Advanced Light Trapping in Thin-film Silicon Solar Cells

Abstract

Photon management is one of the key issues for improving the performance of thin-film silicon solar cells. An important part of the photon management is light trapping that helps to confine photons inside the thin absorber layers. At present light trapping is accomplished by the employment of the refractive-index matching layers at the front side and the high-reflective layers at the back contact of the solar cells and scattering of light at randomly surface-textured interfaces. In this article key issues and potential of light management in thin-film silicon solar cells are addressed. Novel approaches for light trapping are presented such as i) surface textures based on periodic diffraction gratings and modulated surface morphologies for enhanced scattering and anti-reflection, ii) metal nano-particles introducing plasmonic scattering, and iii) one-dimensional photonic-crystal-like structures for back reflectors.

Thin Film Silicon Solar Cells

“…The diffused reflectance increases with the texture; the total reflectance, however, decreases. For nc-Si:H with an intrinsic layer thickness of 1 mm, a single-pass will give a short-circuit current density (J sc ) of B15 mA cm À2 whereas for a random texture it can go up to 35 mA cm À2 (Zeman, 2010). The phenomenon of decrease in J sc with large texture has been observed in earlier studies and was attributed to parasitic losses.…”

Crystalline thin‐foil silicon solar cells: where crystalline quality meets thin‐film processing

“…For instance, wet random or inverted pyramid formation can be adapted to yield small peak‐to‐peak features. The small size of the scattering features was even proved to be beneficial . Dry plasma‐based texturing is another very interesting candidate because it has, amongst others, the advantage of providing an optically satisfying texturing with only 1–3 µm of material removed .…”

“…In order to increase the trapping of the light even further, resonant effects might also be considered. In fact, because of the even more stringent thickness limitations of thin‐film solar cells, the thin‐film community has been relatively active in developing advanced light‐trapping solutions, usually relying on patterns at a scale of (or smaller than) the wavelength (~100 nm) . A fundamental difference, nonetheless, is that for thin‐film solar cells (and also for the rare case of extremely thin c‐Si foils ), the active material is in the same order of magnitude as the light wavelength.…”

Thin-Film Silicon PV Technology

“…The most important role of light trapping is to keep the physical thickness of the absorber layer as thin as possible and to maximize its effective optical thickness. The following techniques are used to trap photons inside the absorber layer [13] • in-coupling of incident photons at the front side,…”