Page 288 - A Comprehensive Guide to Solar Energy Systems

292 A COMPrehensIVe GUIDe TO sOlAr enerGy sysTeMs

13.3.2.1 Silicon and GaAs-Based Solar Cells
In 2012 Chin-lung et al. reported >2% increase in the conversion efficiency of a screen-
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printed monocrystalline silicon solar cells by using a layer of eu -doped y(Oh) 3 nano-
tubes [134]. In 2014 Chowdhury et al. reported an increase in J sc from 2.33% to 5.16% due
to the presence of si nPs deposited onto a asi:h (n+)/a-si:h (i)/c-si (p) hIT solar cell layer
stack [129]. In another study, Gardelis and nassiopoulou reported an increase of up to
37.5% in conversion efficiency of a si-based solar cell using CuIns 2 /Zns core-shell quan-
tum dots on the active area [130]. They attributed this improvement to the combined ef-
fect of downconversion and the antireflecting property of the dots. In 2015 Merigeon et al.
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successfully used Pr –yb co-doped with ZBlA (family of glasses with a composition of
ZrF 4 -BaF 2 -laF 3 -AlF 3 -naF) as downconverters on top of a commercial silicon solar cell
[135]. In 2016 Meng-lin Tsai et al. reported an increase in the efficiency of an n-type si
heterojunction solar cell using graphene quantum dots (GQDs) as downconverters [122].
In 2014 Chien-Chung et al. utilized a dual-layer of Cds QDs on a hybrid GaAs solar cell and
reported >2% increase in the overall power conversion efficiency [136]. In general, QDs
have been used as downconverters in GaAs-based solar cells. some examples are layers
of crystalline silicon nanopillar arrays and QDs of Cds and Zns nanoparticles/si nanotips
[123] and QDs of Cds and Cdse/Zns core-shell in colloidal solutions deposited on the top
layer of a GaAs cell [137].

13.3.2.2 Dye-Sensitized Solar Cells
In DssCs the downconverter can be integrated either with the photoelectrode and the dye
inside the cell or an additional layer containing the downconverter can be placed in the
front of the photoanode. One advantage of using an external layer is that, on the one hand,
it allows using energy in the UV range owing to its conversion to visible light and on the
other hand to improve stability on DssCs because it prevents degradation of the dye or
electrolyte caused by UV energy.
recently lanthanide ions as eu , sm [103], liGdF 4 :eu [138], Ca 3 la 3(1−x) eu 3x (BO 3 ) 5
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[139], among others on TiO 2 films have been studied as photoanodes. The DssCs were
reported to have increased efficiencies in all cases. A successful example is a solar cell
with a photoanode of TiO 2 doped with y 3 Al 5 O 12 :Ce proposed by Guang Zhu et al. with an
efficiency of 7.91% which is higher than an efficiency of 6.97% of a solar cell without the
downconversion layer [140]. Other typical oxides utilized in DssCs such as siO 2 , ZnO, sr-
TiO 3 , and nb 2 O 5 doped with phosphors for a downconversion approach were explored
lately [141]. In 2014 lim et al. [142] studied the possibility of using downconversion and
upconversion materials (double composite layer) on TiO 2 . The downconversion material
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was y 3 Al 5 O 12 :Ce while the upconversion material was Gd 2 O 3 :er /yb . These DssCs were
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reported to have about 21% higher PCe than the solar cell without the inclusion of the
double composite layer. recently, Chander et al. demonstrated that by using a nanophos-
phor yVO 4 :eu on a TiO 2 photoanode, it is possible to improve the absorption and out-
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door stability of a DssCs [143].