Er(3+)/Yb(3+) upconverters for InGaP solar cells under concentrated broadband illumination

Area of Science:

• Materials Science
• Photovoltaics
• Nanotechnology

Background:

• Solar cell efficiency is fundamentally limited by the Shockley-Queisser (SQ) limit, which arises from the inability to utilize all incident photon energies.
• Upconversion is a process that converts low-energy photons, normally unabsorbed by solar cells, into higher-energy photons that can be utilized.

Purpose of the Study:

• To investigate the effectiveness of lanthanide upconverters (ytterbium and erbium ions in Gd2O2S, Y2O3, and NaYF4 hosts) integrated with a semi-transparent InGaP solar cell.
• To demonstrate the potential of upconversion to enhance solar cell performance by utilizing sub-band gap photons.

Main Methods:

• Fabrication and integration of lanthanide-doped upconversion materials with an InGaP solar cell.
• Illumination of the combined system with sub-band gap light (890-1045 nm) at a power density of 2.7 kW m(-2).
• Measurement of photocurrent generated in the solar cell with and without upconverters, and analysis of excitation-emission time delays and intensity dependence.

Main Results:

• A distinct photocurrent was measured in the InGaP solar cell when coupled with upconverters, while no current was observed without them.
• Energy transfer upconversion was confirmed by observing a time delay between excitation and emission for all tested upconverter systems.
• Upconverters using NaYF4 and Y2O3 hosts showed a quadratic dependence on illumination intensity, while the Gd2O2S host exhibited a linear dependence at higher power densities due to saturation.

Conclusions:

• Lanthanide upconverters can successfully convert sub-band gap photons into higher-energy photons, generating a measurable photocurrent in InGaP solar cells.
• The host material significantly influences the upconversion process and its intensity dependence, with saturation effects observed in Gd2O2S at high illumination levels.
• This research highlights a viable strategy for improving solar cell efficiency by overcoming the limitations imposed by the Shockley-Queisser limit through upconversion technology.