Moth-eye Pattern Research Articles

Nanostructured broadband antireflection coatings on AlInP fabricated by nanoimprint lithography

We report the fabrication of moth-eye antireflection nanostructures on AlInP compound commonly used as a window layer in high-efficiency multijunction solar cells. The broadband antireflective nanostructures were fabricated by nanoimprint lithography directly on molecular beam epitaxy grown AlInP/GaAs surface. At normal incidence, the structures exhibited an average reflectivity of 2.7% measured in a spectral range 450–1650 nm. Photoluminescence measurements of the emission from GaAs substrate suggest that the optical losses associated with the moth-eye pattern are low. Nanoimprint lithography offers a cost-effective approach to fabricate broadband antireflection coatings required in III–V high-efficiency multijunction solar cells.

Enhanced performance of solar cells with anti-reflection layer fabricated by nano-imprint lithography

Because of increase in demand for clean energy sources, photovoltaic device is becoming more important as a new power plant. To replace fossil fuels with photovoltaics, generating electricity with solar cells should meet cost effectiveness and high efficiency. An anti-reflection technique is one of the effective methods to achieve high efficiency. To reduce the reflection at the surface of concentrated photovoltaic device, a nanometer scale dot-pattern array was formed on the surface of GaInP/Ga(In)As/Ge solar cells by nano-imprint lithography. Since this nano-pattern is smaller than the wavelength of visible light, the effective refractive index near the surface changes gradually. Thus, the reflection of the light at the surface with moth-eye structure can be effectively reduced for overall spectral region. As a result, a solar cell with the moth-eye pattern as an anti-reflection layer showed lower reflectance and enhanced total conversion efficiency, compared to a solar cell without a moth-eye patterned layer. The patterned solar cell was characterized using UV–vis spectrophotometer, atomic force microscope (AFM) and scanning electron microscope (SEM), and its total conversion efficiency was measured by solar simulator.

Imprinted Moth-Eye Antireflection Patterns on Glass Substrate

Sub-micron sized, conical shaped moth-eye structure was transferred to thermoplastic polymer film, such as polyvinyl chloride (PVC) using hot embossing process. Since master template was made of polycarbonate, embossing temperature and pressure were carefully maintained to 100°C and 10 atm. Conical shaped moth-eye pattern was reversed to tapered hole pattern on PVC film. Hot embossed PVC film was then used as transparent template for subsequent UV nanoimprint process, in order to form the conical shaped sub-micron moth-eye structure on glass substrate. After thin layer of Si oxide and monolayer of self-assembled, silane based molecules was coated on hot embossed PVC film. UV nanoimprint process was done on the glass substrate using hot embossed PVC film. As a result, the transmittance of glass substrate was increased from 91 to 94% for single side patterned and 96% for both side patterned glass substrate for the spectral range of 350 to 800 nm.