1. Electrodeposition of CdSe photoabsorber thin films in the presence
of selected organic additives
S. Hamilakis n
, D. Balgis, K. Milonakou-Koufoudaki, C. Mitzithra, C. Kollia, Z. LoizosQ1
School of Chemical Engineering, National Technical University of Athens, 9, Iroon Polytechniou Street, Zografou Campus, Athens 15 780, Greece
a r t i c l e i n f o
Article history:
Received 28 November 2014
Accepted 14 January 2015
Keywords:
Solar energy materials
Cadmium selenide
Hybrid semiconductors
Organic additives
Choline chloride
Monosodium L-glutamate
a b s t r a c t
Photoabsorbing CdSe semiconductive thin films were prepared by cathodic electrodeposition onto
titanium substrates from an acidic aqueous electrolytic bath, containing some selected, commercially
available organic salts as additives, specifically monosodium L-glutamate and choline chloride. The
products obtained were fully characterized with XRD and SEM–EDAX techniques and their photoelec-
trochemical behavior was studied using a photoelectrochemical cell (PEC). It is observed that the use of
both additives leads to more uniform and in many cases to better crystallized deposits. All films, taken in
the presence of the additives, exhibit some differences in their semiconductive behavior, in comparison
to the pure CdSe ones. However, the addition of monosodium L-glutamate salt into the bath brought
about a clear improvement in photoresponse of the deposits, whereas the use of the choline chloride salt
clearly led to a deterioration of their photoconductivity. It is considered that the organic ions of the salts
(L-glutamate anion and choline cation) are potentially adsorbed on the CdSe deposits, thus introducing
crystal defects, which modify the electric properties of the final products.
& 2015 Published by Elsevier B.V.
1. Introduction
Cadmium chalcogenides, such as CdSe, CdTe and Cd(Se,Te)
alloys, are well-known semiconductive compounds presenting a
particular interest as they have found applications in the field of
photocatalysis and conversion of solar energy [1–5]. They belong
to the compounds formed between elements of 12th (zinc group)
and 16th (chalcogens: oxygen group) of the periodic table, e.g.
CdSe and CdTe. These example compounds possess direct energy
gaps (1.7 and 1.5 eV, respectively), which are more efficient to the
absorption of electromagnetic radiation. Moreover, using these
compounds, the exploitation of a large part of the photons present
in the solar spectrum can be attained.
Cathodic electrodeposition of Cd chalcogenides is extensively
investigated in [6,7], where the concept of potential preparation of
compact, polycrystalline, semiconductive compound films by under-
potential deposition (upd) of Cd, in a potentiostatic manner, was
described. The lattice structure of CdSe can be found in the forms of
zinc blende (cubic) and wurtzite (hexagonal). The former is a met-
astable phase, constituting the almost exclusive product of an
electrochemical formation process, while the latter is the thermo-
dynamically stable structure obtained either by annealing the cubic
phase or directly by various, electroless deposition techniques [2–4].
Photoelectrochemical research has a far-reaching interest in
cadmium chalcogenide semiconductors since they can be effec-
tively used as active electrodes in relatively stable photoelectro-
chemical cells (PEC) for solar energy conversion. Moreover,
polycrystalline anodes, particularly of CdSe, have signified the
potential advantages of the liquid–solid junction compared to
solid state ones [1–5,8,9].
In our previous work [10] we have investigated the role played
by some slightly water soluble fullerene derivatives, introduced in
the electrolytic bath during the electrodeposition of cadmium cha-
lcogenides. It was found that these chemical species can be co-
deposited with the inorganic ones, giving hybrid systems posses-
sing improved semiconductive behavior such as their photore-
sponse in PEC.
In the present work we attempted to continue and extend our
research using in the place of the fullerene salts some low cost and
commercially available organic compounds, such as monosodium
L-glutamate and choline chloride. These salts, readily soluble in the
water, provide in their aqueous solutions (working pH¼2.2) organic
species, specifically L-glutamate cations (glutamic acid isoelectric
point: pH¼3.2) and choline cations, respectively. Thus, their behavior
may differ during the electrodeposition process. Moreover, it is already
known that glutamic salts and their derivatives are used as surfactants
or additives in metal electroplating baths, modifying the grain size
of the deposits [11,12]. Organic additives often tend to favor the
development of most crystallites to some dominant textures, mostly
inhibiting crystal growth towards other crystallographic axes [13], so
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Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/matlet
Materials Letters
http://dx.doi.org/10.1016/j.matlet.2015.01.052
0167-577X/& 2015 Published by Elsevier B.V.
n
Corresponding author. Tel: þ30 210 772 3258; fax: þ30 210 772 3188.
E-mail address: hamil@chemeng.ntua.gr (S. Hamilakis).
Please cite this article as: Hamilakis S, et al. Electrodeposition of CdSe photoabsorber thin films in the presence of selected
organic additives. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.01.052i
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎

2. influencing the properties of the deposits. We may expect that the
above chemical species should function as additives, introducing
crystal defects, modifying thus the electric properties of the deposits.
2. Experimental
CdSe thin films were developed potentiostatically, using a
potentio-scan system with a conventional three electrode setup.
The cathode was a rotating Ti disc electrode (∅ 12 mm; cathode's
rotation rate: 500 rpm). The counter electrode was a large plati-
num plated grid. The potential of the working electrode was
monitored against an Hg/HgSO4 saturated sulfate reference elec-
trode (SSE). The electrolytic bath for CdSe plating was an aqueous
solution containing typically 0.2 mol/L CdSO4 and 2 Â 10À3
mol/L
SeO2 being kept constant at 8571 1C. The concentration of the
additives (monosodium L-glutamate or choline chloride) was set to
2 Â 10À3
mol/L. The bath pH was adjusted to 2.2.
All deposits were examined by X-Ray Diffraction (XRD; Siemens
D5000 using a Cu Kα X-ray source) and Scanning Electron Micro-
scopy (SEM; FΕΙ-Quanta 200) techniques. Compositional data were
obtained by Energy Dispersive X-ray (EDAX) analysis. Photoresponse
studies were performed in a photoelectrochemical cell (PEC) with a
three electrode configuration comprising platinum wire rods as
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Fig. 1. XRD diagram of CdSe thin films prepared by electrodeposition at À0.9, À1.0 and À1.1 V vs. SSE in the presence of monosodium L-glutamate (a) and choline chloride
(b) additives in comparison with the diagrams of pure CdSe.
Fig. 2. EDAX diagrams and SEM micrographs of CdSe thin films prepared by electrodeposition at À1.0 V vs. SSE in the presence of monosodium L-glutamate (before and after
surface etching) and choline chloride additives in comparison those of pure CdSe.
S. Hamilakis et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎2
Please cite this article as: Hamilakis S, et al. Electrodeposition of CdSe photoabsorber thin films in the presence of selected
organic additives. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.01.052i

3. counter and reference electrodes. An alkaline sulfide–polysulfide
solution (S2À
x 1 M NaOH, 1 M Na2S, 1 M S solution) was used as
the working redox electrolyte. The PEC measurements were con-
ducted under a white illumination generated by a halogen lamp and
focused in front of the quartz window of the cell. Illumination int-
ensity was 1000 W/m2
.
3. Results and discussion
Fig. 1 summarizes the XRD diagrams of the new semiconduc-
tive thin films prepared in the presence of monosodium L-glu-
tamate and choline chloride additives in comparison with the
diagrams of pure CdSe. It is found that all specimens exhibit a
well-developed cubic zinc blende structure with a predominating
crystalline orientation towards the [111] crystallographic axis, like
the electrodeposited pure CdSe [1–3].
An EDAX carbon peak (see Fig. 2) appears in all specimens,
prepared in the presence of the additives, as resulted from the
SEM–EDAX investigations, probably suggesting the development
of a hybrid system or, at least, the introduction of crystal defects,
which modify the electric properties of the final products.
Fig. 2 indicatively presents the EDAX diagrams and SEM micr-
ographs of CdSe thin films electrodeposited at À1.0 V vs. SSE in
the presence of glutamate (before and after surface etching) and
choline additives in comparison to those of pure CdSe. All the as-
prepared semiconductive thin films have good crystallized struc-
ture with nano-scaled grain sizes. Chemical species derived from
the additives are incorporated not only superficially but even in
the bulk of the deposit; indeed, EDAX carbon peaks still exists
after the surface etching, caused by the contact of the layer with
the corrosive sulfide–polysulfide solution during the PEC meas-
urements.
Table 1 summarizes the four parameters of the photoconversion
curves (short circuit current, jsc, open circuit potential, VOC, fill factor,
FF, and photoelectrochemical efficiency, η) for the CdSe thin films
prepared at À0.9, À1.0 and À1.1 V mV vs. SSE, in the presence of
monosodium L-glutamate and choline chloride additives, used
directly as absorbed electrodes in a conventional PEC. Fig. 3 illustrates
the current-potential photoresponses for the films electrodeposited
in the presence of the glutamate salt, which present the best solar
energy conversion efficiencies. For comparison, the corresponding
data of the pure CdSe, taken at the same conditions, are provided,
too. All photocurrents are anodic, that is characteristic of an n-type
behavior due to the variations of stoichiometry. It is also observed
that all deposits with the choline chloride additive have clearly
inferior properties such as short circuit current and photoelectro-
chemical efficiencies when compared with the reference specimens.
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Table 1
Photoelectrochemical parameters of CdSe thin films prepared by electrodeposition in the presence of monosodium L-glutamate and choline chloride additives.
Deposition potential (V/SSE) Pure CdSe CdSe/monosodium L-glutamate CdSe/choline chloride
À0.9 À1.0 À1.1 À0.9 À1.0 À1.1 À0.9 À1.0 À1.1
JSC (μΑ) 2128 2160 2701 3738 4207 4903 489 1018 296
VOC (mV) À412 À412 À367 À426 À393 À291 À184 À272 À277
FF 0.312 0.356 0.299 0.412 0.306 0.345 0.338 0.295 0.265
η (%) 0.274 0.317 0.296 0.656 0.507 0.492 0.030 0.082 0.022
Fig. 3. Current density vs. electrochemical potential given by CdSe thin films prepared by electrodeposition at À0.9, À1.0 and À1.1 V mV vs. SSE (curves a, b and c,
respectively) in the presence of Na L-glutamate additive (curves II) in comparison with the diagrams of pure CdSe (curves I), used directly as absorbed electrodes in a
conventional PEC in the dark and under illumination of 1000 W/m2
.
S. Hamilakis et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎ 3
Please cite this article as: Hamilakis S, et al. Electrodeposition of CdSe photoabsorber thin films in the presence of selected
organic additives. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.01.052i

4. On the contrary, all specimens deposited with the glutamate additive
have improved properties compared to the reference ones, displaying
approximately twice as many short circuits current and photo-
conversion efficiencies.
4. Conclusions
Two low cost and commercially available organic compounds,
specifically monosodium L-glutamate and choline chloride, have
been selected as additives during the electrodeposition of photo-
absorbing CdSe semiconductive thin films.
All the as-prepared thin films have a uniform and well-crys-
tallized structure with nano-scaled grain sizes, providing anodic
type currents, a typical behavior of n-type semiconductors.
Chemical species derived from the additives are incorporated in the
inorganic compound probably in the frame of an electro-codeposition
process, leading to a kind of a hybrid semiconductive system.
The thin films deposited with the choline chloride additive have
inferior semiconductive properties, as derived from the short circuit
current and photoelectrochemical efficiency values, when compared
with the reference specimens.
On the other hand, all the monosodium L-glutamate specimens
had improved and superior properties compared not only to the
reference ones but also with the products, obtained with other
electro-codeposition techniques [10], exhibiting the highest solar
energy conversion efficiencies.
It is considered that organic chemical species from the additives
can create crystal defects on the CdSe deposits, impacting positively
or negatively (in the cases of the glutamate and the choline chloride,
respectively) the photoconductivity of the final products.
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S. Hamilakis et al. / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎4
Please cite this article as: Hamilakis S, et al. Electrodeposition of CdSe photoabsorber thin films in the presence of selected
organic additives. Mater Lett (2015), http://dx.doi.org/10.1016/j.matlet.2015.01.052i