Page 284 - A Comprehensive Guide to Solar Energy Systems

288 A COMPrehensIVe GUIDe TO sOlAr enerGy sysTeMs

with PCDTBT:PC 71 BM and P3hT:ICBA respectively as active materials and with 3.8% and
3.1% efficiencies under AM1.5G irradiation. An additional current due to upconversion
−2
of 0.048 mA cm was achieved at an equivalent concentration of 17.3 suns for the so-
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lar cell made of P3hT:ICBA. In another report a layer of β-nayF 4 :yb ,er nanoparticles
deposited on top of a glass/ITO/PeDOT:Pss/P3hT:PCBM/Ca/Al solar cell structure un-
−2
der irradiation with a 980 nm laser with 4.9 W cm was reported to achieve an eQe UC
2
−6
−1
of 0.004% (a normalized value of 8.9 × 10 cm W ) [88]. In 2017 lin et al. reported a
solid-state organic interband solar cell that shows enhanced photocurrent derived from
TTA that converts sub-bandgap light into charge carriers. Femtosecond resolution tran-
sient absorption spectroscopy and delayed fluorescence spectroscopy were used to pro-
vide evidence for the triplet sensitization and upconversion mechanisms, while exter-
nal quantum efficiency measurements in the presence of a broadband background light
were used to demonstrate that sub-bandgap performance enhancements achievable in
the device [89].
13.2.2.6 Perovskite Solar Cells
PsCs (e.g. based on Ch 3 nh 3 PbI 3 ) are usually unable to utilize light beyond the visible re-
gion limited by their intrinsic bandgap, which accounts for 58% of the total solar energy.
Consequently, upconversion has been recently explored as a promising way to harvest of
this region of the solar spectrum and transform it into available visible light to enhance
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the Ir response of PsCs. In 2016, Chen et al. integrated liyF 4 :yb ,er single crystal in
front of PsC and demonstrated efficiency enhancement [90]. In another study roh et al.
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introduced hydrothermally grown nayF 4 :yb ,er nanoprisms as upconverting centers
to the TiO 2 mesoporous layer in PsCs and showed an increase in PCe due to upconver-
sion [91]. later in 2017, Wang et al. demonstrated performance enhancement by using
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hydrothermally grown 3% er and 6% yb co-doped TiO 2 nanorod arrays as electron
transfer material in PsCs as compared to those based on undoped TiO 2 [92]. however,
in all these studies, the device characteristics under laser irradiation or under higher
solar concentrations (to clearly attribute the contributions as only due to upconveri-
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son) were not reported. In another study in 2016, he et al. incorporated nayF 4 :yb , er
upconversion nanoparticles as the mesoporous electrode for Ch 3 nh 3 PbI 3 based PsCs.
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3+
The incorporation of nayF 4 :yb , er nanoparticles as the mesoporous electrode led to
−2
a short-circuit current density of 0.74 mA cm upon excitation with 980 nm laser with
−2
28 W cm [93]. More recently in 2017, Zhou et al. demonstrated that semiconductor
plasmon-sensitized nanocomposites (mCu 2−x s@siO 2 @er 2 O 3 ), which could efficiently
convert broadband infrared light (800–1600 nm) to visible benefiting from the local-
ized surface Plasmon resonance (lsPr) of Cu 2−x s when mixed with TiO 2 paste and ap-
plied as electron extraction layer in a PsCs led to an expanded response in the range of
800–1000 nm. The short-circuit current density of the device was observed to increase
−2
with the power density of the 980 nm excitation laser with >0.85 mA cm obtained for
−2
45 W cm [94].