One of the factors limiting the efficiency of single-junction solar cells
to the Shockley–Queisser limit of ~31% is its intrinsic limitation on
absorbing photons with energy much higher than the band gap of the
active materials [1], losing the excess in thermal energy transferred to
the lattice. Down-converter (DC) materials are considered to be one of
the promising ways to overthrown this limit due to their capability to
turn one UV photon (which PV cells cannot use efficiently) into two
VIS photons [2–4]. Si-based solar cells and modules are very inefficient
absorbing the UV light and present low external quantum efficiency
(EQE) in this region mainly because (i) absorption and reflection losses
caused by the front glass, (ii) absorption in the encapsulation material,
(iii) parasitic absorptions and reflections due to the optimized λ/4
anti-reflective coatings at 600 nm, and (iv) high recombination rates
in the heavily doped emitter [5]. Therefore, DC processes can be used
to modify the solar spectrum to enhance the absorption spectrum of
the solar cells, increasing the external quantum efficiency (EQE) in the
UV spectral range.