{"id":2763,"date":"2011-07-19T15:06:26","date_gmt":"2011-07-19T15:06:26","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/?p=2763"},"modified":"2011-07-19T15:06:26","modified_gmt":"2011-07-19T15:06:26","slug":"understanding-the-role-of-self-absorption-on-the-trapping-efficiency-of-luminescent-solar-concentrators","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/understanding-the-role-of-self-absorption-on-the-trapping-efficiency-of-luminescent-solar-concentrators\/","title":{"rendered":"Understanding the Role of Self-absorption on the Trapping Efficiency of Luminescent Solar Concentrators"},"content":{"rendered":"

Luminescent Solar Concentrators (LSCs) aim to reduce the cost of solar electricity by using an inexpensive collector to concentrate solar radiation without mechanical tracking (Figure 1a) [1<\/a>] <\/sup>. Ideally, the dyes re-emit the absorbed light into waveguide modes that are coupled to solar cells attached to the edges of the collector (black arrows). However, some photons are always lost, re-emitted through the face of the LSC, and coupled out of the waveguide (grey arrows). The trapping efficiency, \u03b7trap<\/sub><\/em>, is defined as the fraction of photons emitted from the edge versus photons emitted from the face and edge combined. Assuming the dyes emit their photons isotropically, \u03b7<\/em>trap<\/sub><\/em> is given by \u03b7<\/em>trap<\/sub><\/em> = [latex]\\sqrt{1-1\/n_5^2}[\/latex] . If the refractive index of the waveguide ns<\/sub> is ~ 1.7, then 20% of the re-emitted photons are lost.<\/p>\n

Such surface losses become compounded if photons trapped in the waveguide and travelling towards the edges are re-absorbed by other dye molecules in the waveguide; see Figure 1b. When such re-absorbed photons are re-emitted, the LSC will suffer more confinement losses, and the cycle repeats. As the number of re-absorption events increases, the overall efficiency of LSCs drops exponentially.<\/p>\n

In this work, we aim to quantify the contribution of self-absorption to the surface losses of an LSC. We vary the amount of self-absorption by tuning the dye concentration of ALq3<\/sub> and DCJTB in the waveguide (ns<\/sub> = 1.7). Figure 2 shows preliminary results for \u03b7<\/em>trap<\/sub><\/em> of an LSC with high and low self-absorption. The LSC with low self-absorption has \u03b7<\/em>trap<\/sub><\/em> of 78%, which approaches the theoretical \u03b7<\/em>trap<\/sub><\/em> of 81%. The slightly lower measured value of \u03b7<\/em>trap<\/sub><\/em> is likely to be explained by scattering losses from the LSC surface.<\/p>\n\n\t\t