Polymeric sheets suitable for use as solar concentrators in solar thermal devices are provided. Also provided are solar thermal devices incorporating the polymeric sheets. The polymeric sheets have two oppositely facing surfaces. A first pattern is defined in the first surface and a second pattern is defined in the second surface. The first pattern is designed to reduce the reflectance of light incident upon the first surface relative to the first surface in the absence of the first pattern and to channel incident light through the sheet onto the second surface. It does so by redirecting photons incident upon the first surface over a broad range of incident angles into transmittance angles that are more closely aligned with the surface normal of the polymeric sheet. The second pattern is designed to focus the photons transmitted to the second surface of the sheet onto a focal surface, such as a receptacle containing a heat-transfer medium.