Enhancement of Copper Indium Gallium Selenide Solar Cells Using Europium Complex as Photon Downshifter

This work reports on the use of a ternary europium (III) complex as down-shifting (DS) material for copper indium gallium selenide (CIGS) solar cells, [Eu(tta) 3(tppo) 2] (tta = 2-thenoyltrifluoroacetonate and tppo = triphenylphosphine oxide). It is synthesized by one-pot reaction and embedded into poly(ethylene-co-vinyl acetate) (EVA), poly(methyl methacrylate) (PMMA), and poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB) matrices. Their photophysical properties are investigated and compared with the complex alone. No significant variations in transmittance, emission, excitation spectra, and quantum yield are detected between [Eu(tta) 3(tppo) 2] alone and embedded into EVA, PMMA, and PVB. CIGS solar cells are encapsulated using these compounds, leading to an improvement of the external quantum efficiency (EQE) mostly in UV region. The EQE at 360 nm increases up to 56% compared to 14% without the encapsulant. The luminescent down-shifting (LDS) material is responsible for an increase in the short-circuit current (Jsc) calculated from the EQE in the 300-420 nm region, by 0.55 mA cm(-2) compared to the value of 0.59 mA cm(-2) obtained from theoretical prediction. In the best case, an increase of the CIGS solar cell conversion efficiency by 0.8% absolute is observed thanks to the LDS material.