Upconversion of 1.54 μm radiation in Er3+ doped fluoride-based materials for c-Si solar cell with improved efficiency
Laboratoire de Chimie de la Matière Condensée de Paris LCMCP UMR7574 CNRS/UPMC/Chimie ParisTech, Chimie ParisTech, 11 rue Pierre et marie Curie, 75235 Paris, France
2 Center for Information and Optics Technology, University of Information Technology, Mechanics and Optics, 199034, St. Petersburg, Russia
3 IRDEP, UMR 7174CNRS/EDF/Chimie ParisTech, 6 quai Watier, 78401 Chatou, France
Received: 3 January 2011
Accepted: 1 June 2011
Published online: 6 October 2011
Upconverted emission from erbium ions in fluoride materials (glass and disordered crystal of the system CaF2-YF3) are observed in a wide spectral range (from the visible to the near infrared) under infrared excitation at 1.54 μm. In both cases, the upconverted emission in the near infrared (~1 μm) dominates the spectrum. Absolute UC efficiency defined as the ratio between the UC luminescence power and the absorbed pump power has been experimentally measured. The NIR (~1 μm) luminescence energy yield for the glass and the disordered crystal varies from 2.4 to 11.5% for the glass and from 7.7 to 16% for the crystal for an infrared excitation power density ranging from 2 W/cm2 to 100 W/cm2. This is of a particular interest for their use as upconverter to improve the c-Si cells quantum efficiency since the energy of the excitation lies below the c-Si absorption edge (1.12 eV at 300 K) and is well located compared to the AM1.5G solar spectrum, outside of the absorption lines due to different atmospheric gases. Furthermore, the most efficient upconverted emission recorded in the investigated materials occurs at an energy just above the gap. A current generated in a bifacial c- Si solar cell is observed when the Er3+ doped material (1.55 mA and 2.15 mA for the glass and the crystal respectively), placed at the rear face of the cell, is excited at 1.54 μm. The current dependence as a function of the sub-bandgap excitation power has been measured and modelled. Finally the EQE of the complete device is deduced from the measured short-circuit current and the incident photon flux on the cell. An increase of the cell quantum efficiency of 2.4% and 1.7% is obtained at 1.54 μm with adding the glass and the crystal respectively at the rear face of the c-Si cell. The results are compared to those already obtained with Er: NaYF4 known as the most efficient upconverter.
© EDP Sciences 2011
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited.