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Infra-red Photovoltaics: Redesigning Material And Architecture G.V. Shcherbatyuk, R. H. Inman, D. Medvedko, A. Gopinathan, R. Winston, and S. Ghosh University of California, Merced The performance of chemically synthesized lead sulfide (PbS) quantum dots (QDs) in non-tracking luminescent solar concentrators (LSCs) of planar, solid and hollow cylindrical geometries is evaluated using spectroscopic and photovoltaic techniques. Spatially resolved measurements are used to investigate and analyze the role of reduced self-absorption on the LSC efficiency. From comparative measurements of samples with Rhodamine B and CdSe/ZnS QDs it is established that PbS LSCs generate nearly twice the photocurrent in silicon cells than the other materials, achieving an integrated optical efficiency of 12.6% in planar geometry. Comparison between planar, solid and hollow cylindrical geometries shows the superiority of the hollow cylindrical geometry by virtue of lower self-absorption at the same amount of active material used. Abstract Introduction to LSCs Motivation Visible vs IR Luminescent Species Restructuring LSC Geometry – Planar To Cylinders Luminescent Solar Concentrators generally consist of a transparent polymer sheets doped with luminescent species. Incident photons are absorbed by the light emitting particles inside the concentrator. Particles then re-emit the light at longer wavelength, 70% of which is then trapped by total internal reflection. The emitted light is collected at the edges by standard Si PV cell. Idea largely abandoned due to dye stability PV CPV LSC Advantages of an LSC: • LSCs can concentrate both direct and diffuse light without tracking • They require less of the PV material which reduces the associated cost • They reduce heat dissipation problems • They are, in principle, easily integrable in building designs and existing architectural layouts. 12 8 0 2 4 4 Photo-exposure time (min) PbS Rhodamine B CdSe η opt (%) 0 100 125 time (min) 0.6 1.0 193 μM Summary of PbS QD-LSC measurements [1]: Higher un-optimized optical efficiency for PbS device Signal in solution decays with time PbS concentrator performs better even after hours of exposure to light Signal drop consists of reversible and irreversible parts Cylindrical LSCs (top) Encasing PbS QDs in a polymer matrix by radical polymerization stabilizes the output signal compared to when in solution. (bottom) PbS QD-PMMA composites forming solid and hollow cylindrical LSCs of varying QD concentration. 1 cm (a) Schematic of hollow cylindrical LSC. (b) Calculated absorption of normally incident radiation in hollow and solid cylinders plotted as a function of QD concentration for 3 different values of R 2 /R 1 . Solid squares are experimental data for R 2 /R 1 = 0.6. Surprisingly, the hollow modules absorb more incident light. Summary of cylindrical LSC measurements [2]: Theoretical calculation shows less self absorption for hollow cylinders when compared to solid modules and this is borne out by experimental data. Coupled with higher absorption, we find that the hollow cylindrical LSCs perform better than both planar and solid cylinders of similar geometric concentration factor. References: 1. Viability of Using Near Infra-red PbS Quantum Dots as Active Materials in Luminescent Solar Concentrators. Georgiy Shcherbatyuk, Richard Inman, Chunhua Wang, Roland Winston and Sayantani Ghosh, Appl. Phys. Lett. 96, 191901 (2010). 2. Cylindrical luminescent solar concentrators with near-infrared quantum dots. R. H. Inman, G. V. Shcherbatyuk, D. Medvedko, A. Gopinathan, and S. Ghosh, Optics Express 19, 24298 (2011).
