posted on 2021-06-04, 17:03authored byOlivier Fournier, Claire Darin Bapaume, Davina Messou, Muriel Bouttemy, Philip Schulz, François Ozanam, Laurent Lombez, Nathanaelle Schneider, Jean Rousset
We report on the modification of
zinc oxide thin films deposited
by atomic layer deposition (ALD-ZnO) with various phosphonic acid
derivatives. Particularly, three molecules differing by their spacer
and functionalizing groups were tested: 2-aminoethylphosphonic acid
(2-AEPA), 4-aminobenzylphosphonic acid, and 4-fluorobenzylphosphonic
acid (4-FBzPA). The resulting surfaces were investigated with surface-sensitive
characterization techniques such as X-ray photoelectron spectroscopy
and attenuated total reflection IR spectroscopy. We find differences
in the phosphonic acid film growth, mostly driven by the nature of
the functionalizing group: the amine-based molecules tend to cover
the surface with disordered layers or multilayers, whereas the 4-FBzPA
layer rather exhibits features of a monolayer. Finally, 2-AEPA and
4-FBzPA have been used as a mean to passivate the reactive interface
between ALD-ZnO and a hybrid organic inorganic metal halide perovskite.
Morphological and structural studies were carried out with scanning
electron microscopy and X-ray diffraction, and solar cells using these
layers as electron transport layers were synthesized. With the highest
power conversion efficiency of 4.1%, the direct application of these
surface modifications into complete devices is shown not to be enough
to achieve high-efficiency solar cells with ALD-ZnO.