1 Controlled Photocatalytic Deposition of CdS Nanoparticles on2 Poly(3-hexylthiophene) Nanofibers: A Versatile Approach To Obtain3 Organic/Inorganic Hybrid Semiconductor Assemblies4 A. Varga,†,‡ B. Endrodi,†,‡ V. Hornok,‡ C. Visy,‡ and C. Janaky*,†,‡

5†MTA-SZTE, Lendulet Photoelectrochemistry Research Group, Rerrich Square 1, Szeged, H-6720, Hungary

6‡Department of Physical Chemistry and Materials Science, University of Szeged, Reirrich Square 1, Szeged, H-6720, Hungary

7 ABSTRACT: To efficiently harness the possible synergies, stemming from8 the combination of organic conducting polymers and inorganic semi-9 conductors, sophisticated assembling methods are required to control the10 composition and morphology at the nanoscale. In this proof-of-concept11 study, we demonstrate the in situ photocatalytic deposition of CdS12 nanoparticles on poly(3-hexylthiophene) (P3HT) nanofibers, exploiting the13 semiconducting nature of this polymer. The formation of the hybrid14 assembly was monitored by UV−vis and Raman spectroscopy, Energy-15 dispersive X-ray microanalysis, and X-ray powder diffraction (XRD).16 Transmission electron microscopic studies and AFM images confirmed that17 both the particle size and the loading can be tuned by the deposition time.18 Photoelectrochemical studies revealed the facile transfer of photogenerated19 electrons from P3HT to CdS, as well as that of the holes from CdS to20 P3HT. It is believed that ensuring intimate contact between the21 components in these nanohybrids will open new avenues in various application schemes, e.g., solar energy conversion.

22 ■ INTRODUCTION

23 Nanostructured hybrid assemblies of conducting polymers24 (CPs) and inorganic semiconductors (SCs) are among the25 most widely studied functional materials these days.1 Solar26 energy conversion,2 charge storage,3 and electrochemical27 sensing4 are only selected examples where the complementary28 properties of the constituents can be harvested. The success of29 the hybridization, however, strongly depends on the control30 achieved over the composition and nanoscale morphology of31 the hybrid material: most importantly, the properties of the32 interface between the components. Ex situ methods (e.g.,33 mechanical mixing or solution blending) generally fail to34 provide simultaneous control over the morphology and the35 interfaces in the hybrid. In most of these cases, surfactants are36 employed to avoid extensive aggregation of the inorganic37 particles. Such coatings, however, may hamper electronic38 communication (i.e., charge transfer) between the two39 semiconducting components.40 Consequently, in situ methods, where one component is41 obtained in the presence of the other one, are favored. The in42 situ-generated component can be either the CP or the43 inorganic SC.5,6 In situ chemical and electrochemical polymer-44 ization have been widely employed to synthesize CPs on45 inorganic SC surfaces; however, the limited electrical46 conductivity of these materials often hampered controlled47 electropolymerization.6,7 Considering the photoactivity of48 inorganic SCs, it is not surprising that feasibility of different49 light-assisted synthetic methods was demonstrated in prior50 studies. For example photocatalytic8 and photoelectrochem-

51ical7,9 methods were employed to deposit CPs (such as52polypyrrole, polyaniline, and poly(3,4-ethylenedioxythio-53phene)) on inorganic SC nanostructures. As we summarized54in a recent review article,6 these methods elaborate on the55oxidation of the monomer molecules by the holes, photo-56generated in the inorganic SC upon photoexcitation. The such57created radical cations form a dimer, which can be oxidized58again, and thus the polymerization proceeds. As a result, thin59CP coverage is obtained on the SC surface.60On the other hand, much less is known about the in situ61formation of inorganic SCs on organic CPs. Both polypyrrole/62CdS10 and poly(3,4-ethylenedioxythiophene)/CdS11 hybrids63were obtained via cathodic electrodeposition, where the CdS64particles were obtained in the CP film. The size of the CdS65particles in both cases, however, were out of the regime where66quantum size effects can be witnessed. Cathodic electro-67deposition of Cu2O and SnO2 was also performed on68polyaniline12 and polypyrrole13 films, respectively.69Direct precedence of this work was the photocatalytic70deposition of different metal chalcogenides on the surface of71TiO2 nanoparticles. Titania-based composites, containing72PbSe,14 CdSe,15,16 CdS,17,18 PbS,19 and Sb2S3

20 have been73realized through this method. This approach relies on the74photoexcitation of TiO2, followed by the reduction of the75respective metal cation in the presence of elemental S or Se.

Received: September 16, 2015Revised: October 20, 2015

Article

pubs.acs.org/JPCC

© XXXX American Chemical Society A DOI: 10.1021/acs.jpcc.5b09029J. Phys. Chem. C XXXX, XXX, XXX−XXX

pubsdm_prod | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i10:44431 | 2.0 alpha 39) 2015/07/15 14:30:00 | PROD-JCAVA | rq_5366077 | 11/26/2015 05:12:39 | 8 | JCA-DEFAULT

76 Mechanistic investigations in prior studies proved that the77 atomic route (M2+ + 2e− →M; M + S →MS) is dominantly78 responsible for the compound formation.21 It has also been79 shown that the conduction band edge position of the80 photoexcited SC particle (TiO2 in these studies), together81 with the reduction potential of the metal cation determines the82 feasibility, as well as the rate of the photodeposition reaction83 (i.e., the larger the difference the faster the reaction).15

84 In this article, we demonstrate a simple and versatile method,85 exploiting the intrinsic semiconducting nature of CPs to86 photodeposit metal−chalcogenide nanoparticles on their sur-87 face under visible light irradiation. The photocatalytic behavior88 of CPs has already been demonstrated and utilized in organic89 synthesis,22 dye-degradation,23 as well as noble-metal deposi-90 tion.24,25 In the presented study we exploit the photoelectrons91 generated in P3HT nanofibers to reduce Cd2+ ions, in the92 presence of elemental S, thus CdS nanoparticles are formed

s1 93 (Scheme 1). Our choice on the P3HT/CdS as a model system94 was deliberate, because we wanted to demonstrate the95 feasibility of this approach on a composite, which may have96 practical significance. Composites of poly(3-alkylthiophenes)97 and metal−chalcogenides are considered as benchmark98 materials of organic/inorganic hybrid solar cells.26,27

99 One-dimensional nanostructures of CPs have attracted100 significant attention recently,28 because of their enhanced101 electronic properties compared to their bulk counterparts. For102 example, self-assembled highly crystalline nanofibers of P3HT103 showed a 6-fold improvement in the electrical conductivity,104 rooted in the enhanced charge carrier mobility.29,30 Such105 beneficial features were exploited even in hybrid configu-106 rations;31 for example, P3HT nanofibers were decorated with107 CdSe32 and CdS33 (via a sophisticated chemical grafting108 procedure) and showed promising performance in solar cell109 studies.

110 ■ EXPERIMENTAL METHODS

111 Materials. All chemicals used were of analytical grade. 3-112 Hexylthiophene (≥99%), lithium perchlorate (≥98%) and113 absolute ethanol were purchased from Sigma-Aldrich, L-114 ascorbic acid, cadmium nitrate tetrahydrate, and sulfur from

115Reanal, acetonitrile from Carlo Erba, and tetrahydrofuran,116chloroform, and anisole from VWR International. Water117content of both anisole and chloroform was kept below 50118ppm (monitored by coulometric Karl Fischer titration) by119storing it over 3A zeolites.120Preparation Methods. Poly(3-hexylthiophene) (P3HT)121was prepared by oxidative chemical polymerization. Chloro-122form-based solutions of 3-hexylthiophene monomer and FeCl3123were prepared and mixed at final reagent concentrations of 0.1124and 0.25 M, respectively. The continuously stirred reaction125mixture was kept in a closed vessel on ice bath for 6 h. The126formed polymer was filtered on a filter paper (12−15 μm pore127size) and washed repeatedly with absolute ethanol to remove128the traces of the oxidant. The final product was dried in air,129under an infrared lamp.130The whisker method was employed to form nanofibers from131the bulk polymer. As the first step, a larger molecular weight132fraction of P3HT was extracted with tetrahydrofuran (THF).133Subsequently, the polymer was redissolved in a 9:1 ratio134anisole/chloroform mixture to get a final polymer concen-135tration of 1.0 g dm−3. Finally, the solution was warmed up to 70136°C and then instantly cooled to room temperature on an ice137bath.138P3HT nanofiber network thin layers were formed by drop-139casting the P3HT solution on indium−tin-oxide (ITO)-140covered glass substrates. The P3HT loading was about 100141μg cm−2.142Synthesis of P3HT/CdS Hybrids. P3HT thin layers were143placed in a closed cell and immersed in an ethanol-based144solution, containing the precursors of the CdS synthesis145([Cd2+] = 1.38 × 10−2 mol dm−3, [S8] = 1.72 × 10−3 mol146dm−3) and ascorbic acid (c = 0.1 mol dm−3), as sacrificial hole147scavenger. The solution was degassed by bubbling N2 through148it for 30 min before the synthesis. Photocatalytic synthesis of149the P3HT/CdS hybrids was then implemented by using a Fiber150Lite A3000 type tungsten halogen lamp (150 W maximum151power output), operating in the visible range, between λ =152380−800 nm. After the illumination, the hybrids were carefully153washed with distilled water and absolute ethanol, to remove the154adsorbed precursors on the surface. Solution blending was also

Scheme 1. Illustration of the Photocatalytic Synthesis of P3HT/CdS

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155 employed to synthesize randomly distributed P3HT/CdS156 hybrid samples with the same composition, for comparative157 purposes.158 Physical Characterization. Ex situ UV−vis−NIR spectro-159 scopic measurements were carried out using an Agilent 8453160 UV−visible diode array spectrophotometer in the range of161 300−1100 nm. To follow the gradual formation of the hybrids,162 the spectrum of the P3HT thin layer was recorded before the163 synthesis and was later used as background.164 Raman spectroscopic studies were performed on a DXR165 Raman microscope using a green laser (λ = 532 nm), operating166 at 1 mW laser power.167 A P3HT solution was drop-cast on copper mesh grids168 covered by carbon film for transmission electron microscopic169 (TEM) investigations. Formation of the hybrids occurred in170 situ on the P3HT-coated grids, according to the above-171 described method. Note, however, that during longer synthesis172 times (i.e., over 30 min) the copper grid corroded through its173 reaction with sulfur present in the solution. A FEI Tecnai G2 20174 X-Twin type instrument, operating at an acceleration voltage of175 200 kV was used.176 XRD spectra were recorded between 2Θ = 3−60° at 2°177 min−1 scan rate by a Rigaku Miniflex II instrument, operating178 with a Cu Kα,1 radiation source (λ = 0.1541 nm).179 Electrochemical measurements were performed in a three-180 electrode cell. A platinum sheet was used as counter electrode,181 while an AgCl-coated Ag-wire (having a potential of E = −420

182mV, compared to the Fe3+/Fe2+ redox transformation in183ferrocene in acetonitrile), was used as reference electrode. For184the photovoltammetric measurements (sweep rate 5 mV s−1),185the hybrids were periodically illuminated (0.1 Hz) with the186above-mentioned light source. All the measurements were187performed by using a PGSTAT 302 (Autolab) potentiostat/188galvanostat.189Scanning electron microscopic (SEM) images were recorded190by a Hitachi S-4700 field emission scanning electron micro-191scope (coupled with a Rontec EDX detector), operating at an192acceleration voltage of 10 kV.193AFM images were recorded on a Nanoscope III type atomic194force microscope (Digital Instruments) in tapping mode.195Silicon cantilevers (Veeco Nanoprobe Tips RTESP model,196125 μm length, 300 kHz) were used. The scanning rate was 1197Hz.

198■ RESULTS AND DISCUSSION

199To monitor the deposition process, the P3HT/ITO electrode200was placed into a closed vessel containing stoichiometric201amounts of the CdS precursors (Cd2+ and S) dissolved in202ethanol, and UV−vis spectra were recorded after selected203 f1irradiation times (Figure 1a). The pattern of the curves is very204similar in each case, exhibiting a broad absorption related to the205π−π* transition of the reduced P3HT.29 A fine vibronic206structure is also visible (with absorption bands centered at 550207and 600 nm) which is a solid indication of the presence of the

Figure 1. (a) Absorbance spectra recorded during the P3HT/CdS composite formation. (b) Difference spectra from part a. The inset in part bshows the Tauc-plot derived from part b, for the sample obtained by 2 h photodeposition.

Figure 2. (a) Raman spectrum. (b) XRD diffractogram of the bare P3HT nanofibers and P3HT/CdS composite (2 h synthesis). (c) EDX spectrumof a P3HT/CdS composite (2 h synthesis).

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208 nanofibers.28,30 Careful comparison of the curves, however,209 reveals a continuous absorbance increase between 300 and 550210 nm. To visualize these changes directly, difference spectra were211 obtained by subtracting the spectrum of P3HT recorded before212 irradiation (Figure 1b). The gradually developing difference213 spectrum indicates the steady formation of CdS nanoparticles.214 The bandgap energy of the formed material was calculated215 using a Tauc-plot (Figure 1b), and the values were in the range

216of 2.5−3.0 eV. In accordance with the small but significant

217gradual redshift of the absorption maximum (Figure 1b), a

218monotonous decrease in the bandgap energy was observed

219(from 3.01 (after 15 min) to 2.51 (after 120 min)). These

220tendencies indicate that initially very small nanoparticles

221(quantum dots) are formed, which later grow with the222deposition time. After 120 min, however, the bandgap of CdS

Figure 3. TEM pictures of P3HT (a) and three P3HT/CdS hybrids after 5 min (b), 15 min (c), and 30 min photodeposition (d). Particle sizedistribution of the CdS particles for the samples shown in parts b and c.

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223 reached the value generally reported for the bulk material (2.5224 eV).34,35

225 The chemical identity of the formed P3HT/CdS hybrid was226 confirmed by X-ray diffraction (XRD), Raman-spectroscopy,227 and energy-dispersive X-ray microanalysis (EDX). On the EDX

f2 228 spectrum, both Cd and S peaks were observed (Figure 2c).229 Semiquantitative analysis estimates about 10 wt % CdS content230 in the hybrid obtained after 2 h. Figure 2a depicts the Raman231 spectra of a P3HT nanonet and a P3HT/CdS hybrid (2 h232 photodeposition). In the P3HT spectrum, the Cα−S−Cα′233 deformation at 684 cm−1, the symmetric CαCβ stretching234 (the most intense peak) at 1455 cm−1, together with the235 asymmetric Cα′Cβ′ stretching at 1518 cm−1 are characteristic236 for the reduced form of P3HT.36 As for the hybrid material, the237 most important alteration is the appearance of a new band at238 303 cm−1, which is distinctive for the Cd−S stretching in239 CdS.37 In the XRD patterns presented in Figure 2b, both240 P3HT- and CdS-related diffractions are present. Clearly, P3HT241 is completely crystalline: the most intensive sharp reflection at242 2Θ = 5.2° (100), together with the two smaller one ((200) and243 (300)), is attributed to the lamellar ordering of the polymer244 chains, facilitated by the overlap of the aromatic rings (π-245 stacking) and the zipper-type connection of the hexyl side246 chains. The appearance of CdS-related broad diffractions,247 superimposed to the P3HT peaks, in the hybrid assembly248 points toward the formation of a nanocrystalline material. The249 diffraction pattern is consistent with the cubic CdS structure

250(hawleyite), as confirmed by literature data (JCPDS no. J 10-2510454). The Scherrer equation was employed to determine the252average crystallite size of the CdS particles, and d = 5.9 nm was253obtained. The broadening of the Raman bands as well as the254shift of the polymer-related diffraction peaks (in the XRD255pattern) to smaller 2Θ values is an indication of the partial256oxidation of P3HT during the hybrid formation (see details257below, as well as in Scheme 1).29

258Development of the morphological features of the hybrid was259monitored by transmission electron microscopy (TEM) and260 f3atomic force microscopy (AFM). Figure 3a−d shows the TEM261images of the bare PH3T nanofiber network and three P3HT/262CdS hybrids, obtained within 5, 15, and 30 min, respectively.263We note here that in the preparation of these samples, the264polymer nanofibers were directly casted on the TEM grid, and265the CdS nanoparticles were in situ deposited. During longer266synthesis times (i.e., over 30 min) however, the copper grid267corroded through its reaction with elemental sulfur present in268the solution. Beyond the obvious appearance of the nanofibers,269both individual CdS nanoparticles (dark spots) and some of270their aggregates are seen in the case of the hybrids (Figure 3b−271d). As seen in the histograms (see Figure 3e), the average size272of the primary particles was 6.8, 9.3, and 9.6 nm, after 5, 15, and27330 min, respectively (in agreement with the slight decrease in274the bandgap, shown above). At this juncture, we emphasize275again that the histograms depict the size distribution of the276primary nanoparticles (because that is the factor dictating the

Figure 4. AFM images of P3HT (a), P3HT/CdS 30 min photodeposition (b), P3HT/CdS after 60 min photodeposition (c).

Figure 5. Comparison of the reduction potentials of different metal cations and the band positions of TiO2, CdS, and P3HT.

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277 optical properties), and not that of the aggregated ones, which278 are visible in Figure 3d. Another important lesson learned from279 TEM images was that the CdS nanoparticles are always280 attached to the P3HT nanofibers, and they never show up281 among them, separately. This observation suggests that the CdS282 nanoparticles are formed at the nanofiber/solution interface283 and not in the bulk solution.

f4 284 AFM images, shown in Figure 4, depict very similar trends to285 those derived from TEM analysis. Most importantly, the CdS286 nanoparticles never grow individually at the supporting287 electrode surface; in contrast, they are evenly distributed288 along the P3HT nanofibers. In addition, the number of289 aggregated particles increases with time, and after 60 min they290 constitute a significant portion.291 Considering all the above data together as a whole, we292 propose the following mechanism illustrated in Scheme 1.293 Upon visible light irradiation, electron−hole pairs (excitons)294 are formed in P3HT. Some of these excitons reach the solid/295 electrolyte interface (before they recombine), and the photo-296 electrons then reduce the Cd2+ ions adsorbed on the P3HT297 surface or present in the solution. Note that the CB edge (or298 LUMO level) of P3HT lies more negative than the reduction299 potential of Cd2+; therefore, this process is thermodynamically

f5 300 feasible (see band edge positions in Figure 5). Because of the301 presence of dissolved sulfur, however, the formation of CdS302 occurs on the surface, instead of depositing metallic Cd303 particles. Ascorbic acid acts as a sacrificial electron donor, thus304 boosting the rate of the photocatalytic reaction (by scavenging305 the photogenerated holes). At this juncture, we turn back to the306 continuous increase in the particle size with time. Once CdS307 nanoparticles are formed, further CdS deposition is favored on308 the nanoparticles surface, because the photogenerated electrons309 in P3HT are rapidly transferred to CdS (see Figure 5, and the

f6 310 later discussion on the photoelectrochemistry data in Figures 6f7 311 and 7).

312 To validate the proposed mechanism, a set of control313 experiments was performed via the systematic variation of the314 synthesis parameters: (i) without ascorbic acid, (ii) in the315 presence of O2, (iii) no S in the solution, (iv) no Cd2+ in the316 solution, (v) no light irradiation. As expected, a much slower317 formation of CdS was witnessed in the first two cases. In the318 first case, extensive recombination and the lack of facile319 oxidative conjugate reaction (e.g., ascorbate oxidation) are both

320responsible for the decreased reaction rate. When O2 is present,321there is competition between the photoreduction of dissolved322O2

38 and Cd2+, which clearly hampers CdS formation.323Formation of metallic Cd deposits was experienced in the324absence of sulfur; however, the amount of Cd nanoparticles was325considerably smaller than that of CdS. Finally, no reaction was326observed in the last two cases.327Photoelectrochemical methods were employed to study the328photoactivity of the components in the hybrid configuration.329Linear sweep voltammograms (together with stationary photo-330current data; see Figure 7) were recorded for the P3HT/CdS331hybrid, as well as its constituents separately in 0.1 M LiClO4/332acetonitrile (Figure 6). This voltammetry technique consists of333a slow scan of the potential while the film irradiation is334periodically interrupted. In this way, both the “dark” and the335light-induced (photo)response of the samples can be evaluated336in a single experiment. Note that the photovoltammograms are337scaled differently to highlight the features of each individual338curve, and the arrows indicate the type of the photocurrents. As339for the bare P3HT nanofibers, cathodic photocurrents can be340detected at negative potentials, related to the p-type behavior of341the polymer. This cathodic photocurrent flow is sustained by342the reduction of dissolved O2. On the other hand, in the case of343CdS the photocurrents are anodic in polarity, consistent with344its n-type semiconductor behavior. The photocurrents arise345mainly from the photooxidation of adsorbed water traces, or346acetonitrile molecules. Note that no hole-scavenger is added to347the solution (unlike when photoelectrochemical studies are348typically performed in Na2S containing media).349The photovoltammogram of the hybrid material qualitatively350shows the features of both of its components: while cathodic351photocurrents below E = 0.1 V proves the p-type photoactivity352of P3HT in the hybrid configuration, the n-type behavior with353anodic photocurrents at higher potentials is related to CdS.354This behavior was also confirmed by stationary photo-355electrochemical experiments, where the photocurrents were356registered at constant potentials (Figure 7). However, the357absolute values of these photocurrents during the photo-358voltammetric scans is very interesting; while the cathodic359photocurrents are five times higher in the hybrid, the anodic360photocurrents show a 15−20 fold improvement compared to361the bare materials. This striking effect can be interpreted by the362good electrical contact between the components in the hybrid363material. Upon photoexcitation under cathodic polarization,364CdS is able to receive photoelectrons from P3HT (the CB edge365alignment favors this transition), thus boosting cathodic366photocurrents by reducing the probability of recombination.367As for CdS, the photogenerated holes can oxidize P3HT368(which acts a hole-scavenger in this case); thus, much higher369photoanodic currents can be measured in the hybrid370configuration. The spectacular enhancement of the photo-371currents in our photoelectrochemical measurements proves that372there is a rapid and facile electron transport through the373P3HT/CdS interface.374We further studied the effect of our in situ procedure (and375the resultant nanoscale architecture) by comparing and376contrasting these data with those obtained for a randomly377blended P3HT/CdS sample (not shown here). Importantly,378almost no enhancement of the CdS-related anodic photo-379currents were detected in this case. Finally, we emphasize that380these charge transfer processes are exactly the same which381occur in a P3HT/CdS hybrid solar cell; therefore, this synthetic382tool may be useful in that application avenue.

Figure 6. Photovoltamograms of P3HT, CdS, and P3HT/CdS(immobilized on an ITO electrode) in 0.1 M LiClO4/acetonitrilesolution under visible light irradiation (λ > 380 nm) at 5 mV s−1 scanrate.

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383 ■ CONCLUSIONS

384 This study adds to the library of synthetic procedures to obtain

385 hybrid organic/inorganic semiconductor assemblies. Photo-

386 catalytic deposition of CdS nanoparticles was achieved for the

387 first time through exploiting the intrinsic semiconducting

388 nature of P3HT. By a set of carefully designed control

389 experiments, we proved that upon illumination, photogenerated

390 electrons in P3HT reduce Cd2+ ions, which then react with

391 sulfur dissolved in the solution, to form CdS on the P3HT

392 nanofiber surface. By simply controlling the photodeposition

393 time, both the amount and size (between 3 and 12 nm) of CdS

394 nanoparticles can be tuned. We note here that this approach is

395 very versatile (similar data were gathered in our laboratory for

396 P3HT/Sb2S3); its applicability is only limited by the

397 conduction band edge of the polymer and the reduction

398 potential of the metal cation. Comparing and contrasting the

399 presented method to conventional electrodeposition, one has

400 to consider that, without being illuminated, most conducting

401 polymers (including P3HT) have very limited electrical

402 conductivity in their reduced form. Consequently, direct

403 cathodic electrodeposition of metal−chalcogenides is hampered404 by the low conductivity of the polymer. Controlled photo-

405 catalytic deposition circumvents the above issues and also

406 allows the deposition of metal−chalcogenides on CPs

407 immobilized on insulating surfaces. Finally, we hope that the

408 intimate physical and electronic contact between the two

409 components (as diagnosed by photoelectrochemical measure-

410 ments) may enable practical application of these hybrids in411 energy conversion and storage.

412■ AUTHOR INFORMATION

413Corresponding Author414*E-mail: janaky@chem.u-szeged.hu. Fax: +36 62 546-482. Tel:415+36 62 546-393.

416Author Contributions417The manuscript was written through contributions of all418authors. All authors have given approval to the final version of419the manuscript.

420Notes421The authors declare no competing financial interest.

422■ ACKNOWLEDGMENTS

423This research was realized in the frames of TAMOP 4.2.4. A/2-42411-1-2012-0001 “National Excellence Program − Elaborating425and operating an inland student and researcher personal426support system”. The project was subsidized by the European427Union and cofinanced by the European Social Fund. The428authors thank two anonymous reviewers for their insightful429comments on an earlier version of this manuscript.

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Figure 7. Chronoamperometric photoelectrochemical measurements of a P3HT/CdS composite (2 h) at different potentials, recorded in 0.1 MLiClO4/acetonitrile solution under periodic (tperiod = 30 s) visible light irradiation (λ > 380 nm).

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The Journal of Physical Chemistry C Article

DOI: 10.1021/acs.jpcc.5b09029J. Phys. Chem. C XXXX, XXX, XXX−XXX

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