Solar photovoltaic (PV) technology is continuously increasing conversion efficiencywhile reducing cost. It has been sufficiently successful that by the end of 2013, installed capacity worldwide had reached 134GW,1 with 90% of market share made up of technology based on crystalline silicon (c-Si) wafers installed on rooftops (up to several kilowatts) or fields (tens to hundreds of megawatts). Despite this, PV still has a long way to go to reach multiterawatt capacity and play a significant role in our future electricity supply. Many alternative technologies are under development that will compete with standard c-Si technology, such as inorganic thin films, but also systems that concentrate light to a high (1000 times) or low (up to 10 times) extent. One such development is luminescent solar concentrators (LSCs), which are low concentration and relatively low cost, and they can also be shaped and colored. As a consequence, they are suitable for use as building facade elements with aesthetically appealing surfaces of variable shape and color. LSCs began to be developed in the 1970s as an alternative approach for reducing PV technology costs.2, 3 In LSCs, both direct and diffuse light is concentrated by a factor of 5–10. LSCs typically consist of a plastic plate, in which luminescent species are dispersed. These species absorb incident light and emit light at a wavelength that is a red-shifted with respect to the absorbed wavelength, as a result of the Stokes’ shift of the particular luminescent species. The majority of the emission (some is lost) is guided by total internal reflection to a solar cell at the side (see Figure 1).4 Ideally, an LSC should fulfill six requirements.5, 6 First, it should absorb all photons with wavelength >950 nm and emit them red-shifted at 1000nm for use with c-Si solar cells. Second, it should have minimal spectral overlap between absorption and emission spectra to keep re-absorption losses Figure 1. Schematic 3D view of a luminescent concentrator. AM1.5 light (mimicking the solar spectrum at temperate latitudes) is incident at the top. The light is absorbed by luminescent species, and its luminescence is randomly emitted. Part of the emission falls within the escape cone and is lost from the luminescent concentrator at the surfaces. Another part is guided to the solar cell by total internal reflection.4