Study of Tb3+-Yb3+ doped Silicon Nitride frequency conversion layers for Solar Cell Applications

International audienceManagement of the solar spectrum is one of the key issues to improve the solar cell efficiency. Among the existing solutions, one consists in a layer absorbing energetic UV photons and converting them into two IR photons that match the absorption band of classical Si solar cells. This mechanism called frequency- or down- conversion process may increase the cell efficiency by almost doubling the number of IR photons absorbed as well as reducing the thermalisation losses. In this paper, we propose an innovative approach using a co-doped SiN matrix that presents the advantages of being compatible with Si solar cells fabrication process. Layers were deposited on Si substrates by reactive magnetron co-sputtering of Si, Tb, and Yb targets under a nitrogen-rich plasma. The microstructure of the grown layers were investigated using TEM, EDX and Glow Discharge Mass Spectroscopy while their optical properties and excitation mechanisms were analysed by means of ellipsometry, photoluminescence, and photoluminescence excitation spectroscopies. The quantum efficiency of the system has been studied through time-resolved photoluminescence experiments. Finally, optimized layers have been deposited on a solar cell to measure the carrier lifetime as well as the external quantum efficiency under AMG 1.5 illumination