Electronic Supplementary Information
Enhanced photocathodic behaviors of Pb(Zr0.20Ti0.80)O3 films on Si
substrates for hydrogen production
Xiaorong Cheng, Wen Dong, Fengang Zheng, Liang Fang, and Mingrong Shen*
College of Physics, Optoelectronics and Energy, Collaborative Innovation Center of Suzhou Nano
Science and Technology, Photovoltaic Research Institute of Soochow University & Canadian
Solar Inc., and Jiangsu Key Laboratory of Thin Films, Soochow University, 1 Shizi street, Suzhou
215006, China. E-mail address: mrshen@suda.edu.cn
Experimental Section
Preparation of Si-pn+/ITO/PZT photocathode: We prepared pn+ junction from
multi-crystalline silicon (mc-Si) wafers (15.615.60.18 cm3, p-type, specific
resistance ρ=1-3 Ω.cm, GCL company, China) with a standard process of phosphorus
doping on a mass production line of mc-Si solar cells. The pit-shape texture of mc-Si
was achieved via a standard process of acid etching. First, the mc-Si wafers were
etched in HF/HNO3/H2O (HF in 70 g/L, HNO3 in 450 g /L) mixture solution at 10 0C
for 2 min. The wafers were then cleaned by deionized water (ρ=18 MΩ) for 25 s.
Second, the wafers were etched in KOH/H2O solution (KOH in 35 g/L, 20 0C) for 40
s. After cleaned by deionized water for 25 s, the wafers were dipped in a HF/HCl/H2O
(HF in 30 g/L, HCl in 40 g/L) mixture solution at room temperature for 30 s in order
to remove SiO2 on the surface and ions such as Pt2+, Au3+, Ag + and Cu2+. Finally, the
wafers were cleaned by deionized water and dried by hot air (50 0C) for 25 s.
Aluminum bottom electrodes were fabricated by a standard screen printing process.
The ITO layer (with a ratio of Sn:In=90:10) was deposited on the pn+ Si junction by
sputtering method (5 mTorr Ar pressure, 400 0C deposition temperature, 550 0C
annealing for 30 min under vacuum). Then a Pb(Zr0.20Ti0.80)O3 (PZT) film was also
deposited by sputtering (15 mTorr, O2:Ar =10:90 for 1 hour, 500 0C deposition
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temperature). After the deposition, PZT film was crystallized at 650 0C for 30 min in
air.
Sample characterizations: The PZT films were characterized by Rigaku D/MAX 3C
x-ray diffractometer using CuKα radiation. Scanning electron microscope surface and
cross-section images were checked by a Hitachi SU8010. For PEC measurements the
Si-pn+/ITO/PZT electrodes were cut into 1.51.5 cm2. Tinned copper wire was
connected to the aluminum bottom electrodes by gallium-indium eutectic
(Sigma-Aldrich). The exposed backside, edges, and some part of the front of the
electrodes were sealed with an industrial epoxy (PKM12C-1, Pattex). The
current-voltage curves of samples were measured by an electrochemical workstation
(CHI660D, CH Instrument) with a 100 mW cm-2 Xe lamp (Oriel, Newport Co.) as
light source and 0.1 M Na2SO4 solution as electrolyte. During the measurement,
Si-pn+/ITO/PZT served as working electrode, a Pt wire as the counter electrode and
an Ag/AgCl electrode as the reference electrode. The potentials were re-scaled to the
ones versus the reversible hydrogen electrode (RHE) according to the following
equation: E(RHE) = E(Ag/AgCl) + 0.197 V at pH = 0. Potentiostatic electrochemical
impedance spectroscopy was carried with an AC potential frequency range from 100
000 to 0.1 Hz. The incident photo-to-current conversion efficiency (IPCE) was
measured with a 100 mW cm-2 Xe lamp illumination in a 0.1 M Na2SO4 solution. The
IPCE value was calculated using the following equation: IPCE (%) = (1240I /
（Jlight）） 100%, where I is the photocurrent density (mA cm-2), Jlight is the power
density of the incident illumination (mW cm-2) and  is the incident light wavelength
(nm).
Poling the PZT film in Si-pn+/ITO/PZT: The poling of PZT films was carried out
using an electrochemical workstation (CHI660D) in 0.1M Na 2SO4 electrolyte. During the
poling, +10 V or -10 V pulsed voltage was added between ITO and the Pt reference
electrode.
The measurement of hydrogen evolution: The hydrogen and oxygen evolution by
PEC water splitting was conducted in the air-tight photo-reactor which was made of
quartz glass. In the photo-reactor, the photocathode and the counter Pt electrode were
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separated in different tubular chambers, which avoid the mixing of hydrogen
generated on the photocathode and oxygen on the Pt counter electrode. The
measurements were conducted in a solution containing 0.1 M Na2SO4 under 100 mW
cm-2 Xe lamp illumination. The amount of hydrogen was determined by a gas
chromatography equipped with TCD (Tianmei, GC 7890T).
Fig. S1 SEM images of Si-pn+ substrate fabricated by normal acid etching process.
Fig. S2 The optical reflectance spectra of planar Si wafer before (in black) and after acid etching
(in red).The reflectance of the Si-pn+ substrate after acid etching was less than that of the planar
Si wafer.
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Fig. S3 Polarization-electric field loop for the /ITO/PZT/Pt capacitor on Si-pn+ substrate. About
40 nm thick Pt top electrodes with diameters of 0.28 mm were sputtered onto the PZT film.
Hysteresis loops were then examined using a radiant precision ferroelectric analyzer from Radiant
Technology.
Fig. S4 The enlarged J-V curves for the Si-pn+ /ITO/PZT photoelectrodes with as-prepared (a)
and negatively (b) poled PZT films, respectively.
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Fig. S5 J-V curves for Si-pn+/ITO/TiO2 electrode with as-prepared (black), negatively (red) and
positively (blue) poled TiO2 films, respectively. The TiO2 layer was deposited on Si-pn+/ITO
substrate by sputtering method under 10 mTorr Ar pressure for 30 min and annealed at 400 0C for
2 hours in air. The thickness of TiO2 is also about 300 nm. Without the efficient
polarization-induced internal electric field the J-V curves show no obvious difference after
positively or negatively poling the TiO2 film. Only a small photocurrent (about -10 A cm-2 at 0 V
vs. RHE) can be observed in Si-pn+/ITO/TiO2 electrodes.
Fig. S6 J-V curves for Si-pn+ /ITO electrode, showing negligible photocurrent in the cathodic
region from 0 to -0.4V vs. RHE.
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Fig. S7 The SEM surface morphology of the Si-pn+/ITO/PZT photocathode with positively poled
PZT film before (a) and after (b) 3 hours continued PEC reaction. A Si-pn+/ITO/PZT sample was
cut into two pieces. One was taken to SEM analysis directly and the other was taken to SEM
analysis after 3 hours of continued PEC reaction. There is no obvious corrosion on the film
surface observed after the continued PEC reaction.
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