Transparent Metallic Fractal Electrodes for Semiconductor Devices

Afshinmanesh, Farzaneh; Curto, Alberto G.; Milaninia, Kaveh M.; Hulst, Niek F. van; Brongersma, Mark L.

doi:10.1021/nl501738b

Cited by 67 publications

(41 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Such systematic optimization is not possible for random meshes. Recent work demonstrating such optimization has shown significant absorption enhancements in ultra-thin GaAs layers40, as well as improved optical transmission into photodiodes using 2D fractal patterns41.…”

Section: Resultsmentioning

confidence: 99%

Large-area soft-imprinted nanowire networks as light trapping transparent conductors

Groep

Gupta

Verschuuren

et al. 2015

Sci Rep

View full text Add to dashboard Cite

Using soft-imprint nanolithography, we demonstrate large-area application of engineered two-dimensional polarization-independent networks of silver nanowires as transparent conducting electrodes. These networks have high optical transmittance, low electrical sheet resistance, and at the same time function as a photonic light-trapping structure enhancing optical absorption in the absorber layer of thin-film solar cells. We study the influence of nanowire width and pitch on the network transmittance and sheet resistance, and demonstrate improved performance compared to ITO. Next, we use P3HT-PCBM organic solar cells as a model system to show the realization of nanowire network based functional devices. Using angle-resolved external quantum efficiency measurements, we demonstrate engineered light trapping by coupling to guided modes in the thin absorber layer of the solar cell. Concurrent to the direct observation of controlled light trapping we observe a reduction in photocurrent as a result of increased reflection and parasitic absorption losses; such losses can be minimized by re-optimization of the NW network geometry. Together, these results demonstrate how engineered 2D NW networks can serve as multifunctional structures that unify the functions of a transparent conductor and a light trapping structure. These results are generic and can be applied to any type of optoelectronic device.

show abstract

Section: Resultsmentioning

confidence: 99%

Large-area soft-imprinted nanowire networks as light trapping transparent conductors

Groep

Gupta

Verschuuren

et al. 2015

Sci Rep

View full text Add to dashboard Cite

show abstract

“…For example, in conventional solar cells or photodiodes with front and rear contacts, a nonnegligible fraction of the incoming solar power is immediately lost at the front contact either through absorption, as in the case of transparent conductive oxides or through refl ection at contact grid fi ngers. As a result, many groups have recently proposed design schemes to mitigate front contact losses, such as less absorbing transparent conductive oxides, [4][5][6][7][8] or less refl ective metal contacts such as nanowire grids, [ 9,10 ] fractal contacts, [ 11 ] contacts with different shapes, [12][13][14][15][16] and various other approaches. [17][18][19][20][21] Very high contact transparency usually comes at the expense of reduced conductivity, which in turn leads to series resistance and device electrical losses.…”

Section: Doi: 101002/adom201600252mentioning

confidence: 99%

Effectively Transparent Front Contacts for Optoelectronic Devices

Saive

Borsuk

Emmer

et al. 2016

Advanced Optical Materials

View full text Add to dashboard Cite

COMMUNICATIONshadow loss, and the sheet resistance and absorption losses associated with planar layers that facilitate lateral carrier transport to the grid fi ngers. [ 22,23 ] For high effi ciency silicon heterojunction (HIT) solar cells, contact design requires a trade-off between grid fi nger resistance and the sheet resistance and transmission losses of the transparent conducting oxide (TCO)/ amorphous silicon structures coating the cell front surface. [ 24 ] In this paper, we describe a new front contact design principle that overcomes both shadowing losses and parasitic absorption without reducing the conductivity. By redirecting the scattered light incident on the front contact to the solar cell active absorber layer surface, micrometer-scale triangular crosssection grid fi ngers can perform as effectively transparent and highly conductive front contacts. Previously, researchers have designed light harvesting strings that serve to obliquely refl ect light, which is then redirected into the cell by total internal refl ection from the encapsulation layers. [ 16 ] By contrast our front contact design does not require total internal refl ection at the encapsulation layer. Furthermore in our design, the contact fi ngers are micrometer sized and can be placed very close together such that a TCO with reduced thickness can be used-and in some cases the TCO layer might possibly be omitted completely. We demonstrate with simulations and experimental results that designs utilizing effectively transparent triangular cross-section grid fi ngers rather than conventional front contacts have the potential to provide 99.86% optical transparency while ensuring effi cient lateral transport corresponding to a sheet resistance of 4.8 Ω sq −1 due to their close spacing of only 40 µm. Thus effectively transparent contacts have potential as replacements for both the front grid and TCO layer used, e.g., in HIT solar cells. While related schemes for contacts were envisioned early in the development of photovoltaics technology, [ 25 ] they have not found application in current photovoltaic technology, which is increasingly dominated by high effi ciency silicon photovoltaics. Moreover, the effectively transparent front contact design is conceptually quite general and applicable to almost any other front-contacted solar cell or optoelectronic device. For example, we obtained similar experimental results when applying our structures to InGaP-based solar cells.Figure 1 a,b shows the steady-state electric fi eld magnitude distribution of a freestanding triangular contact and a fl at contact, respectively, with 550 nm monochromatic plane wave illumination normally incident at the top of the simulation cell. For planar grid fi ngers, part of the incident light is refl ected back toward the incidence direction, as is apparent from the high electric fi eld density above the contact plane. By contrast, the triangular cross-section grid fi nger does not exhibit a similar back refl ection, as indicated by the lack of an increased electric

show abstract

“…Unfortunately, the transparency of these metal nanostructures is often below 80%, depending on the metallic feature size [20,21]. Nevertheless, the unique opto-electronic properties of metallic nanostructures can make them less reflective than expected from their surface coverage [22,23]. Taking this concept one step further, cloaking of metals in metamaterials has been proposed [24,25,26].…”

Section: Introductionmentioning

confidence: 99%

Optical Design of Textured Thin-Film CIGS Solar Cells with Nearly-Invisible Nanowire Assisted Front Contacts

2017

View full text Add to dashboard Cite

The conductivity of transparent front contacts can be improved by patterned metallic nanowires, albeit at the cost of optical loss. The associated optical penalty can be strongly reduced by texturization of the cell stack. Remarkably, the nanowires themselves are not textured and not covered in our design. This was shown by optical modeling where the width of the nanowire, the texture height and the texture period were varied in order to obtain a good insight into the general trends. The optical performance can be improved dramatically as the reflection, which is the largest optical loss, can be reduced by 95% of the original value. The spectra reveal absorption in the Cu(In,Ga)Se2 (CIGS) layer of 95% and reflection below 2% over a large part of the spectrum. In essence, a virtually black CIGS cell stack can be achieved for textured cells with a metal nanogrid. Moreover, it turned out that the ratio between the width of the nanowire and the height of the texture is a critical parameter for optical losses.

show abstract

Transparent Metallic Fractal Electrodes for Semiconductor Devices

Cited by 67 publications

References 32 publications

Large-area soft-imprinted nanowire networks as light trapping transparent conductors

Large-area soft-imprinted nanowire networks as light trapping transparent conductors

Effectively Transparent Front Contacts for Optoelectronic Devices

Optical Design of Textured Thin-Film CIGS Solar Cells with Nearly-Invisible Nanowire Assisted Front Contacts

Contact Info

Product

Resources

About