Atomic Layer Deposition of Doped Zinc Oxide for Transparent Conducting
Layers in Solar Cells
L.P. Ryan
1
, A. Walsh
1
, M. McCarthy
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
Inorganic halide based perovskite solar cells have recently attracted significant attention due to their
excellent absorption properties across the visible and infrared electromagnetic spectrum, close to ideal
band gap and resultant power conversion efficiencies. However, they are not without problems, issues
with reliability, lead content and difficulties in scale up still require significant effort. In this paper we
focus on optimization of the TCO layers where low temperature (< 200°C) is required to prevent
damage to the under laying active layer. Using atomic layer deposition (ALD) we have studied zinc
oxide at various thicknesses (60-200nm).
In this study, diethylzinc (DEZ) was used to produce zinc oxide films by ALD at 200
o
C using a
Picosun ALD reactor. The number of cycles used to grow the films was varied from 200-1000 cycles
in order to vary the thickness of the films. Trimethylaluminium (TMA) was employed as the dopant
precursor (1-5 at %) using an ALD super cycle to generate nano-laminate type doping profiles.
Characterisation of the films deposited for greater than 200 cycles revealed polycrystalline XRD
features with sheet resistance values inversely proportional to film thickness. The average resistivity
values of ZnO films were all in the order of 10
-3
Ωcm, with the most conductive sample to date being
an Al-doped ZnO sample having a resistivity of 1.77 x10
-3
Ωcm.
The material properties are discussed with respect to their suitability in solar cells as compared to
traditional fluorine-doped tin oxide (FTO) based structures.
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