Application of Cr
2
O
3
and
Mg
x
Cr
2−
x
O
3
as a Buffer Layer in Organic Solar Cells
Daragh Mullarkey
1
, Elisabetta Arca
1
, Linda Cattin
2
, Jean Christian Bernède
3
, Igor Shvets
1
1: School of Physics and CRANN, Trinity College Dublin, the University of Dublin, Ireland
2: Universitè de Nantes, Institut des Matériaux Jean Rouxel, France
3: Universitè de Nantes, MOLTECH-Anjou, France
E-mail
Organic solar cells show large improvements in efficiency when buffer layers are employed
between the organic layers and the electrodes. Some of the important effects these buffer
layers can provide are: increase the open circuit voltage of the cell, provide carrier selectivity
at the respective electrodes, and reduce reactivity between the organic layers and the
electrodes[1]. One class of materials which has the required properties to be an effective
buffer layer are transparent conducting materials [2,3].
Here, the use of the transparent conducting oxides, undoped Cr
2
O
3
and p-type
Mg
x
Cr
2−
x
O
3
[4]
as an anode buffer layer in a CuPc/C
60
organic solar cell is explored. The effects of the buffer
layer thickness, growth conditions and roughness on the properties of the solar cell were
studied. These effects were investigated for solar cells grown on both indium tin oxide and
fluorine doped tin oxide. In both cases, Cr
2
O
3
and
Mg
x
Cr
2−
x
O
3
buffer layers were found to
increase the open circuit voltage while also increasing the efficiency of the solar cell by a
factor of 2-3 when compared to a cell over the absence of a buffer layer. X-ray photoelectron
spectroscopy and Ultraviolet photoelectron spectroscopy were used to study the band offset
between the anode/buffer layer interface, and also the buffer layer/organic donor interface to
provide an insight into the origin of the improvement of the efficiency.
[1] R.
Po et al., Energy Environ. Sci
.
4,
285 (2011)
[2] V.
Shrotriya et al., Appl. Phys. Lett.
88
, 07350 (2006)
[3] A. Godoy et al., Sol. Energ. Mat. Sol. Cells.
94
, 648 (2010)
[4] L. Farrell et al., Phys. Rev. B
91
, 125202 (2015)
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