Interdependence of reabsorption and internal energy losses in luminescent solar concentrators

Abstract

As a complementary device to photovoltaic (PV) cells, luminescent solar concentrators (LSCs) can reduce the cost of solar energy by replacing the expensive PV material with inexpensive energy-harvesting plastic or glass matrix. However, due to its low efficiency, LSCs are still not commercially viable. The low efficiency is due to the various losses associated with light harvesting and trapping. Most of these losses come from reabsorption and escape of reemitted energy from the LSC device. State-of-the-art LSC technology focuses on decreasing reabsorption loss by employing luminophores with a large Stokes shift. But these materials typically have low quantum yield. Increasing the Stokes shift of the luminophore reduces reabsorption but introduces substantial loss due to low quantum yield and the Stokes shift of the re-emitted photons. The interdependence of these losses is studied computationally using a ray-tracing model that accounts for reabsorption, Stokes shift, escape cone loss, and matrix loss. It is shown that using high Stokesshift luminophores does not give the highest energy efficiency. Higher energy efficiency is obtained by optimizing the Stokes shift. Even greater performance can be achieved by employing high-quantum-yield dyes with intermediate Stokes shift. LSC devices based on this approach could be nearly twice as efficient as those based on conventional luminophores, such as Rhodamine B.