Efficiency (>15%) for thin‐film epitaxial silicon solar cells on 70 cm² area offspec silicon substrate using porous silicon segmented mirrors

Abstract

We report on the beneficial use of embedded segmented porous silicon broad-band optical reflectors for thin-film epitaxial silicon solar cells. These reflectors are formed by gradual increase of the spatial period between the layer segments, allowing for an enhanced absorption of low energy photons in the epitaxial layer. By combining these reflectors with wellestablished solar cell processing by photolithography, a conversion efficiency of 15Á2% was reached on 73 cm 2 area, highly doped offspec multicrystalline silicon substrates. The corresponding photogenerated current densities (J sc ) were well above 31 mA/cm 2 for an active layer of only 20 mm.

Thin crystalline silicon solar cells based on epitaxial films grown at 165°C by RF-PECVD

“…Research on epitaxial growth for thin film crystalline silicon solar cells has gained in importance [1][2][3] due to the cost of crystalline silicon and lessons learned from this feedstock shortage.…”

The use of porous silicon layers in thin‐film silicon solar cells

“…This is due to the presence of various crystal grain orientations, surface roughness and variations in dopant concentrations. However, the resulting decrease in total reflection can be minimized and even avoided by using a linear or a ‘segmented’ type of chirped reflector 2, allowing a broader reflection bandwidth. In this concept the Bragg wavelength is designed not to be constant, but to intentionally vary within the porous stack.…”

Epitaxial growth of silicon and germanium on (100)-oriented crystalline substrates by RF PECVD at 175 °C

“…In most of these cases, except in reference [6], the substrate was kept at a relatively high temperature to favor the epitaxial growth (T 700 • C). These high temperature approaches have resulted in solar cell efficiencies of 17% for a 50 μm thick free-standing c-Si base material epitaxially grown on a porous Si substrate before being detached [10], or over 15% by growing a 20 μm thick epitaxial Si base on a seed substrate and also using diffusion processes [11], and about 7% when growing a 2 μm thick epitaxial layer by HWCVD at 700…”