EuIII‐Based Nanolayers as Highly Efficient Downshifters for CIGS Solar Cells

Abstract

We report herein on the use of 13 ternary europium(III) complexes as downshifting (DS) material for copper indium gallium selenide (CIGS) solar cells. Their general formulae are [Eu(β‐Dik)3(NL)x] and [Eu(L)3], in which β‐Dik = 2‐thenoyltrifluoroacetonate, 4,4,4‐trifluoro‐1‐phenyl‐1,3‐butanedione and 4,4,4‐trifluoro‐1‐(2‐naphthyl)‐1,3‐butanedione and NL = diphenyl sulfoxide (x = 2), triphenylphosphine oxide (x = 2), bis[2‐(diphenylphosphino)phenyl] ether (x = 1), 5,6‐epoxy‐5,6‐dihydro‐1,10‐phenanthroline (x = 1) and 2‐(N,N‐diethylanilin‐4‐yl)‐4,6‐bis(3,5‐dimethylpyrazol‐1‐yl)‐1,3,5‐triazine (x = 1) and L = 4‐(4′‐tert‐butylbiphenyl‐4‐yl)‐2,2′‐bipyridine‐6‐carboxylate. Tris(β‐diketonate) ternary EuIII complexes are very good candidates for DS applications, and some of them have shown very promising results when embedded in a host organic polymer matrix typically used for solar cell encapsulations. Herein we report a new method for the direct deposition of luminescent nanolayer films on CIGS solar cells. Highly luminescent nano‐ and microlayer films with a thickness in the range of 150 nm to 10 µm have been obtained and characterized by optical microscopy, profilometry, spectrofluorimetry and external quantum efficiency (EQE) measurements. The efficient conversion of incident photons into red light was observed for films with a thickness of 400–600 nm, leading to a significant improvement in the EQE and short‐circuit current density (Jsc) in the UV region up to 0.81 mA/cm2. The absolute conversion efficiency increased by up to 0.8 %. The nanofilms, with the exception of those containing naphthyl derivatives, were found to be photostable and therefore represent a competitive alternative to doped polymer encapsulants.