Page 289 - A Comprehensive Guide to Solar Energy Systems

Chapter 13 • Upconversion and Downconversion Processes for Photovoltaics 293

13.3.2.3 Organic Solar Cells
As other solar cells, OPV cells also present the possibility to increase their efficiencies
and UV stability through downconversion. In 2014 li et al. utilized smPO 4 nanophos-
phor as downconverter in a hybrid solar cell of TiO 2 /P3hT bulk heterojunction and re-
3+
3+
ported 3% increase in PCe [144]. In 2015 liu et al., utilized nayF 4 :yb /er nanophos-
phors into the TiO 2 (cathode) and reported an increase in the short circuit current in a
PCDTBT:PC 71 BM heterojunction solar [145]. In another study, na et al. reported a bi-
3+
functional layer of eu -doped ZnO for downconversion purposes in a P3hT:PC 61 BM
bulk heterojunction solar cell. The bilayer also served as an electron transporting layer.
An increase in the short circuit current density by about 2% was reported [146]. In a
similar scheme, svrcek et al used silicon nanocrystals (si-nc) with PTB7:PC 71 BM bulk
heterojunction solar cells and reported up to 24% photocurrent enhancement un-
der concentrated sunlight. In this hybrid solar cell, the si-nc was incorporated into a
PeDOT:Pss thin film [147].
13.3.2.4 Perovskite Solar Cells
Downconversion has also been explored to improve both the UV photon harvesting and
UV stability of PsCs [148–151]. In 2016 hou et al. reported 29% enhancement in PCe by
3+
incorporating ZnGa 2 O 4 :eu into PsCs [148]. In 2017 Jin et al. introduced fluorescent car-
bon dots, which could effectively convert ultraviolet to blue light in the mesoporous TiO 2
(m-TiO 2 ) layer of the traditional PsCs and reported around 12% increase in the PCe. The
devices were reported to maintain nearly 70% of the initial efficiency after 12 h of full
sunlight illumination, while the bare devices maintain only 20% of the initial efficiency
[149]. In another study, Jian et al. used a transparent luminescent downconverting layer
of an eu-complex (eu–4,7-diphenyl-1,10-phenanthroline) in PsCs and reported an en-
hancement of 11.8% in short-circuit current density (J sc ) and 15.3% in PCe [150]. similarly,
Chen et al. reported enhanced photovoltaic performance (35% increase in PCe) and UV-
3+
stability of PsCs by applying downconversion CeO 2 :eu nanophosphor—TiO 2 composite
electrodes [151].

13.4 Conclusions
This chapter provided a comprehensive overview on photon conversion/spectral con-
version as a potential approach to address the transmission and thermalization losses
in PV devices ranging from conventional crystalline si and amorphous si solar cells to
the emerging technologies including organic solar cells, dye-sensitized solar cells, and
perovskite solar cells. Where as in the former the spectral conversion layers are integration
on the front and/or rear of the PV device, the emerging technologies give the extra pos-
sibility of integration within the device. To exploit the full potential of photon conversion/
spectral conversion concentrated research efforts toward optimizing the materials as well
as devices is important.