Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single j...Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single junction cell.This is beyond the efficiency limit implied by the Lambertian limit of ray trapping~29%.The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap.We compare two different methods for surface patterning,that can be extended to large area surface patterning:1)laser direct write and 2)step-&-repeat 5×reduction projection lithography.Large area throughput limitations of these methods are compared with the established elec-tron beam lithography(EBL)route,which is conventionally utilised but much slower than the presented methods.Spec-tral characterisation of the PhC light trapping is compared for samples fabricated by different methods.Reflectance of Si etched via laser patterned mask was~7%at visible wavelengths and was comparable with Si patterned via EBL made mask.The later pattern showed a stronger absorbance than the Lambertian limit6.展开更多
An explicit lighting estimation from a single image of Lambertian objects is influenced by two factors： data incompletion and noise contamination. Measurement of lighting consistency purely using the orthogonal spher...An explicit lighting estimation from a single image of Lambertian objects is influenced by two factors： data incompletion and noise contamination. Measurement of lighting consistency purely using the orthogonal spherical harmonic basis cannot achieve an accurate estimation. We present a novel signal-processing framework to represent the lighting field. We construct a redundant spherical harmonic frame with geometric symmetry on the sphere S2. Spherical harmonic frames are defined over the generating rotation matrices about symmetry axes of finite symmetry subgroups of SO（3）, and the generating functions are spherical harmonic basis functions. Compared with the orthogonal spherical harmonic basis, the redundant spherical harmonic frames not only describe the multidirectional lighting distribution intuitively, but also resist the noise theoretically. Subsequently, we analyze the relationship of the irradiance to the incoming radiance in terms of spherical harmonic frames, and reconstruct the lighting function filtered by the Lambertian BRDF （bidirectional reflectance distribution function）. The experiments show that the frame coefficients of spherical harmonic frames can better characterize the complex lighting environments finely and robustly.展开更多
基金project support by Nano-Processing Facility (NPF), AIST, Tsukuba, Japan where we were granted access to photo-lithography stepperARC DP190103284 "Photonic crystals: the key to breaking the silicon-solar cell efficiency barrier" project+1 种基金the visiting professor program at the Institute of Advanced Sciences at Yokohama National University (2018-20)Nanotechnology Ambassador fellowship at MCN (2012-19)
文摘Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single junction cell.This is beyond the efficiency limit implied by the Lambertian limit of ray trapping~29%.The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap.We compare two different methods for surface patterning,that can be extended to large area surface patterning:1)laser direct write and 2)step-&-repeat 5×reduction projection lithography.Large area throughput limitations of these methods are compared with the established elec-tron beam lithography(EBL)route,which is conventionally utilised but much slower than the presented methods.Spec-tral characterisation of the PhC light trapping is compared for samples fabricated by different methods.Reflectance of Si etched via laser patterned mask was~7%at visible wavelengths and was comparable with Si patterned via EBL made mask.The later pattern showed a stronger absorbance than the Lambertian limit6.
基金supported by the National Natural Science Foundation of China under Grant No. 60972126the Joint Funds of the National Natural Science Foundation of China under Grant No. U0935002/L05+1 种基金the Beijing Municipal Natural Science Foundation of China under Grant No. 4102060the Key Program of National Natural Science Foundation of China under Grant No. 61032007
文摘An explicit lighting estimation from a single image of Lambertian objects is influenced by two factors： data incompletion and noise contamination. Measurement of lighting consistency purely using the orthogonal spherical harmonic basis cannot achieve an accurate estimation. We present a novel signal-processing framework to represent the lighting field. We construct a redundant spherical harmonic frame with geometric symmetry on the sphere S2. Spherical harmonic frames are defined over the generating rotation matrices about symmetry axes of finite symmetry subgroups of SO（3）, and the generating functions are spherical harmonic basis functions. Compared with the orthogonal spherical harmonic basis, the redundant spherical harmonic frames not only describe the multidirectional lighting distribution intuitively, but also resist the noise theoretically. Subsequently, we analyze the relationship of the irradiance to the incoming radiance in terms of spherical harmonic frames, and reconstruct the lighting function filtered by the Lambertian BRDF （bidirectional reflectance distribution function）. The experiments show that the frame coefficients of spherical harmonic frames can better characterize the complex lighting environments finely and robustly.
