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Luminescent down shifting (LDS) is a viable way for improving the short‐wavelength response of many photovoltaic technologies, such as cadmium telluride, copper‐indium‐gallium‐(di)selenide and multi‐crystalline silicon solar cells. In this work, we compare the experimental performance of LDS layers fabricated with six organic dyes—both alone and in mixtures—and two polymers with the theoretical predictions obtained by three different approaches: ray‐tracing simulations and two novel theoretical models. The first model is an analytical description of the LDS process and can reproduce the external quantum efficiency of the solar cell with LDS. The second one is based on a collection of figures of merit that address a desired property of the LDS. The three methods show an excellent agreement with the experimental results in the predicted variation of the short‐circuit current (to within 0.5% in most cases) and help to understand the key factors that influence the performance of LDS, such as the optical coupling, surface roughness and scattering or edge losses. This agreement, regardless of the materials used for LDS and the underlying PV technology, not only supports the validity of the models but also suggests this theoretical formalism as a tool for designing optimised LDS layers in the future. Copyright © 2014 John Wiley & Sons, Ltd.

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Luminescent solar concentrators (LSC) are a promising technology for building integrated photovoltaics (BIPV) given the wide variety of forms and colours that can be realised. Given the flexibility of the technology, the use of ray-trace modelling is indispensable in the design, performance evaluation, and optimisation of LSCs. This work begins by comparing a threedimensional (3D) ray-trace model of an LSC with experimental results. The study includes 70 samplesboth square and circular LSCs, containing five different fluorescent organic dyes (BASF Lumogen) each at seven different concentrations. The figure-of-merit used for performance evaluation was the average power density determined at the LSC edge sheet, measured using an optical fibre connected to a spectrometer. The results demonstrate that 3D ray-trace results gives good agreement with the experimental measurements, to within around ±5% within a wide concentration range (optical density = 0.05-8) and a maximum difference of ±13%. The wide range of colours achieved is presented in a CIE chart. Overall, the validated experimental results give confidence in the use of modelling for future larger LSCs for BIPV. Therefore, based on these results and the colours achievable, a model of a stained-glass window is constructed and its performance throughout a solar day is simulated.