RESEARCH ARTICLE

Luminescent solar concentrators employing new Eu(TTA)3phen-containing parylene filmsMichele Tonezzer1,2,3*, Gianluigi Maggioni3,4, Antonio Campagnaro1,3, Sara Carturan3,4,Alberto Quaranta1,3, Monica della Pirriera2 and David Gutierrez Tauste2

1 Department of Materials Engineering and Industrial Technologies, University of Trento, Via Mesiano 77, 38050 Povo, Trento, Italy2 Leitat Technological Center, C/ de la Innovació 2, 08225, Terrassa (Barcelona), Spain3 Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Viale dell’Universita’ 2, 35020 Legnaro, Padua, Italy4 Department of Physics and Astronomy G. Galilei, University of Padua, Via Marzolo 8, 35131 Padua, Italy

ABSTRACT

New robust luminescent solar concentrators were produced by growing Eu(TTA)3phen-containing parylene thin films onpoly(methyl methacrylate) slabs through a novel co-deposition process. As it is the first time that Eu(TTA)3phen moleculeswere inserted in parylene matrix, the deposition process was investigated, and the features of the samples were extensivelyanalyzed. Fourier transform infrared spectroscopy analysis demonstrated the integrity of the vacuum-sublimated Eu(TTA)

3phen molecules. Atomic force microscope analysis showed the very flat surface of the films (Rq = 3.7 nm), which isstrategic in luminescent solar concentrators (LSCs) for minimizing the light scattering at the air/film interface. The opticalmeasurements demonstrated that Eu(TTA)3phen-containing parylene exhibits higher absorption than the conventional Eu(TTA)3phen films and the luminescence peaks characteristic of Eu(TTA)3phen compound. This indicates that the Eucomplex is not affected by the matrix interaction thus maintaining its extremely large Stokes shift. Moreover, the parylenematrix improves the luminescence intensity of the films: in fact, under the same absorption, these films show a lumines-cence intensity more than two times higher than standard Eu(TTA)3phen ones. The current–voltage (I–V) measurementsshow that, under the same quantity of Eu(TTA)3phen, Eu(TTA)3phen-containing parylene LSCs produce a current densitymore than twice as high as LSC without parylene and that their efficiency decreases more than ten times slower thanorganic-based LSCs at increasing illuminating area, thus highlighting the feasibility of developing large size LSCs.Copyright © 2014 John Wiley & Sons, Ltd.

KEYWORDS

luminescent solar concentrators; luminescence; thin solid films; europium; parylene

*Correspondence

Michele Tonezzer, Department of Materials Engineering and Industrial Technologies, University of Trento, Via Mesiano 77, 38050Povo, Trento, Italy.E-mail: Michele.Tonezzer@lnl.infn.it

Received 3 May 2013; Revised 21 January 2014; Accepted 2 May 2014

1. INTRODUCTION

Luminescent solar concentrators (LSCs) are based on lumi-nescent slabs: solar light incident on an LSC is absorbed bydyes, re-emitted into a guided mode in the slab, and finallycollected by photovoltaic (PV) cells mounted at the edge ofthe slab [1,2]. This way LSCs concentrate the light onsmall high-efficiency solar cells where geometric concen-tration is given by the ratio of the exposed surface to thearea of PV cells [3] LSCs present several advantages incomparison to the traditional optical solar concentratorssuch as: (i) LSCs accept both direct and diffuse light; (ii)are static and do not need voluminous and expensive solar

trackers; (iii) prevent the solar cells from overheating; and(iv) present a largely improved architectural integration.

Luminescent solar concentrators are generally com-posed by poly(methyl methacrylate) (PMMA) and polycar-bonate [4] polymer sheets in which luminescent dyes aredispersed. Recently, different geometries have been testedin order to improve the performances and the versatilityof LSCs: at this purpose, thin film devices obtained by cou-pling luminescent films with transparent waveguides havebeen proposed [5,6]. Despite the appealing concept, up tonow, two pressing drawbacks have slowed the introductionof LSCs as commercial devices: the self-absorption of thefluorescence and the limited photo-stability of the organic

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dyes. Several efforts have been performed to tackle thesedrawbacks, one of the main route consisting in usingnanorods [7,8]. In this work, new luminescent thin filmsbased on rare earth complex dispersed in a highly stablematrix have been developed as a new prospective in thefield of LSCs. For the first time, we inserted Eu(TTA)

3phen compound in a host polyxylilene matrix by meansof a novel physical vapor co-sublimation process. Thechemical structure of Eu(TTA)3phen is reported inFigure 1: it is composed by an organic part and Eu3+ ion,which are responsible for the absorption and the emissionprocesses, respectively. The energy transfer mechanismoccurring between organic ligands and central ion confersto this compound a large Stokes shift value, which resultsin zero self-absorption losses. Polyxylilene polymers,widely known as Parylene, were used as dye-hosting ma-trix owing to their transparency and barrier properties. Infact, thanks to the peculiar solvent-free deposition processbased on the vapor phase pyrolysis of paracyclophane [9],parylene can be deposited as uniform, conformal, andpin-hole free films providing an excellent barrier to bothliquids and gasses [10]. Owing to these outstanding prop-erties, parylene films have been used for improving the sta-bility of several typologies of devices such as organicdiodes [11], electronic boards and light-emitting diodes[12,13], and organic solar cells [14]. As the optical proper-ties of the common organic dyes are jeopardized by the si-multaneous effect of ultraviolet B (UVB) and oxygeninteraction, their dispersion into a hosting parylene matrixrepresents a promising solution for the development ofnovel luminescent materials. Nevertheless, in spite of theirpeculiar properties, parylene polymers have been rarelyused as dye-host matrices owing to the peculiar character-istics of their deposition process, which renders challeng-ing the coupling of a suitable process for incorporatingguest functional molecules. In this work, Eu(TTA)3phenmolecules are directly co-sublimated with parylene in thepolymerization chamber. This novel technique has recentlydemonstrated to strongly improve the robustness of dye-based LSCs without affecting their optical properties anddecreasing their performances [15]. After verifying the fea-sibility to sublimate Eu(TTA)3phen compound in a coarsevacuum, Eu(TTA)3phen-containing parylene samples with

different thicknesses were produced in order to study theinfluence of the thickness on the final performances ofthe LSCs. The physical features of the samples wereaccurately analyzed by atomic force microscopy (AFM),Fourier transform infrared spectroscopy (FT-IR), and opti-cal analyses. The performances of LSC devices were testedby coupling a silicon cell to one edge of the poly(methylmethacrylate) (PMMA) waveguide and measuring the cur-rent–voltage (I–V) curves under standard solar radiation(AM 1.5G). (I–V) measurements with different radiationarea were eventually analyzed for investigating the feasi-bility to develop large size LSC devices.

2. EXPERIMENTAL

2.1. Preparation of the samples

The molecular structures of parylene C and of the complextris(2-thenoyl trifluoroacetone) mono (1,10-phenantroline)europium (III) (Eu(TTA)3phen) are reported in Figure 1.Eu(TTA)3phen was synthesized according to a previouslyreported literature procedure [16] Di-chloro-di-p-xylylene(parylene C dimer) was provided from PPS (Germany) at>99% purity.

The apparatus used for the deposition of Eu(TTA)

3phen-containing parylene films is a Labcoater LC300(PPS) customized for the co-deposition of parylene mono-mer and Eu(TTA)3phen dye [17]. The deposition processeswere conducted at a pressure of 3 Pa using fixed amountsof parylene C dimer (2.5 g) and Eu(TTA)3phen powder(70mg). The films were grown on different substrates:lapped P-doped (100) silicon wafers (Bayville ChemicalCo.) for FT-IR, AFM and fluorescence measurements,400μm thick corning microsheet glass slides with arefractive index of 1.523 for optical absorption, and50 × 50 × 5mm3 PMMA slides for testing as LSC devices.

The substrates were placed on a rotating sample holderfor increasing the uniformity of the dye dispersion. The de-position rate and film thickness were measured during thedeposition process by a quartz crystal microbalance placedclose to the sample holder.

2.2. Characterization of the samples

Fourier transform infrared spectra were recorded with aresolution of 4 cm�1 using a Jasco FT-IR 660 Plus spec-trometer. The sample cell and the interferometer wereevacuated for removing the signals of water and atmo-spheric gasses. The surface morphology of the sampleswas investigated in air by a no-contact-mode AFM modelC-21 (Danish Micro Engineering), mounting a DualScopeProbe Scanner 95-50. In agreement with previous works[18,19], AFM was also used to measure the thickness ofthe samples. UV-visible absorption spectra were performedwith a resolution of 1 nm using a Jasco V-570 dual-beamspectrophotometer. Emission spectra were recorded witha spectral band width of 1 nm through a Jasco FP6300

Figure 1. Chemical structure of Eu(TTA)3phen (top) and paryleneC (bottom).

Luminescent solar concentrators employing parylene films M. Tonezzer et al.

Prog. Photovolt: Res. Appl. (2014) © 2014 John Wiley & Sons, Ltd.DOI: 10.1002/pip

spectrofluorometer in front-face geometry by collecting thefluorescence light from the surface exposed to the excita-tion beam. The acquired data were corrected by consideringthe spectral response of the detection system.

Luminescent solar concentrator performances weremeasured using a 300W solar simulator (Lot-Oriel) withan AM 1.5 radiation. The uncoated bottom face and threelateral faces were put in contact with blackened surfaceswhile the fourth lateral face was coupled to a 50 × 5mmsilicon cell by means of an optical silicone oil grease.

3. RESULT AND DISCUSSION

3.1. Film deposition

In agreement with the parameters of parylene matrix depo-sition, the co-sublimation of Eu complex was conducted atP= 3 Pa. The deposition rate of Eu(TTA)3phen was cali-brated in order to analyze the feasibility of the evaporationprocess and find the deposition parameters. Table I showsthe Eu(TTA)3phen deposition rates, expressed as the num-ber of moles deposited per surface and time units, as afunction of the crucible temperature.

The data demonstrated that Eu(TTA)3phen compoundcan be sublimated in coarse vacuum and that the depositionrate is strongly influenced by the crucible temperature in-creasing more than 2.5 times when temperature increasesfrom 172 to 178 °C. The deposition rate as a function ofthe crucible temperature can be fit by the following func-tion [20,21]:

Log D ¼ A� B

T

whereD is the deposition rate expressed in moles cm�2 s�1,T is the absolute temperature expressed in K, and A and Bare constants determined by the fits and value, respectively18 and 1.3 × 104K.

The comparison with literature data finally highlightsthat Eu(TTA)3phen compound sublimates at temperaturessignificantly lower than commercial dyes: for example,Lumogen Red (LR305) compound in coarse vacuum sub-limates at 270 °C [15]. Moreover, the accurate calibrationof the Eu(TTA)3phen deposition rate increase with the

crucible temperature allows to perform highly controlledgrowing process.

In order to establish a precise and reproducible co-sublimation process, the deposition rate of parylene wasalso measured and an average mass deposition rate of56.5 ng/s * cm2 (±5%) was found. This value correspondsto a molar deposition rate, obtained by assuming theParylene C monomer (M.W. = 138.62) as elementary unit,of 4.1 × 10�10 moles/s * cm2.

After defining the deposition parameters (P= 3 Pa,T= 178 °C), several Eu complex-containing parylene filmswere produced by co-sublimating Eu complex andparylene C dimer. Five films with different thicknesseswere obtained by multiple deposition runs. Table II reportsthe nomenclature, the deposition parameters, and the mainparameters of the samples produced in this work.

The co-sublimation process allows conduction of well-controlled and reproducible growing processes and placesitself as a novel promising technique for producing high-efficiency luminescent films. In particular, the knowledgeof deposition rates of host and guest components allowsto accurately control the growing rate, the thickness, andthe dye concentration of the films.

As it was the first time that Eu(TTA)3phen-containingparylene films were produced, their properties were widelyinvestigated. The chemical properties of the films wereassessed through FT-IR analysis (Figure 2).

The parylene matrix is responsible of the peaks at 2860and 2925 cm�1, due to symmetric and anti-symmetricstretching vibrations of sp3 and sp2 C–H bonds, and ofthe peak at 3019 cm�1 due to the C–H stretching modesof aromatic hydrocarbons. The integrity of the Eu(TTA)

3phen molecules within the sample is confirmed by thepresence of all the characteristic peaks of Eu(TTA)3phen[22]. In fact, the good coordination of Eu ion to the ligandsvia the C═O (TTA) and N atoms (phen) is demonstratedby the peaks at 1625 and 1600 cm�1 (C═O stretchingvibrations), at 1539 cm�1 (C═N phenantroline stretchingvibrations), at 845 (C–C phenantroline ring vibrations),and at 725 cm�1 (C–H phenantroline bending vibrations)[23]. The integrity of the sublimated Eu(TTA)3phenmolecules is confirmed by the optical emission spectrumof the vacuum-evaporated film, which shows the charac-teristic peaks of the pristine compound, as followingreported.

The surface roughness of the samples was investigatedby AFM microscopy. Figure 3, which shows the AFM im-age of sample S1600, highlights that the Eu(TTA)3phen-containing parylene films are characterized by lowroughness (Ra = 3.8 nm; Rq= 3.7 nm). The surface flatness,which permits to minimize the light scattering at the air/filminterface, represents a strategic feature for developingefficient LSC devices. At this regard, it is significant to un-derline that the roughness is not affected by the thickness ofthe samples (Table II).

Figure 4 shows the absorption and emission spectra ofsample S320: the optical spectra of Eu film are alsoreported for comparison.

Table I. Deposition rate of Eu(TTA)3phen at P=3Pa.

Temperature (°C) Deposition rate (10�13 moles cm�2 s�1)

172 6.7173 8.0174 11.6175 17176 25.3177 32.8178 38.9

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S320 and Eu films show absorption spectra rangingfrom 250 to 400 nm. The absorption of Eu(TTA)3phen–parylene-containing samples in the 250–300 nm windowavails itself of the presence of parylene matrix, which ab-sorbs in that region. This result is significant: in fact,

parylene matrix by absorbing UVB rays allows to improvethe radiation hardness of Eu(TTA)3phen molecules and topreserve the optical properties of PMMA waveguide.

S320 film shows the Eu(TTA)3phen characteristic emis-sion peaks at 580, 591, 613, and 652 nm due, respectively,to the transition 5D0-

7 F0,5D0-

7 F1,5D0-

7 F2, and5D0-

7 F3of the Eu ion. In particular, Eu(TTA)3phen-containingparylene films are characterized by a Stokes shift (approxi-mately 300 nm) much larger [25,24] than common organicdyes such as Rhodamine 6G (21 nm) [25] and LumogenRed (33 nm) [15,26] Large Stokes shift implies the absenceof absorption in the emission region of Eu(TTA)3phen-containing parylene samples and is strategic in LSC fieldfor developing novel devices free from self-absorptionlosses. Moreover, it is important to note that the main emis-sion peak of sample S320 (613 nm) is much higher than thatof Eu film.

This superiority was analyzed by normalizing the lumi-nescence intensity of S320 and Eu samples on the absorp-tion peak intensity at 347 nm, which is due to TTAmolecules and depends on the quantity of Eu(TTA)3phenmolecules involved in the luminescence process. Whilethe absorption intensity of S320 film at 347 nm is similarto that of Eu one, the ratio of S320 and Eu emissionintensities at 613 nm is more than double. This means that,under the same quantity of Eu complex, S320 film shows aluminescence more than two times higher than Eu sample.

Table II. Nomenclature and principal features of the films produced in this work.

Sample Eu PARY S320 S640 S960 S1280 S1600

Thickness (nm) 322 646 964 1288 1612Eu(TTA)3phen surface concentration (mg cm-2) 0 0.045 0.089 0.134 0.179 0.224Position of main absorption peak (nm) 347 290 290 290 290 290 290

347 347 347 347 347Absorbance at 347 nm 0.155 0.084 1.326 2.848 saturated saturated saturatedPosition of main emission peak (nm) 613 360 613 613 613 613 613

380Roughness Rq (nm) 3.5 3.7 3.6

Figure 2. Fourier transform infrared spectra of parylene film(PARY), Eu(TTA)3phen vacuum-evaporated film (Eu), and Eu

(TTA)3phen-containing parylene film S320.

Figure 3. Atomic force microscopy morphology of Eu(TTA)

3phen-containing parylene film S1600.

Figure 4. Absorption (abs) and emission (em) spectra of Eu(TTA)3phen–parylene-containing sample S320 (S320) and Eu

(TTA)3phen (Eu) film (T=20 °C, λex = 270 nm).

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This much higher luminescence can be explained consider-ing two different effects: (i) Eu(TTA)3phen molecules areuniformly dispersed in the parylene matrix; therefore,quenching effects are prevented and (ii) parylene plays anactive role in the luminescence process. In fact, asevidenced by Figure 5, parylene exhibits an intrinsic emis-sion in the (340–425 nm) window: the photons emitted byparylene matrix are absorbed by the TTA molecules andre-emitted at the characteristic emission peaks going from582 to 652 nm by Eu atoms. This host–guest energy trans-fer can be noted by comparing the shape of the emissionspectra of S1600 and PARY samples. In particular, it ispossible to note that the emission intensity ratio betweenthe peaks at 360 and 380 nm of S1600 sample (0,77) issensitively lower than that of sample PARY (0,96). Theabsorption spectrum of Eu(TTA)3phen complex clearlydemonstrates that the Eu(TTA)3phen molecules absorbpart of the photons emitted by parylene.

The data demonstrate that the role of the parylenematrix is innovative and strategic in LSC field. In fact, itabsorbs UVB rays allowing to shield both Eu(TTA)3phenmolecules and PMMA substrates from their interactionand, at the same time, it improves the final performancesof the devices by allowing a better conversion of the UVwindow of the solar spectrum. It is worth to underline thatthis kind of PV devices, being transparent in the visibleregion, is qualified for working as PV windows. Moreover,as several other dyes can be co-sublimated into parylenefilms, the approach used in this work can open theway for the production of a new class of improvedLSC materials.

3.2. I–V performances of LSCs under AM1.5G

In order to evaluate the performances of the produced LSCs,the I–V curves under AM 1.5G solar illumination were mea-sured: Figure 6 shows the output power of the devices as a

function of the thickness of the Eu(TTA)3phen-containingparylene films.

The LSC power increases with the thickness of the filmsup to the maximum thickness (1600 nm), as the Eu(TTA)

3phen surface concentrations of the films (ranging from0.45 × 10�4 g/cm2 to 2.24 × 10�4 g/cm2) are not enough tocompletely absorb the solar radiation in the absorption re-gion of Eu(TTA)3phen. This finding agrees with other lit-erature data in which the minimum Eu(TTA)3phenconcentration for assuring the full absorption is indicatedto be 4.2 × 10�4 g/cm2 [27]. It is worth to note that theLSC output power linearly increases with the filmthickness: this behavior testifies that every Eu(TTA)3phenmolecule gives the same contribute to the LSC powerindependently by its distance from the PMMA substrateand indicates that the Eu(TTA)3phen-containing parylenefilms are not affected by self-sorption losses.

Table III reports the main parameters of sample S1600.The optical efficiency (ηopt) and the power conversion

Figure 5. Absorption spectrum of Eu(TTA)3phen (Eu, abs) filmsand emission spectra of Eu(TTA)3phen–parylene-containing(S1600, em) and parylene films (PARY, em) over the

310–420 nm window (T=25 °C; λex = 270 nm).

Figure 6. Output power of Eu(TTA)3phen-containing parylene-based luminescent solar concentrators as a function of the thick-ness of the films and of the Eu(TTA)3phen surface concentration.Measurements were carried out under solar simulator atAMG1.5, T=25°. The line represents the linear fitting of the curve.

Table III. Features and electrical parametersof Eu(TTA)3phen-containing parylene-based

S1600 luminescent solar concentrator.

Sample S1600

Substrate PMMALSC sizes (mm3) 50*50*5Cell siliconηcell (%) 14.3Jsc (mA) 4.34Voc (mV) 438FF 0.63ηopt (%) 2.47ηLSC (%) 0.19

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efficiency (ηLSC) were calculated according to the defini-tions reported in literature [15,28]

The comparison with literature data [27] shows thatS1600 sample is characterized by a power conversion effi-ciency (ηLSC) 50% higher than conventional Eu(TTA)

3phen-based LSCs. This result is even more importanttaking into account that the Eu(TTA)3phen surface concen-tration of sample S1600 (2.24 × 10�4 g/cm2) is much lowerthan that of the literature samples (4.2 × 10�4 g/cm2). Thesuperiority of Eu(TTA)3phen-containing parylene filmsclearly demonstrates the good quality of the parylene-based luminescent films, in which Eu(TTA)3phen mole-cules are finely dispersed, and the active role of parylenematrix in improving the LSC external quantum efficiencyby absorbing UV light and transferring it to Eu(TTA)3phenmolecules. The photons not re-absorbed by Eu complexare moreover transmitted within the waveguide bringingan additional contribute to the efficiency of the device.

The variation of the electrical characteristics as a func-tion of the LSC size is a very important feature in LSC fieldin order to analyze the feasibility to produce large sizemodules. In agreement with other works [29,27], in thiswork, it was in depth investigated through the setup de-scribed in Figure 7a. In this setup, the illuminated areawas changed using a black blind placed on the top of theLSC device. I–V measurements were recorded for eacharea size ranging from 5 to 25 cm2. Figure 7b displaysthe open-circuit voltage, Voc, and the short-current density,Jsc, measured for each particular illuminated area of thefluorescent concentrator.

The voltage increases with increasing size becausemore light reaches the collector. The total current also in-creases while the short-circuit current density (Jsc) slightlydecreases with increasing area.

Nevertheless, it is important to note that Jsc of Eu(TTA)

3phen-containing parylene-based LSCs decreases app-roximately ten times lower than the dye-based LSC [29].This feature is strategic for developing competitive LSCdevices and is related to the absence in these devices of

self-sorption losses. In fact, Jsc is related to the probabilityfor a photon emitted in a position of the LSC device toreach the solar cell placed on the edge: the large Jsc de-crease occurring in dye-based LSC is due to the parasiticre-absorption and re-emission events, which become morelikely to happen with increasing path length of the photon.The slight Jsc decrease of Eu(TTA)3phen-containingparylene-based LSCs can be attributed to the host absorp-tion losses of PMMA slab.

The most significant performance in evaluating a LSCdevice is the trend of the power conversion efficiency(ηLSC) as a function of the size. The ηLSC variation of Eu(TTA)3phen-containing parylene-based and dye-basedLSCs was normalized and reported in Figure 8.

The comparison clearly shows that while the dye-basedLSC is characterized by an average efficiency decrease of2.5% every cm2, Eu-based LSCs are characterized by an

Figure 7. (A) Sketch of setup used for measuring the variation of I–V performance of luminescent solar concentrator with differentradiation area. The radiation area was changed by 1 cm steps by using a covering black blind. (B) Short-circuit current, Jsc (black),and open-circuit voltage, Voc (red), of S1600 LSC as a function of the radiation area. Measurements performed with solar simulator

under AM1.5G.

Figure 8. Variation of normalized power conversion efficiency(ƞLSC) of S1600-based (black) and dye-based (red) luminescentsolar concentrators (LSCs) as a function of the illuminated areaof LSC. Dye-based LSC data were extrapolated by Goldschmidt

et al. [29].

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Prog. Photovolt: Res. Appl. (2014) © 2014 John Wiley & Sons, Ltd.DOI: 10.1002/pip

average efficiency decrease 25 times lower (0.1% everycm2). This result, which is due to the absence of self-absorption losses, is really significant because it gives wayto the possibility to produce large size LSC devices charac-terized by the same electrical features of small samples.

4. CONCLUSIONS

In this work, new Eu(TTA)3phen-containing parylene thinfilms were grown by a new solvent-free co-depositionprocess on PMMA substrates in order to produce novel lu-minescent solar concentrators.

The feasibility of the deposition process was demon-strated for the first time, and the calibration of the processwas performed. The features of the samples were analyzedby infrared analysis (FT-IR), AFM, optical absorption, andemission spectroscopy. FT-IR analysis demonstrated theintegrity of the vacuum-sublimated Eu(TTA)3phen mole-cules within the films. AFM measurements showed thevery flat surface of the films (Rq = 3.7 nm), which is strate-gic in LSC devices for minimizing the light scattering atthe air/film interface. The optical analyses highlighted thatthe absorption and luminescence spectra of the rare earthcomplex are not affected by the matrix interaction preserv-ing the peculiar large Stokes shift (270 nm) of Eu(TTA)

3phen compound. Moreover, the occurring energy transferprocess between parylene and Eu complex stronglyimproves the final luminescence of the sample: in fact,with an equal quantity of Eu complex, Eu(TTA)3phen-containing parylene films show a luminescence more thandouble with respect to conventional Eu(TTA)3phen films.

The current–voltage (I–V) capabilities of samplesshowed that, for the same quantity of Eu complex, Eu(TTA)3phen-containing parylene films exhibit a currentdensity more than two times higher than conventional Eu(TTA)3phen-based LSCs. This result demonstrates the ac-tive role of parylene matrix and the quality of the novelco-deposition process, which allow to grow very flat filmswith finely dispersed luminescent dyes. The I–V perfor-mance of the samples as a function of the radiation areawas finally investigated and compared to those of LSCsemploying conventional dyes. The data highlighted thatthe efficiency of Eu(TTA)3phen-containing parylene filmsdecreases twenty times slower than conventional dye-containing LSCs with the increment of radiation area. Thisresult can be attributed to the absence of overlaps betweenabsorption and emission peaks and is very promising fordeveloping large size LSCs. By considering that numerousother dyes can be co-sublimated within parylene matrices,the approach used in this work can open the way to the pro-duction of a new class of improved LSC materials.

ACKNOWLEDGEMENTS

The research leading to these results received funding fromthe European Community’s Seventh Framework Program

FP7/2007–2013 under grant agreement Marie CuriePCOFUND-GA-2008-226070 (PHOTOFUTURE), undergrant agreement no. 227127(EPHOCELL), and from ThirdCommission of INFN. Michele Tonezzer thanks Prof.Tommaso and Dr. Filippo Maria for their shining mindsand Prof. Federichina for her irreplaceable role.

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Prog. Photovolt: Res. Appl. (2014) © 2014 John Wiley & Sons, Ltd.DOI: 10.1002/pip