ALD of various Transparent Electron Transport Layers (ETLs) for use in Planar
Perovskite Solar Cells
M. McCarthy
1
, A. Walsh
1
, S. O'Brien
1
, M.E. Pemble
1,2
, I.M. Povey
1*
1
Tyndall National Institute, University College Cork, Lee Maltings, Prospect Row,
Cork, Ireland
2
Department of Chemistry, University College Cork, Lee Maltings, Prospect Row,
Cork, Ireland
*corresponding author
In the last decade the study of organometallic perovskite solar cells has been
extensive with reported power conversion efficiencies reaching over 20%.[1-3] Despite these
favourable efficiencies at a low fabrication cost, long term stability remains an issue. In this
research various electron transport layers (ETL’s) for use in a planar perovskite solar cell
have been explored and optimised.
The typical ETL used in planar architectures to date has been pristine TiO
2
. Despite
this, the metal oxide has been shown to diminish stability of the solar cell over time due to its
restriction of charge transport. This can be associated with its misalignment of the conduction
band with the perovskite layer. Along with oxygen induced defects within the TiO
2
layer, this
leads to marked hysteresis in the solar cells current-voltage curve. Recent band gap
engineering studies have shown that SnO
2
has the potential of significantly diminishing such
hysteresis. This material has an improved alignment with the conduction band of the
perovskite and may also allow for enhanced electron extraction when compared to TiO
2
.[4]
Doping TiO
2
with Al
2
O
3
as an ETL has been reported to enhance the conductivity of the
material. The wide bandgap associated with Al
2
O
3
facilitates accelerated electron transport
through the perovskite layer.[5]
In this research the ETLs were grown using Atomic Layer Deposition (ALD) at
temperatures below 200°C which align with the prerequisites of silicon-perovskite
heterojunction cells.[6] SnO
2
thin films were grown using the precursor
tetrakis(dimethylamino)tin(IV) (TDMASn) at 185
o
C for 326 ALD cycles. Pristine TiO
2
and
doped TiO
2
were fabricated using a similar process using tetrakis(dimethylamino)titanium
(TDMAT) and trimethylaluminum (TMA) precursors. Thin films were deposited on FTO
coated glass substrates (Solaronix) using a Cambridge-Nanotech Fiji system. Thermal and
Plasma growth processes were utilized for the growth of these metal oxides and will be
described in detail. The difference in wettability and coverage of perovskite on these metal
oxides, along with efficiency of resulting solar cell, were analysed and compared to that of
TiO
2
.
1.
W.S. Yang
et al.,
Science
,
348
, 1234-1237 (2015).
2.
N.J. Jeon
et al., Nature
,
517
, 476- 480, (2015).
3.
S.D. Stranks et al.,
Science
342
, 341-344, (2013)
4.
J.P. Correa Baena,
Energy and Environment Science
, DOI:10.1039/c5ee02608c,
(2015)
5.
B. Roose et al.,
Chem. Soc. Rev
.,
44
, 8326-8349 (2015)
6.
J.P. Mailoa et al.,
Applied Physics Letters
,
106
, 121105 (2015)
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