Supplementary Material
Enhanced Mobility of Solution-Processed
Polycrystalline Zinc Tin Oxide Thin-Film
Transistors via Direct Incorporation of Water
into Precursor Solution
Genmao Huang, Lian Duan,* Yunlong Zhao, Guifang Dong, Deqiang Zhang, and Yong Qiu
Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education,
Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China.
The proposed chemical reactions with additional water are described as follows:
SnCl2 + H2O→Sn(OH)Cl+HCl
(1)
Sn(OH)Cl+Zn(OOCCH3)2+H2O→Cl-Sn-O-Zn-OH+CH3COOH(g)
(2)
→Zn2SnO3+MCl2(g)+HCl(g)+H2O(g)
Sn(OH)Cl+O2→SnO2+HCl(g)+H2O(g)
(3)
Considering the hydrolysis reaction in the precursor solution and wet film under low
temperature, SnCl2 would hydrolyze preferentially since the solution product constant (Ksp) of
Sn2+ is much smaller than Zn2+, as reaction (1) shows.
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Subsequently the intermediate Sn(OH)Cl could undergo different chemical reaction routes
depending on the amount of water. With adequate water, the self-condensation reaction between
Sn(OH)Cl and Zn(OOCCH3)2 would occur under moderate temperature, and it could facilitate
spinel Zn2SnO4 phase formation under high temperature. In the case of inadequate water
condition, Sn(OH)Cl preferred to form binary SnO2 under high temperature.
Therefore, reaction (2) and (3) are competitive reactions. It is the amount of water dominates
the chemical reaction route and phase transition. Besides, too much water in the precursor
solution (e.g. 2.50 M in this work) may have negative effect on the dehydroxylation process in
reaction (2), and results in less Zn2SnO3 formation.
FIG. S1. FT-IR spectra of ZTO films and a wet film.
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FIG. S2. Dielectric properties of the ALD-Al2O3 gate dielectric layer.
FIG. S3. Comparison of transfer characteristics between TFTs based on ZTO with Zn/Sn molar
ratio of 2:1 derived from precursor solutions without additional water and with 1.67 M water.
(a) Channel width/length=1400/20 μm. (b) Channel width/length=1400/30 μm.
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