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Numerical and experimental investigation of light trapping effect of nanostructured diatom frustules.

Chen X, Wang C, Baker E, Sun C - Sci Rep (2015)

Bottom Line: In contrast, diatoms, the most common type of phytoplankton found in nature, may offer a very attractive solution.In simulation, placing the diatom frustules on the surface of the light-absorption materials is found to strongly enhance the optical absorption over the visible spectrum.The absorption spectra are also measured experimentally and the results are in good agreement with numerical simulations.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208, USA.

ABSTRACT
Recent advances in nanophotonic light-trapping technologies offer promising solutions in developing high-efficiency thin-film solar cells. However, the cost-effective scalable manufacturing of those rationally designed nanophotonic structures remains a critical challenge. In contrast, diatoms, the most common type of phytoplankton found in nature, may offer a very attractive solution. Diatoms exhibit high solar energy harvesting efficiency due to their frustules (i.e., hard porous cell wall made of silica) possessing remarkable hierarchical micro-/nano-scaled features optimized for the photosynthetic process through millions of years of evolution. Here we report numerical and experimental studies to investigate the light-trapping characteristic of diatom frustule. Rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods are employed to investigate the light-trapping characteristics of the diatom frustules. In simulation, placing the diatom frustules on the surface of the light-absorption materials is found to strongly enhance the optical absorption over the visible spectrum. The absorption spectra are also measured experimentally and the results are in good agreement with numerical simulations.

No MeSH data available.


Simulated absorption spectra of the simplified diatom frustule model with the 50 nm thick active layer in direct contact with (a) the internal plate and (b) cribellum layer, corresponding to case 1 and case 2. The cases of multi layers with homogenized effective refractive index on top of the active layer are used as control cases, corresponding to case 1 and case 2. The case of bare active layer is used as the reference. The enhancement is defined as the ratio of the absorption efficiency between the model with frustule cases (or control cases) and the reference.
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f3: Simulated absorption spectra of the simplified diatom frustule model with the 50 nm thick active layer in direct contact with (a) the internal plate and (b) cribellum layer, corresponding to case 1 and case 2. The cases of multi layers with homogenized effective refractive index on top of the active layer are used as control cases, corresponding to case 1 and case 2. The case of bare active layer is used as the reference. The enhancement is defined as the ratio of the absorption efficiency between the model with frustule cases (or control cases) and the reference.

Mentions: Numerical simulations are performed to first evaluate the contribution to the light trapping effect from each constituting layer of the diatom frustule. RCWA simulated absorption spectra of the thin-film solar cell model with individual constituting layer, including cribellum, cribrum, and internal plate, are shown in Fig. 2(b–d), respectively. In the control cases, the individual layer is represented as the homogenized dielectric layer constituting the effective refractive index (method to calculate the effective refractive index can be found in Supplementary Information). A bare PTB7:PC71BM layer is used as the reference case and the enhancement factor is defined as the calculated light absorption from individual constituting layer normalized by the reference case. Wavelength dependent response can be clearly resolved in Fig. 2, which is due to the distinctly different periodicity and hole size of each layer. As shown in Fig. 2(b), no obvious absorption peak is found in the cribellum layer. In addition, almost identical absorption spectra can be obtained from the corresponding control case using effective index. As the periodicity of the cribellum layer is significantly smaller than the wavelength of sunlight, the scattered field is predominantly evanescent within the target visible spectrum. Thus, the simulation results suggest that the deep sub-wavelength features of cribellum layer do not contribute significantly to the light trapping effect at visible frequencies and its optical property can be represented using the effective media. The limited enhancement is due to the reduced reflection at the surface on the effective media with the lowered effective refractive index. In contrast, a pronounced enhancement peak centered at 390 nm is found in the cribrum layer (Fig. 2(c)), and a wider peak centered at 750 nm is observed in the internal plate in Fig. 2(d) by comparing to the corresponding control cases. These two peaks can be attributed to scattering by the periodic pattern rather than the contribution of the anti-reflection effect from individual layers4243. Therefore, as shown in Fig. 3(a), the diatom frustule is modeled as a stacked system containing cribellum, cribrum and the internal plate, in which the cribellum layer is represented by the homogenized dielectric layer with effective refractive index to save computing resource.


Numerical and experimental investigation of light trapping effect of nanostructured diatom frustules.

Chen X, Wang C, Baker E, Sun C - Sci Rep (2015)

Simulated absorption spectra of the simplified diatom frustule model with the 50 nm thick active layer in direct contact with (a) the internal plate and (b) cribellum layer, corresponding to case 1 and case 2. The cases of multi layers with homogenized effective refractive index on top of the active layer are used as control cases, corresponding to case 1 and case 2. The case of bare active layer is used as the reference. The enhancement is defined as the ratio of the absorption efficiency between the model with frustule cases (or control cases) and the reference.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496668&req=5

f3: Simulated absorption spectra of the simplified diatom frustule model with the 50 nm thick active layer in direct contact with (a) the internal plate and (b) cribellum layer, corresponding to case 1 and case 2. The cases of multi layers with homogenized effective refractive index on top of the active layer are used as control cases, corresponding to case 1 and case 2. The case of bare active layer is used as the reference. The enhancement is defined as the ratio of the absorption efficiency between the model with frustule cases (or control cases) and the reference.
Mentions: Numerical simulations are performed to first evaluate the contribution to the light trapping effect from each constituting layer of the diatom frustule. RCWA simulated absorption spectra of the thin-film solar cell model with individual constituting layer, including cribellum, cribrum, and internal plate, are shown in Fig. 2(b–d), respectively. In the control cases, the individual layer is represented as the homogenized dielectric layer constituting the effective refractive index (method to calculate the effective refractive index can be found in Supplementary Information). A bare PTB7:PC71BM layer is used as the reference case and the enhancement factor is defined as the calculated light absorption from individual constituting layer normalized by the reference case. Wavelength dependent response can be clearly resolved in Fig. 2, which is due to the distinctly different periodicity and hole size of each layer. As shown in Fig. 2(b), no obvious absorption peak is found in the cribellum layer. In addition, almost identical absorption spectra can be obtained from the corresponding control case using effective index. As the periodicity of the cribellum layer is significantly smaller than the wavelength of sunlight, the scattered field is predominantly evanescent within the target visible spectrum. Thus, the simulation results suggest that the deep sub-wavelength features of cribellum layer do not contribute significantly to the light trapping effect at visible frequencies and its optical property can be represented using the effective media. The limited enhancement is due to the reduced reflection at the surface on the effective media with the lowered effective refractive index. In contrast, a pronounced enhancement peak centered at 390 nm is found in the cribrum layer (Fig. 2(c)), and a wider peak centered at 750 nm is observed in the internal plate in Fig. 2(d) by comparing to the corresponding control cases. These two peaks can be attributed to scattering by the periodic pattern rather than the contribution of the anti-reflection effect from individual layers4243. Therefore, as shown in Fig. 3(a), the diatom frustule is modeled as a stacked system containing cribellum, cribrum and the internal plate, in which the cribellum layer is represented by the homogenized dielectric layer with effective refractive index to save computing resource.

Bottom Line: In contrast, diatoms, the most common type of phytoplankton found in nature, may offer a very attractive solution.In simulation, placing the diatom frustules on the surface of the light-absorption materials is found to strongly enhance the optical absorption over the visible spectrum.The absorption spectra are also measured experimentally and the results are in good agreement with numerical simulations.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering Department, Northwestern University, Evanston, IL 60208, USA.

ABSTRACT
Recent advances in nanophotonic light-trapping technologies offer promising solutions in developing high-efficiency thin-film solar cells. However, the cost-effective scalable manufacturing of those rationally designed nanophotonic structures remains a critical challenge. In contrast, diatoms, the most common type of phytoplankton found in nature, may offer a very attractive solution. Diatoms exhibit high solar energy harvesting efficiency due to their frustules (i.e., hard porous cell wall made of silica) possessing remarkable hierarchical micro-/nano-scaled features optimized for the photosynthetic process through millions of years of evolution. Here we report numerical and experimental studies to investigate the light-trapping characteristic of diatom frustule. Rigorous coupled wave analysis (RCWA) and finite-difference time-domain (FDTD) methods are employed to investigate the light-trapping characteristics of the diatom frustules. In simulation, placing the diatom frustules on the surface of the light-absorption materials is found to strongly enhance the optical absorption over the visible spectrum. The absorption spectra are also measured experimentally and the results are in good agreement with numerical simulations.

No MeSH data available.