Elongated nanostructures for radial junction solar cells

Abstract

In solar cell technology, the current trend is to thin down the active absorber layer. The main advantage of a thinner absorber is primarily the reduced consumption of material and energy during production. For thin film silicon (Si) technology, thinning down the absorber layer is of particular interest since both the device throughput of vacuum deposition systems and the stability of the devices are significantly enhanced. These features lead to lower cost per installed watt peak for solar cells, provided that the (stabilized) efficiency is the same as for thicker devices. However, merely thinning down inevitably leads to a reduced light absorption. Therefore, advanced light trapping schemes are crucial to increase the light path length. The use of elongated nanostructures is a promising method for advanced light trapping. The enhanced optical performance originates from orthogonalization of the light's travel path with respect to the direction of carrier collection due to the radial junction, an improved anti-reflection effect thanks to the three-dimensional geometric configuration and the multiple scattering between individual nanostructures. These advantages potentially allow for high efficiency at a significantly reduced quantity and even at a reduced material quality, of the semiconductor material. In this article, several types of elongated nanostructures with the high potential to improve the device performance are reviewed. First, we briefly introduce the conventional solar cells with emphasis on thin film technology, following the most commonly used fabrication techniques for creating nanostructures with a high aspect ratio. Subsequently, several representative applications of elongated nanostructures, such as Si nanowires in realistic photovoltaic (PV) devices, are reviewed. Finally, the scientific challenges and an outlook for nanostructured PV devices are presented.

Spatial coherence of sunlight and its implications for light management in photovoltaics

“…where W s is the cross-spectral density in the device plane due to the uniform half-shell (explicit expressions for W ⊥ and W s are given in Appendix D). Equations (8) and 9are the main results of this section. They state that the cross-spectral density and spectral degree of coherence between two points in a device plane can be described by their relative distance (r), their orientation with respect to the Sun (θ 0 ; ϕ 0 ; ϑ), the transverse coherence functions of direct sunshine (W ⊥ , η ⊥ ), the frequency (ω), and the ratio (γ) between the spectral densities in the device plane due to the Sun and a uniform cloud cover or fog.…”

“…Multi-junction solar cells, which divide or selectively respond to portions of the solar spectrum, are the highest-efficiency cells ever produced [1]. However, spectral control is only a partial solution toward maximizing efficiency [2]; a complementary method for higher performance is the use of lightmanaging structures that capture or redirect light [3][4][5][6][7][8][9][10][11][12].…”

Boosting Visible Light Harvesting in p‐Type Ternary Oxides for Solar‐to‐Hydrogen Conversion Using Inverse Opal Structure

“…Furthermore, the doping approach possibly resulted in a CuO secondary phase within the absorber, leading to the formation of trap sites for photogenerated electrons. [17,18] However, these structures are usually investigated only for simple binary oxides such as TiO 2 , WO 3 , and SnO 2, [19][20][21][22] whereas the complex growth mechanism and limited phase stability of multinary materials hinder preferential growth on certain crystallographic facets. In this regard, several groups suggested the implementation of a ternary oxide nanostructure as a breakthrough solution to overcome these limitations.…”

“…[15,16] In general, 1D building blocks, such as nanowires, nanorods, and nanohelixes, are synthesized via epitaxial growth, seedoriented growth, and vapor-liquid-solid growth. [17,18] However, these structures are usually investigated only for simple binary oxides such as TiO 2 , WO 3 , and SnO 2, [19][20][21][22] whereas the complex growth mechanism and limited phase stability of multinary materials hinder preferential growth on certain crystallographic facets. Thus, several studies have been devoted to the nanostructuring of multinary materials using anodized aluminum oxide as a hard template.…”

Optical Response of Silver Nanoneedles on a Mirror

“…A free-standing metal nanowire within the solar cell is ideal as it combines the optimal light harvesting by scattering and efficient charge carrier extraction due to short electrical path length. Recent work on such structures in solar cells indeed provided increased efficiencies [ 25 , 26 ].…”