Quantum dot solar concentrators: an investigation of various geometries

Abstract

A Quantum Dot Solar Concentrator (QDSC) is based on the Luminescent Solar Concentrator (LSC), a concept first introduced in the 1960s. LSCs consist of a flat plate of polymer material doped with a luminescent dye. A percentage of incident insolation, absorbed and re-emitted by the dye molecules is trapped inside the plate by total internal reflection. Reflective material situated on three of the edges and the back surface increases the trapping efficiency of the plate. Through successive reflection events light is concentrated onto a photovoltaic (PV) cell positioned on the fourth edge of the plate. Degradation of luminescent dyes prevented LSCs from being fully developed. A QDSC replaces luminescent dyes with semiconductor nanocrystals known as quantum dots (QDs). Passivation of QD cores with shells of higher band gap material is expected to provide increased stability. QDs offer further advantages such as broad absorption spectra to utilize more of the solar spectrum and size tunability that allows spectral matching of the QDs emission to the peak efficiency of PV cells. Small-scale QDSCs have been fabricated using QDs bought commercially. The QDs have an emission wavelength of 600nm, close to the peak efficiency of a typical silicon PV cell. The systems were electrically characterized using a 4 cm monocrystalline PV cell optically matched to the QDSC edge with silicon oil. To investigate the effect of shape and size on concentrator efficiency, four different sized quadratic, two triangular and three circular QDSCs of various diameters were fabricated.