Black silicon photovoltaics

Abstract

The challenge of future solar cell technologies is the combination of highly efficient cell concepts and low cost fabrication processes. A promising concept for high efficiencies is the usage of nanostructured silicon, so-called black silicon. Due to its unique surface geometry the optical path of the incoming light through the silicon substrate is enhanced to nearly perfect light trapping. Combined with the semiconductor-insulator-semiconductor (SIS) solar cell concept it is possible to fabricate a low cost device by using conventional sputtering technologies. Therefore, a thin insulator is coated on the nanostructured silicon surface, followed by the deposition of a transparent conductive oxide (TCO), e.g. indium tin oxide (ITO) or aluminum doped zinc oxide (AZO). In such systems the TCO induces a heterojunction, hence, high temperature diffusion processes are not necessary. The optical and geometrical properties of different nanostructured silicon surfaces will be pr esented. Furthermore, the influence of the used TCO materials will be discussed and the solar cell performance under AM1.5G illumination of unstructured and structured SIS devices is shown

Black Silicon Photovoltaics

“…In this review article, we focus on the four most prominent fabrication methods of b-Si: dry reactive ion etching in an inductive coupled plasma (ICP-RIE), [ 15,46,51 ] electroless MACE with Ag [ 3,35,57 ] and Au [ 1,58 ] catalysts, photoelectrochemical anodization that leads to the formation of macP-Si, [ 12 ] and the irradiation of the surface with femtosecond (fs) laser pulses (L-Si) in vacuum. [ 39,40 ] The various black etching methods ( Figure 1 ) all lead to homogeneous macroscopically b-Si surfaces with a rather low refl ectance over the whole absorbing range of silicon as will be shown in section 1.8.…”

“…Hence, it is more desirable to optimize the black etching step to minimize initial surface damage and contaminations as proposed by Otto et al [ 46 ] Another idea for improving the blue response and avoiding DRE is to diffuse the emitter fi rst and to texture the front surface in a later step by a RIE-like technique. Füchsel et al [ 51 ] report on a b-Si solar cell using a semiconductor-insulator-semiconductor (SIS) concept REVIEW by sputter deposition of a transparent conducting ooxide (TCO) layer over a thin insulator covering the nanostructured surface. Nevertheless, by combining the phosphorus silicate glass (PSG) removal with the black etch, the number of process steps may be minimized that is desirable for industrial applications.…”

Black silicon: fabrication methods, properties and solar energy applications

“…214 The work function of the TCO layer leads to an inversion in the surface layer of the silicon substrate and forms a p-n junction. 236 Between the TCO layer and the silicon substrate, there is a layer of insulating oxide, typically made of SiO 2 or Al 2 O 3 (Fig. 37).…”

Black Silicon Photovoltaics

“…Another concept for a cost-effective fabrication of heterojunction solar cells on black silicon was presented by the authors [119,120]. In this case a sub-nm thin insulator and a layer of a transparent conductive oxide were coated onto black silicon fabricated by RIE-ICP to form a semiconductor-insulator-semiconductor (SIS) system.…”

“…In this case a sub-nm thin insulator and a layer of a transparent conductive oxide were coated onto black silicon fabricated by RIE-ICP to form a semiconductor-insulator-semiconductor (SIS) system. Owing to the poor quality and homogeneity of the thin insulator layer at the nanostructured surface, the open-circuit voltage was in the range of 427 mV and the efficiency was about 7.9% [120]. Owing to the poor quality and homogeneity of the thin insulator layer at the nanostructured surface, the open-circuit voltage was in the range of 427 mV and the efficiency was about 7.9% [120].…”