She Mein Wong

Si nanopillar array optimization on Si thin films for solar energy harvesting

In this letter, Si thin film (800 nm thick) with nanopillar array decorated surface is studied via simulation for its solar energy absorption characteristics. It is found that the light absorption is significantly enhanced due to the adding of the Si nanopillar (SiNP) array to the Si thin film. The absorption characteristics of the SiNP structure would be approximately optimum (especially at ∼2.5u2002eV, the high energy density region in the solar spectrum) when the periodicity of SiNP array is set as ∼500u2002nm, which can be explained when comparing the incident light wavelength with the periodicity of SiNP array.

Design guidelines of periodic Si nanowire arrays for solar cell application

In this letter, optimum periodic Si nanowire (SiNW) arrays are designed via simulation for solar cell application, in terms of the structural parameters, e.g., the array periodicity (P) and SiNW diameter (D). It is found that the more efficient light absorption compared to that of the Si thin film with the same thickness could be realized when P is between 250 and 1200 nm. Further, the ratio of D to P should be >0.5 (or more specifically ∼0.8) for the optimized solar energy harvesting. The underlying physics is also discussed in this work.

Low aspect-ratio hemispherical nanopit surface texturing for enhancing light absorption in crystalline Si thin film-based solar cells

In this letter, we report light absorption enhancement in crystalline Si thin film-based solar cells through introducing low aspect-ratio hemispherical nanopit surface textures. Optical characteristics of the system are systematically investigated in terms of the structural parameters including nanopit diameter (D) and array periodicity (P) via simulation. An ultimate efficiency of ∼35.7% is predicted when both D and P are ∼700u2002nm, which is more than double of that (∼15.9%) of the flat Si film with the same thickness of 2u2002μm. An understanding on the light absorption enhancement is provided based on the optical processes in the subwavelength structures.

Si nanocone array optimization on crystalline Si thin films for solar energy harvesting

In this paper, the effects of structural parameters on the optical characteristics of crystalline Si thin films with the surface decorated by Si nanocone (SiNC) arrays are investigated by simulation. It is found that the SiNC base diameter should be equal to the array periodicity for efficient solar energy harvesting, and the optimized light absorption could already be realized when the SiNC height reaches ∼400nm. An ultimate efficiency of ∼31.5% can be achieved when the periodicity is ∼600nm for an 800nm thick Si film with a 400nm high nanocone array although the total thickness is only 1200nm. And the ultimate efficiency could be further increased to some extent due to the enhanced light absorption in the low energy region by appropriately increasing the Si film thickness. The underlying physics is also discussed in this work. (Some figures in this article are in colour only in the electronic version)

Boosting Short-Circuit Current With Rationally Designed Periodic Si Nanopillar Surface Texturing for Solar Cells

Large-scale rationally designed periodic Si nanopillar (SiNP) arrays of varying diameters and heights have been fabricated by a top-down method. The impacts of the structural parameters (e.g., diameter/periodicity/height) on the reflectance and absorption of the SiNP array have been extensively studied, and the results are in agreement with our theoretical prediction of Li et al. Owing to the notably enhanced light absorption of the optimized SiNP array, a short-circuit current density Jsc of 34.3 mA/cm2 was obtained on an axial p-n SiNP array surface-textured solar cell, which is the highest to date among reported Si nanowire/SiNP-based solar cells. Jsc is significantly boosted compared to that of the untextured solar cell (18.1 mA/cm2), which implies that the SiNP array is a promising texturing technology for thin-film photovoltaic application.

Surface nanostructure optimization for solar energy harvesting in Si thin film based solar cells

The solar energy harvesting of Si thin films with Si nanocone or nanopillar array decorated surfaces is systematically studied by simulation for the first time. It is found that the high and broad-width light absorption around 2.5 eV is the key to achieve high efficiencies for both structures. Nanostructure dimensions are optimized based on the enhanced light scattering, and thus the prolongated optical path around this energy. This work provides a practical guideline to design and fabricate Si thin film solar cells with high efficiency matching the bulk Si record.

Maskless fabrication of large scale Si nanohole array via laser annealed metal nanoparticles catalytic etching for photovoltaic application

In this paper, laser annealing is used to produce metal (Ag) nanoparticles as etching catalyst on a silicon surface, which enables controllable fabrication of large-scale nanohole array surface texturing without using a mask. Semispherical Ag nanoparticles with variable size and distribution are achievable by manipulating the laser annealing parameters and metal film thickness, and the underlying physics is clarified. The nanoholes array in silicon can then be realized by selective etching of silicon under Ag pattern. The optical characteristics suggest that the surface reflection can be significantly suppressed owing to the nanohole texturing, which is promising for thin film photovoltaic applications.

Boosting short circuit current with rationally designed periodic Si nanopillar surface texturing for thin film solar cell

This work experimentally investigates the impact of the large-scale rational-designed periodic Si nanopillar (SiNP) array structural parameters (e.g. diameter/ periodicity/ height) on the reflectance and hence the absorption of the SiNP array for the first time, and the results are in consistence with our theoretical prediction [1]. Owing to the significantly enhanced light absorption of the optimized SiNP array texturing, a short circuit current density (Jsc) of 34.3mA/cm2 is realized on planar p-n SiNP surface textured solar cell, which is the highest to date among reported Si nanowire (SiNW)/SiNP based solar cells. This is in distinct comparison to Jsc of 18.1 mA/cm2 demonstrated on the solar cell without SiNP, which makes the SiNP array a suitable and promising texturing technology for thin film photovoltaic application (alike the micrometer-scale surface texturing commonly used in Si wafer solar cell).

High-efficiency crystalline si thin film solar cells with Si nanopillar array textured surfaces

In this paper, high-efficiency crystalline Si thin film solar cells are reported via the incorporation of the Si nanopillar (SiNP) array textured surface. The power conversion efficiency of ∼18.1% is predicted for the cell configuration of the 1000 nm thick SiNP array (array periodicity: 500 nm; SiNP diameter: 250 nm) + 800 nm thick underlying Si film with the minority carrier diffusion length of ∼0.6 µm based on the optical and electrical calculations. This work points out the potential of the aforementioned cell structure in boosting the performance of Si thin film based solar cells while maintaining the low costs without using high grade raw materials. Except the device performance projection, the underlying physics responsible is also clarified.

A novel low aspect-ratio Si nano-hemisphere surface texturing scheme for ultrathin film solar cells

Low aspect-ratio Si nano-hemisphere array surface texturing compatible to ultrathin film solar cells is proposed and experimentally studied for both optical and electrical performance improvements. Light reflection can be significantly suppressed through rationally designed nano-hemisphere array surface texturing, thanks to the spatial effective refractive index (neff) modulation. Owing to the excellent light trapping and also to the nature of low aspect ratio (critical for conformal deposition of electrodes and achieving low surface defects), a record-high short circuit current density (Jsc) of 37.4 mA/cm2 among all published Si nano-structured solar cells is achieved, in distinct comparison with Jsc of 20.7mA/cm2 measured from the reference flat solar cells.