar cells with top electrode contact directly deposited on the top. (b) The corresponding angle-dependent short-circuit current density and (c) photovoltaic conversion efficiency of these Si nanostructured devices.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: (a) Current density-voltage (J-V) curves of Si nanostructure arrayed solar cells with top electrode contact directly deposited on the top. (b) The corresponding angle-dependent short-circuit current density and (c) photovoltaic conversion efficiency of these Si nanostructured devices.
Mentions: Once the conformality of the top electrode stack is assessed, it is important to evaluate their corresponding effect on the photovoltaic device performance of all nano-arrayed solar cell devices. Notably, even though these solar devices are not optimized for their best efficiency, their geometrical parameters, except for the morphology, and fabrication conditions (e.g. sputtered top electrodes) are maintained the same for all samples studied in this work for the fair comparison. Figure 3a illustrates the photovoltaic properties of all different types of nano-arrayed cells measured under AM 1.5 G (i.e. 1000 W/m2 at 25 °C) at the normal incident angle. Obviously, all these devices display the similar open-circuit voltage (Voc) of ~0.53 V and fill factors (FF) of ~0.58 but with the remarkable difference in the short-circuit current (Jsc) and PCE. In specific, the nanopencil arrayed cell exhibits the highest Jsc of 28.5 mA/cm2 and PCE of 8.7% among all devices. Furthermore, as shown in Fig. 3b,c, the nanopencil cell also demonstrates the excellent omnidirectional characteristics, maintaining over 95% and 80% of their PCEs for the incident angle up to 40° and 60°, respectively, which has nearly 20% of improvement in PCE and Jsc over the conventional nanopillar devices. All these significant enhancements can be attributed to the excellent light absorption characteristics for the effective photo-carrier generation as well as the better top electrode coverage directly deposited on the tip-tapered nanostructures for the efficient carrier collection as discussed above. Based on the previous optical study19, although the nanopencil arrays have been revealed to suppress the optical reflection well below 5% over the solar spectrum and the wide angle of incidence between 0° and 60°, the same performance in PCE and Jsc are not observed for the fabricated solar devices here, suggesting that the top electrode coverage in the basal plane of nano-arrays is still not compact and continuous enough for the minimization of contact resistance. Importantly, the increased interfacial area of the contact region could badly deteriorate the charge collection efficiency of these 3-D nanostructure-based solar devices due to the significant surface/interface recombination2730. In this case, in order to further depress and eliminate the undesired recombination effect, an alternative design on the contact structure is essentially required for the devices.

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.