Nanostructured crystalline silicon is promising for thin‐silicon photovoltaic devices because of reduced material usage and wafer quality constraint. This paper presents the optical and photovoltaic characteristics of silicon nanohole (SiNH) arrays fabricated using polystyrene nanosphere lithography and reactive‐ion etching (RIE) techniques for large‐area processes. A post‐RIE damage removal etching is subsequently introduced to mitigate the surface recombination issues and also suppress the surface reflection due to modifications in the nanohole sidewall profile, resulting in a 19% increase in the power conversion efficiency. We show that the damage removal etching treatment can effectively recover the carrier lifetime and dark current–voltage characteristics of SiNH solar cells to resemble the planar counterpart without RIE damages. Furthermore, the reflectance spectra exhibit broadband and omnidirectional anti‐reflective properties, where an AM1.5 G spectrum‐weighted reflectance achieves 4.7% for SiNH arrays. Finally, a three‐dimensional optical modeling has also been established to investigate the dimension and wafer thickness dependence of light absorption. We conclude that the SiNH arrays reveal great potential for efficient light harvesting in thin‐silicon photovoltaics with a 95% material reduction compared to a typical cell thickness of 200 µm. Copyright © 2012 John Wiley & Sons, Ltd.

The crossover from the semiclassical transport to quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the SdH theory could be due to the damping effects resulting from disorder and temperature. Moreover, we observed plateauplateau transition like behavior with such an extension. From our study, it is important to include the positive magnetoresistance to refine the SdH theory. Considerable efforts have been made to understand how Landau quantization affects the magneto-transport properties of two-dimensional electron systems (2DESs) under a perpendicular magnetic field B. It is well-known that Landau quantization can modulate the density of states and induce magneto-oscillations, which are periodic with respect to the inverse of B. The 2D Shubnikov-de Haas (SdH) theory, derived from a semiclassical approach, acts as the conventional tool to describe the low-field oscillations [1-5]. In practice, the analysis of low-field oscillations provides a common way to obtain three basic parameters of a 2DES, the carrier concentration, the quantum mobility, and the effective mass. In contrast, to explain the integer quantum Hall effect (IQHE) appearing at higher B, we shall consider quantum localization effects [1,6-9]. In the IQHE regime, there are a series of quantum Hall states characterized by quantized Hall plateaus and zero longitudinal resistivity. The magnetic-field-induced phase transitions in the IQHE provide good examples of continuous quantum phase transitions [10,11]. Universal properties based on the scaling theory and the modular symmetry have been investigated in the phase transitions in the IQHE [12-15]. While the universalities can be broken because of some unexpected factors, it has been shown that features of the scaling theory and modular symmetry can still be found after suitable analysis [16].It should be noted that the quantum localization effects are also important even as B approaches zero in the standard theory of the IQHE [7]. The low-field insulator induced by such effects has been observed in 2DESs with large disorder [17,18,19]. For a typical 2DES, in reality, the localization length becomes much larger than the realistic sample size with decreasing B [7,17]. In this way the semiclassical SdH theory, in which the localization effects are ignored, remains valid at low B for most 2DESs while quantum localization effects are still important to the appearance of the IQHE at high B [1]. Therefore, as the magnetic field B is increased, the crossovers from classical (semiclassical) transport to IQHE are expected in the low-field Landau quantization for a wide range of disorder.Although successful theories have been developed to understand the magneto-transport properties of 2DESs, there still exist many unresolved ...

In this work, effects of a hydrogen dilution ratio on the intrinsic amorphous hydrogenated silicon (i-a-Si:H) film of heterojunction silicon-based (HJS) solar cells were systematically studied. Long lifetime samples were obtained for R 5 5, indicating a good a-Si:H/c-Si interface. The dark conductivity was drastically decreased for R = 2, indicating a good film quality. Consequently, an optimized power conversion efficiency of the HJS solar cells was obtained at a moderate R between 2 and 5. In contrast to the previous emphasis on long lifetime, the results indicate that both the interface and film qualities are correlated to the hydrogen dilution, which are important to achieve high-efficiency HJS solar cells. We show that the most optimized HJS solar cell exhibits a marked efficiency of 17.27%.

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