TCMs for novel photovoltaic applications
M. Espindola-Rodriguez
1
, Valero G. Alfonso
2
, Y. Sánchez
1
, H. Xie
1
, M. Neuschitzer
1
, V.Izquierdo-Roca
1
,
Elena Mas-Marzá
2
, Francisco Fabregat-Santiago
2
, P. Pistor
1
, A. Pérez-Rodríguez
1,3
, E. Saucedo
1
,
and M. Placidi
1
1. Catalonia Institute for Energy Research, IREC. Jardins de les Dones de Negre 1, 08930 Sant Adrià de
Besòs (Barcelona), Spain.
2. Institute of Advanced Materials (INAM), Universitat Jaume I, 12006 Castelló (Spain)
3. IN
2
UB, Departament d’Electrònica, Universitat de Barcelona, C. Martí i Franquès 1, 08028
Barcelona, Spain
Several emerging photovoltaic applications are currently requiring the development and implementation
of transparent conductive materials (TCMs). This includes high band gap devices as top cells for
advanced tandem configurations and high efficiency bifacial solar cells for improved collection of
scattered light.
For tandem and bifacial solar cells, transparent conductive oxides (TCOs) are used as front and/or back
electrodes as high transmittance and low electrical resistivity are the necessary requisites for those
electrodes. In most organic materials, the direct hole-injection (extraction) from TCOs is inefficient
because of a significant energetic mismatch at this interface. Therefore, various transition metal oxides
(TMOs) layers are used in this work to circumvent this issue and provide a bridge between the different
materials’ transport levels. High band gap metal-organic halide perovskite solar cells with the
Glass/FTO/c-TiO
2
/m-TiO
2
/Perovskite/Spiro-OMeTAD/TMO/TCO structure were produced and
investigated in this work for top tandem solar cells applications. As perovskite and Spiro-OMeTAD are
temperature, solvent and moisture sensitive, a low temperature and dry processes are favored for the
deposition of the transport layer and transparent electrodes. In this work we demonstrate the use of
several TMOs like MoO
2
, MoO
3
and NiO as buffer layers deposited by thermal evaporation between the
Perovskite and TCO to enhance the hole-conductivity of the Spiro-OMeTAD layer. The optoelectronic
parameters of the perovskite-based solar cells are presented, demonstrating that the different TMOs under
investigation are stable against energetic particle bombardment emerging in plasma processes of TCO
deposition and can therefore act as a protective layer for the underlying organic materials used in tandem
configurations. The best results are achieved with MoO
3
that allows reaching efficiencies (Voc, Jsc) up to
8% (954mV, 17 mA/cm
2
).
Other advanced photovoltaic device are bifacial solar cells, those require also the use of TCOs as
substrates, to replace the conventional opaque Glass/Mo substrates in order to allow the transmittance of
some fraction of the electromagnetic spectrum. In this work two absorber materials (CZTSe and CZTSSe)
onto SnO
2
:F (FTO) and In
2
O
3
:SnO
2
(ITO) were investigated on bifacial solar cells with the
Glass/TCM/CZTSSe/CdS/ZnO/ITO structure. The results here presented evidenced the feasibility of
bifacial CZTSSe solar cells; for both absorbers the FTO substrate showed to be the best candidate with
front-efficiency (Voc, Jsc) values as high as 3.5% (23.5mA/cm
2
, 348.2mV). This implies the need of a
significant effort in the improvement of the back interface that is likely responsible for the decrease
observed in the device efficiency in relation to standard device architectures using Mo back contacts.
Several strategies under investigation are also presented; those include the insertion of a thin and semi-
transparent layer of Mo and optically transparent TMOs like MoO
2
, MoO
3
, TiO
2
to improve both the
ohmic contact and the band alignment at the back-contact/absorber interface.
In all these cases the perspectives on the combination of strategies including TCMs with efficient hole-
collection capabilities will be discussed for the development of complex transparent back contacts and
buffer layers structures with improved photovoltaic performance
.
PS2 14
-208-
