Extraction of light trapped due to total internal reflection using porous high refractive index nanoparticle films

Mao, Peng; Sun, Fangfang; Yao, Hanchao; Chen, Jing; Zhao, Bo; Xie, Bo; Han, Min; Wang, Guanghou

doi:10.1039/c4nr01065e

Cited by 40 publications

(39 citation statements)

References 45 publications

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“…Porous titanium dioxide (TiO 2 ) bi-layers with different refractive indices were prepared by oblique angle deposition (OAD) [8][9][10][11][12][13] and directly employed on top of III-V semiconductor TJ solar cells with stacks of Ga 0.5 In 0.5 P/GaAs/Ge. Porous titanium dioxide (TiO 2 ) bi-layers with different refractive indices were prepared by oblique angle deposition (OAD) [8][9][10][11][12][13] and directly employed on top of III-V semiconductor TJ solar cells with stacks of Ga 0.5 In 0.5 P/GaAs/Ge.…”

Section: Introductionmentioning

confidence: 99%

“…18,19 The net photocurrent in the Ga 0.5 In 0.5 P/GaAs/Ge TJ solar cell is determined by the generated photocurrent in the Ga 0.5 In 0.5 P top cell or GaAs middle cell. 11 The optimum thicknesses of TiO 2 bi-layer ARCs for the three representative types of TJ solar cells are presented in Table 2. For this reason, i.e., current mismatching, the TiO 2 bi-layer ARC should be optimized to maximize the photon absorption both in the Ga 0.5 In 0.5 P top cell and GaAs middle cell in order to enhance the net photocurrent, and thus improve the PCE of the TJ solar cell.…”

Section: Introductionmentioning

confidence: 99%

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A single-material graded refractive index layer for improving the efficiency of III–V triple-junction solar cells

et al. 2015

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We present a single-material titanium oxide (TiO 2 ) bi-layer antireflection coating (ARC) produced using oblique angle deposition for improving the power conversion efficiency (PCE) of III-V compound semiconductor triple-junction (TJ) solar cells. Experimental demonstration of the porous TiO 2 layers and optical modelling by rigorous coupled-wave analysis indicate that bi-layer TiO 2 could be used as universal ARC for all known TJ stacks with various material combinations. The optimum TiO 2 bi-layer ARC produced on a Ga 0.5 In 0.5 P/GaAs/Ge TJ solar cell exhibits considerably enhanced PCE of 31.6%, which is higher than that of the cells without ARC (23.8%) and with TiO 2 single-layer ARC (29.1%).Incident angle-dependent device characteristics of the fabricated TJ solar cells are also discussed.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A single-material graded refractive index layer for improving the efficiency of III–V triple-junction solar cells

et al. 2015

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“…After determining the refractive index of the 500 nm thick sample, the refractive index of the porous region in the 1700 nm thick sample is to be calculated. The effective medium theory can provide approximate expressions for the effective refractive index of a composite layer such as, ITO and air in this case, based upon the assumption that the feature size in the composite layer is smaller than the wavelength of light When the bulk ITO has the refractive index, n ITO_bulk , and the pores are filled with air of refractive index, n air , the Lorentz–Lorenz relation yields the effective refractive index, n eff , as a solution of

f (n_{eff}) = p \cdot f (n_{air}) + (1 - p) \cdot f (n_{ITO_bulk})

where, f( n ) = ( n 2 − 1)/( n 2 + 2), and p is the porosity of the medium . The refractive indices determined by ellipsometry for the ITO thin film and the ITO‐NT samples prepared at thicknesses of 500 and 1700 nm along with the corresponding values of the calculated porosities are summarized in Table 1 .…”

Section: Fabrication and Characterization Of Ito Ntsmentioning

confidence: 99%

“…Many approaches have been suggested for mitigating the TIR effect such as, surface texturing, antireflection (AR) coatings, and photonic crystal structures . The top‐down surface texturing techniques using dry or photoelectrochemical etching have demonstrated nearly twofold enhancement in the light output power (LOP) .…”

Section: Introductionmentioning

confidence: 99%

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

Park

Kim

Kang

et al. 2016

Advanced Optical Materials

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the GaN epitaxial layer quality, [8] the light trapping due to the total internal reflection (TIR) still limits the light extraction efficiency (LEE) of GaN. This is caused by the abrupt change in the refractive indices across the interface between GaN (n = 2.5) and the sapphire substrate (n = 1.8) or air (n = 1).Many approaches have been suggested for mitigating the TIR effect such as, surface texturing, [9][10][11][12][13] antireflection (AR) coatings, [14][15][16] and photonic crystal structures. [17,18] The top-down surface texturing techniques using dry or photoelectrochemical etching have demonstrated nearly twofold enhancement in the light output power (LOP). [19] However, these etching techniques have innate limitations for use in lateral LEDs because the top p-GaN layer is so thin (typically less than 200 nm) that the etching process for p-GaN must be exactly controlled to avoid degradation of the GaN LEDs. Therefore, bottom-up approaches such as AR coatings with graded refractive index [20] or photonic crystal structures [21] are typically utilized in the lateral LEDs.ZnO nanostructures are one of the most intensively investigated materials that are integrated on the surface of the LEDs for reducing the TIR without compromising the electrical properties. Various morphologies of ZnO nanostructures such as, nanorods (NR), nanowires, and hierarchical 3D nanostructures, typically grown by a hydrothermal technique, were suggested for enhancing the LEE of GaN LEDs. [22][23][24][25] Although the effective refractive index (n air = 1 < n < n ZnO_bulk = 2.0) of Recently, 3D nanostructures have attracted much interest because of their interesting electrical/optical properties such as wave guiding modes, light scattering, antireflection effects, etc. In this work, a facile yet efficient method for the fabrication of hierarchical 3D indium tin oxide (ITO) nanotrees (NTs) and their integration in GaN-based blue-light-emitting diodes (LEDs) for efficient light-extraction are reported. The ITO NTs are fabricated by the obliqueangle (≈85°) deposition method at 240 °C using electron-beam evaporation. The ITO NTs grow via a self-catalytic vapor-liquid-solid mechanism with the branches having an epitaxial relationship with the trunks. The ITO NTs successively deposited on an ITO thin film as a p-contact layer are annealed at 600 °C for 1 min under ambient air in order to form a transparent ohmic contact. The indium gallium nitrde/gallium nitride (InGaN/GaN) LED with ITO NTs presents a 29.5% enhancement in the light output power at an injection current of 20 mA, compared to the reference LED with an ITO thin film p-contact. This enhancement is ascribed to the effective light extraction of the ITO NTs due to to the gradually decreasing profile of the refractive index from 2.08 (ITO thin film), 1.15 (dense ITO NTs), 1.06 (porous ITO NTs) to 1.0 (air). These results are in good agreement with the optical simulation by the COMSOL wave optics module.Figure 7. Light beam profile images of a) the reference and b) ITO-NT-integrate...

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“…Organic light emitting diode (OLED) displays, OLED and LED lighting, antireflective coatings, and microlens component industries have focused on high refractive index (n) materials and their films for the effective use of optical sources [1][2][3][4][5][6]. In particular, transparent films with a high refractive index as well as surface evenness are essential to effectively extract light in OLED lighting and display applications [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Highly smooth and refractive films fabricated from titanium oxide hydrate solution

et al. 2015

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Extraction of light trapped due to total internal reflection using porous high refractive index nanoparticle films

Cited by 40 publications

References 45 publications

A single-material graded refractive index layer for improving the efficiency of III–V triple-junction solar cells

A single-material graded refractive index layer for improving the efficiency of III–V triple-junction solar cells

3D Hierarchical Indium Tin Oxide Nanotrees for Enhancement of Light Extraction in GaN‐Based Light‐Emitting Diodes

Highly smooth and refractive films fabricated from titanium oxide hydrate solution

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