TECHNOLOGY FOCUS - ELECTRONICS - Preferred Device: The light directing feature is operable to cause incident light to propagate through a composite structure of the device in a waveguide mode, where the composite structure includes the substrate and the semiconductor layer. A thickness of the semiconductor layer is less than 2 mu m. The substantially transparent substrate is formed from a glass, glass ceramic, and polymer. The photovoltaic device further comprises a further thin-film semiconductor layer coupled to the second major surface of the substrate and includes a photo-sensitive p-n junction, where the light directing feature is operable to cause the incident light to propagate through the substrate and into the further semiconductor layer in a waveguide mode and to impinge upon the p-n junction many times. The photovoltaic device further comprises a light collecting device operable to direct solar light toward one of the side surfaces of the substrate so that the solar light is coupled into the substrate and into the semiconductor layer in the waveguide mode. The light collecting device is a solar concentrator having a focal axis directed toward the side surfaces of the substrate. It also has a convex edge characteristic of the side surfaces of the substrate. The photovoltaic device further comprises at least one light redirective element disposed proximate to at least one of the side surfaces of the substrate, where the light redirective element is operable to cause the light that has reflected many times between the first and second major surfaces of the semiconductor layer in the waveguide mode to the side surface to reverse and reflect a further many times between the first and second major surfaces of the semiconductor layer in a waveguide mode and to impinge upon the p-n junction a further times. The light redirective element is a prismatic structure, lens structure, reflector structure, scattering surface structure, or diffractive surface structure formed on the side surface. The photovoltaic device comprises: (a) a first substantially transparent substrate having first and second major surfaces and side surfaces; (b) a first thin-film semiconductor layer coupled to the first major surface of the first substrate and including a photo-sensitive p-n junction; (c) a second substantially transparent substrate having first and second major surfaces and side surfaces; and (d) a second thin-film semiconductor layer coupled to the first major surface of the second substrate and including a photo-sensitive p-n junction, where the first and second thin-film semiconductor layers are disposed facing one another in a spaced apart configuration forming a gap, and a light directing feature operable to cause incident light to propagate through the respective first and second substrates and into the respective first and second semiconductor layers in respective waveguide modes so that the light reflects many times between the first and second major surfaces and impinges upon the respective p-n junctions many times. The light directing feature is operable to cause incident light to propagate through a composite structure of the device in a waveguide mode, where the composite structure includes: (i) the first substrate and the first semiconductor layer; (ii) the second substrate and the second semiconductor layer; (iii) the gap and the first semiconductor layer; (iv) the gap and the second semiconductor layer; and/or (v) the gap and the first and second semiconductor layers. Preferably, the gap is 0.1-0.7 mm. The photovoltaic device further comprises a rod disposed in the gap between the respective first and second semiconductor layers, where the rod is operable to at least one of space the first and second semiconductor layers apart and focus at least some solar light into the gap so that the light propagates in the gap and into the respective semiconductor layers in waveguide modes impinging upon the respective p-n junctions many times. The photovoltaic device comprises: (a) a substantially transparent substrate having first and second major surfaces and side surfaces; and (b) a thin-film semiconductor layer having first and second major surfaces, coupled to the first major surface of the substrate, and including a photo-sensitive p-n junction; and (c) a light collecting device operable to direct solar light toward one of the side surfaces of the substrate so that the solar light is coupled into the substrate, through the substrate, and into the semiconductor layer in a waveguide mode so that the light reflects many times between the first and second major surfaces of the semiconductor layer and impinges upon the p-n junction many times. The rod includes further optical properties that cause the solar light to couple into one of the major surfaces of the substrate. The rod is formed from glass, transparent polymer, and/or plexiglass. The light collecting device includes a wedge-shaped rod having a longitudinal slot extending along a narrow edge; the substrate and thin-film semiconductor layer is located within the slot so that one of the side surfaces of the substrate abuts a bottom of the slot and the wedge-shaped rod includes optical properties that cause the solar light to be directed toward the side surfaces of the substrate and to direct light that would otherwise not couple into the substrate back toward the substrate and thin-film semiconductor layer. The wedge-shaped rod includes a convex domed surface opposite the slot defining a focal axis directed toward the side surfaces of the substrate. It also includes at least one side surface that extends from the narrow edge outward and angles away from the substrate and thin-film semiconductor layer toward an edge of the convex domed surface; and the side surface is operable to direct light that would otherwise not couple into the substrate back toward the substrate and thin-film semiconductor layer. The light collecting device further includes a reflector having a first edge located proximate to the substrate and thin-film semiconductor layer and angling away from it toward an opposite edge of the reflector and toward the solar concentrator, and the reflector is operable to direct light that would otherwise not couple into the substrate back toward the substrate and thin-film semiconductor layer. The light collecting device also includes an integrating-type hollow cylinder having a cylindrical wall defining an interior volume, where the substrate and thin-film semiconductor layer are located at least partially within the interior volume, and the cylindrical wall including a longitudinal slot extending along it defining an aperture for the solar light to enter the interior volume. The cylindrical wall also includes a reflective interior surface operable to direct the light at least one of: (i) toward one of the side surfaces of the substrate so that the solar light is coupled into the substrate and into the semiconductor layer in the waveguide mode; and (ii) back toward the substrate and thin-film semiconductor layer and to couple into one of the major surfaces of the substrate. The photovoltaic device comprises: (a) a substantially transparent substrate having first and second major surfaces and side surfaces; (b) a thin-film semiconductor layer coupled to the first major surface of the substrate and including at least one photo-sensitive p-n junction; and (c) a light collecting device including: (i) at least one solar concentrator having a focal axis operable to direct solar light toward one of the first and second major surfaces of the substrate, and (ii) at least one corresponding redirective element operable to direct the light entering the substrate through the one of the first and second major surfaces transversely with respect to the focal axis of the solar concentrator so that the solar light is coupled into the substrate and into the semiconductor layer in a waveguide mode, where respective dielectric constant discontinuities proximate to the first and second major surfaces of the semiconductor layer are operable to cause incident light to reflect many times between first and second major surfaces of the semiconductor layer in the waveguide mode and to impinge upon the p-n junction many times. The photovoltaic device further comprises an antireflection coating on the first major surface of the substrate between at least some of the thin-film semiconductor layers. The redirective element is reflective element or a prismatic element. The photovoltaic device comprises thin-film semiconductor layers, at least a first of the semiconductor layers coupled to the first major surface of the substrate and including first and second major surfaces, and each semiconductor layer including at least one photo-sensitive p-n junction. At least two of the thin-film semiconductor layers are stacked one atop the other.