Upconversion mechanisms in rare-earth doped glasses to improve the efficiency of silicon solar cells

The electronic energy transfer properties between Ho3+ and Yb3+ ions have been studied in a fluoroindate glass for solar cell applications. The Ho3+ ions absorb infrared radiation at around 1150 nm, below the energy gap of Si solar cells. Energy transfer between Ho3+ and Yb3+ ions produces an upconversion emission in the visible and in the near infrared spectral range just above the Si bandgap. When these glasses are placed at the rear of a bifacial Si solar cell, the upconverted radiation can be absorbed by Si and generate electron-hole pairs that contribute to enhance the cell efficiency. An estimation of the expected increase in photo-current has been calculated when the upconverter material is used in a solar concentrator. Besides, they can be used alone or together with other Er3+ doped phosphors for the same purpose. The Ho3+-Yb3+ upconversion emission characteristics have been investigated as a function of the doping ion concentrations. Excitation, pump power dependency and dynamic experiments have been performed to determine the electronic energy transfer mechanism that is responsible of the upconversion. A rate equation analysis shows a reasonable agreement between the model and the experimental data. (C) 2011 Elsevier B.V. All rights reserved.