Kwang-Chang Lai

Efficiency Enhancement of InGaN-Based Multiple Quantum Well Solar Cells Employing Antireflective ZnO Nanorod Arrays

Antireflective ZnO nanorod arrays (NRAs) by a scalable chemical method have been applied for InGaN-based multiple quantum well solar cells. The length of the NRAs plays an important role in photovoltaic characteristics. It was found that the 1.1-μm-long NRA results in enhanced conversion efficiency due to the suppressed surface reflection. However, the 2.5- μm-long NRAs, although exhibiting the lowest reflection, lead to slightly deteriorated performances, possibly due to the increased absorption of the NRAs. The results indicate that the absorption of lengthened NRAs should be considered when optimizing their antireflection performances. We demonstrated a viable efficiency-boosting way for photovoltaics.

Synthesis of anti-reflective and hydrophobic Si nanorod arrays by colloidal lithography and reactive ion etching

Si nanorod arrays (NRAs) mimicking moth-eye structures were fabricated with colloidal lithography and reactive ion etching. Compared with that on polished surface, the reflectance on NRA structures is significantly reduced by more than 10 times. The reflectance is decreased with the height of the NRAs. The anti-reflection (AR) ability of the NRAs is accompanied with broad band, omnidirectional, and polarization-insensitive characteristics. The enhancement of surface hydrophobicity is also observed with increasing height of the NRAs. A detailed experimental analysis of the height-dependent AR and self-cleaning characteristics will benefit the design and optimization processes of Si nanowire-based optoelectronic devices.

Origin of Hot Carriers in InGaN-Based Quantum-Well Solar Cells

InxGa1-xN/GaN multiple quantum-well (QW) (MQW) solar cells with x = 0.30 and 0.15 were characterized. The MQWs with x = 0.30 show deteriorated performances due to the inferior crystal qualities. At the temperatures above 200 K, the conversion efficiency (η) for x = 0.30 exhibits an abrupt increase led by the thermally activated carriers. Two potential origins are proposed for the hot carriers: 1) the native shallow donors in the MQWs and 2) the shallow QWs due to the compositional fluctuations. According to the distinct behavior of the device with x = 0.15, it is believed that the shallow QWs lead to the abrupt increase in η.

Efficiency enhancement of InGaN multi-quantum-well solar cells via light-harvesting SiO2 nano-honeycombs

Periodic sub-wavelength SiO2 nano-honeycombs are fabricated on GaN-based multiple quantum well solar cells by self-assembly polystyrene nanosphere lithography and reactive ion etching. The nano-honeycombs are found to be effective in suppressing the undesired surface reflections over a wide range of wavelengths. Under the illumination of air mass 1.5G solar simulator, conversion efficiency of the solar cell is enhanced by 24.4%. Simulations based on finite-difference time-domain method indicate that the improved performances result from the enhanced optical absorption in the active region due to the reflection suppression and enhanced forward scattering.

Determination of the neutrino flavor ratio at the astrophysical source

We discuss the reconstruction of neutrino flavor ratios at astrophysical sources through the future neutrino-telescope measurements. Taking the ranges of neutrino mixing parameters

Flavor transition mechanisms of propagating astrophysical neutrinos: A model independent parametrization

{\ensuremath{\theta}}_{ij}

NEUTRINO FLAVOR RATIOS ON THE EARTH FOR DECAY AND OSCILLATION SCENARIOS

as those given by the current global fit, we demonstrate by a statistical method that the accuracies in the measurements of energy-independent ratios

Probing Flavor Transition Mechanisms of Astrophysical Neutrinos

R\ensuremath{\equiv}\ensuremath{\phi}({\ensuremath{\nu}}_{\ensuremath{\mu}})/(\ensuremath{\phi}({\ensuremath{\nu}}_{e})+\ensuremath{\phi}({\ensuremath{\nu}}_{\ensuremath{\tau}}))

Classifying and probing flavor transition mechanisms of astrophysical high energy neutrinos

and

COSMOGENIC TAU NEUTRINO INDUCED RADIO EMISSION

S\ensuremath{\equiv}\ensuremath{\phi}({\ensuremath{\nu}}_{e})/\ensuremath{\phi}({\ensuremath{\nu}}_{\ensuremath{\tau}})