Study of Dactylopius opuntiae and its electrical properties as thin film for application in organic devices

Solid State Sciences 102 (2020) 106173

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Study of Dactylopius opuntiae and its electrical properties as thin film for application in organic devices Stefania Llumiquinga a, Kirsty Noboa a, Arthur R.J. Barreto b, Karla Vizuete a, Harold C. Avila c, Alexis Debut a, Marco Cremona, PhD b, *, Yolanda Angulo a a b c

Centro de Nanociencia y Nanotecnología, Universidad de Las Fuerzas Armadas-ESPE, PO BOX 231B, Sangolqui, Ecuador Department of Physics, Pontifícia Universidade Cat� olica do Rio de Janeiro, PUC-Rio, Rio de Janeiro, Brazil Programa de Física, Universidad del Atl� antico, Km 7 Puerto Colombia, Atlantico, Colombia

A R T I C L E I N F O

A B S T R A C T

Keywords: Cochineal Pigment Luminescence Charge carrier transport PHOLEDs

In this work, we perform morphological and physicochemical studies of Dactylopius opuntiae (cochineal) with electron microscopy and explore their use as a transporting layer for organic electronic devices. The charge transport properties of this pigment were investigated through current-voltage measurements. The currentvoltage characteristics have shown that the cochineal can be used as a hole-transporting layer (HTL) with mobility of 5.30 � 0.03 � 10 4cm2V 1 s 1. Different analyses were realized on this pigment and the results were compared with other HTL organic compounds, as Poly(3,4-ethylene dioxy thiophene): poly(styrene sulfonate) (PEDOT:PSS). The results show that the cochineal pigment does not produce luminescence and has a band gap of 2.6 � 0.2 eV with optical absorption in the visible range. The roughness of cochineal thin films was measured after filtering the solution with a value of 11.8 � 0.2 nm. Cochineal and PEDOT:PSS were successfully used as HTL in the fabrication of a [Ir(fliq)2acac] based PHOLED. The results show an increase in the electroluminescent color purity emission due to the filtering action of the natural pigment when compared with the PEDOT:PSS based in this device.

1. Introduction Organic semiconductor devices have witnessed considerable devel­ opment in recent years. Research activities in this kind of materials and their potential applications have quickly increased. One of the aims of this area is to obtain new organic compounds with high-efficiency or new properties for the manufacture of organic light-emitting diodes (OLED) [1], organic photovoltaic cells (OPV) [2,3] transistors (OFETs) [4] and other organic electronic devices. Moreover, synthesizing new molecular structures for the development of charge transporting com­ pounds should be simplified as much as possible, because of the large number of reagents not nature-friendly used during the fabrication process. Thus, it is interesting to analyze the electrical behavior of natural organic compounds to obtain new organic semiconductors with a very simple molecular structure, which may bring high performance, reducing the cost of the devices and to cause less harm to nature. In this paper, we have studied the electrical behavior of Dactylopius opuntiae insects (cochineal), these cochineal species have been identified

early throughout history due to the production of red pigment called carminic acid (CA). Four different species are currently known depending on the growing region [5]. Located mostly in North America, mainly in Mexico [6], its life cycle comprises two states, starting as immature or nymph, followed by the adult state where both male and female have cephalothorax and globose body. One can differentiate the male from the female by the presence of wings in the former. These insects can develop in any part of the plant, fruits, flower calyx and trunk during any stage of host development [8]. They penetrate the cactus with their buccal tract and feed on the sap, remaining immobile [7]. There is currently extensive research concerning the method of CA extraction and applications in the textile industry [9], pharmaceuticals, cosmetics and food [10–14]. Carmine is a low toxicity dye composed of 80% complex of carminic acid extracted from the mealybug and an aluminium-calcium mixture [6]. The chemical compound is stable under light, heat treatments and oxidation; color changes in acid or alkaline solutions and easy to handle [15]. However, information on their physical-chemical composition is limited, as well as detailed studies of

* Corresponding author. E-mail address: [email protected] (M. Cremona). https://doi.org/10.1016/j.solidstatesciences.2020.106173 Received 5 November 2019; Received in revised form 18 February 2020; Accepted 4 March 2020 Available online 11 March 2020 1293-2558/© 2020 Elsevier Masson SAS. All rights reserved.

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Solid State Sciences 102 (2020) 106173

Fig. 1. Schematic representation of the extraction parameters of natural pigment and its molecular structure principal that comprises of cochineal dye.

Dactylopius opuntiae with waxy cover (a)

can be used for the manufacture of organic devices.

Clean Dactylopius opuntiae (b)

2. Experimental 2.1. Materials

CHCl3 for 30min in a sonicator

Cochineal, PEDOT:PSS and [Ir(filq)2acac] organic compounds were used in this work for the manufacture of the organic device. In the case of PEDOT:PSS and [Ir(fliq)2acac], they were used without any addi­ tional purification from Sigma-Aldrich and LUMTEC Corp. The female Dactylopius opuntiae (cochineal) insects in stage of nymphs and adults were obtained in the “Mitad del Mundo” area (0� 010 53.100 S; 78� 270 12.800 W), Pichincha-Ecuador. These insects are found in cactus and they generate a distinct white cottony substance.

Waxy cover (d)

(c)

2.2. Characterization of cochineal

EDS detector

For morphological observation and physical-chemical analysis of the mealybug, there went through a cleaning process with chloroform and sonication (Branson 1510) for 30 min and a scanning electron micro­ scope was used (TESCAN MIRA3 model) with the following detectors: Energy-dispersive X-ray spectroscopy (EDX) and Catodoluminescence. For observation, the samples were fixed with glutaraldehyde 3% for 20 min. Next, the insects were dehydrated in increasing concentrations of ethanol of 50%, 70%, 80%, 90% and 99% for 30 min each and freeze dried for 24 h at constant temperature and pressure of 64 � C and 13 mtorr, respectively. Then, they were placed on conductive sample holders and covered with a thin film of 20 nm of carbon (Sputter Coater Q150R ES) [27].

Fig. 2. Pictures of SEM from Dactylopius opuntaie a) with waxy cover, b) without waxy cover, c) the waxy cover and d) the EDS spectral of waxy cover.

their morphology by scanning electron microscopy (SEM) analysis. The energy gap (Eg) and the ionization potential (IP) of the cochineal sample were estimated with optical spectroscopy (absorption spectral UV–vis) and electrochemical techniques [16]. Based on the values of the HOMO energy level and energy gap obtained from the cyclic voltam­ metry and the optical absorption spectra, respectively, it was possible to determine the rigid band diagram levels for the cochineal sample. On the other hand, in order to explore the electrical behavior of the cochineal’s natural pigment without prior separation of its different compounds, this pigment was used in the manufacture of devices with different electrodes, like Al, LiF/Al, and Indium–Tin-Oxide (ITO), and their per­ formances were compared to other devices using J-V (current density-voltage) characteristics curves [17–21]. Indeed, understanding the carrier transport properties of this natural pigment is of crucial importance to the intended applications. With this aim, we have used an OLED architecture to compare the electrical properties of cochineal dye with the ones of the well-known synthetic dye Poly(3,4-ethylene dioxy thiophene):poly(styrene sulfonate) (PEDOT:PSS) [22–26]. Besides that, the morphologic properties of thin films of this natural pigment were analyzed using atomic force microscopy (AFM). PHOLEDs based on Bis [1-(9,9-dimetil[dimethyl]-9H-fluoreno[Fluorene]-2-il)-isoquinolina [isoquinoline] (acetilacetonato [acetylacetone]) [iridium](III) ([Ir(fil­ q)2acac]) with emission in the red part of the optical spectrum were manufactured as a possible application of cochineal as a hole-transportation layer (HTL), and they were compared with PHO­ LEDs using PEDOT:PSS. An interesting property that will be seen later is that cochineal has an absorption band between 400 and 600 nm, making it possible to use it as a filtering agent in order to further increase the purity of the red emission. Thus, the manufactured device also acts as proof of concept for this filtration property, which would also open new possibilities for this natural compound to be used in solar cells and op­ tical sensors. All these studies can help to understand the carrier type and the possible applications in which this particular natural pigment

2.3. Manufactured and characterization of devices For the manufacture of the organic devices no purification of the mealybug was performed, they were only screened to remove much of the waxy substance and were dried in an oven at 70 � C, approximately, until reaching a constant weight (Fig. 1). The cochineal sample was dissolved in concentration of 0.1 g/ml in water and filtered prior spincoating. In order to determine HOMO energy level, cyclic voltamme­ try (CV) measurements were performed using a three-electrode system. The working electrode was a glassy carbon electrode with a silver and silver chloride (Ag/AgCl) electrode as reference. A platinum strand served as the auxiliary electrode. The glassy carbon working electrode was polished with 0.05 μm alumina powder before each scanning. The analyses were realized in 0.1 M potassium chloride (KCl) solution. Prior to each run, the contents oxygen in KCl solutions was removed by bubbling of N2 for about 15 min. The voltammetry scan rate was 0.05 V 1 at room temperature in the range of 2.0 V–1.5 V (SHE vs. SCE). The optical absorption of the thin film of cochineal and the other organic compounds were analyzed using a UV-VIS spectrometer HP-8452a. More details in the results section. The cochineal and PEDOT:PSS organic thin films were deposited using spin-coating technique on quartz and ITO substrates with a sheet resistance of 10 Ohm sq 1. The spin-coating duration time was always 60s and the speed was varied according to the desired film thickness. The annealing was performed for 15 min at 60 � C. [Ir(fliq)2acac] and the other organic compounds as well as the Al electrode were purchased 2

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Solid State Sciences 102 (2020) 106173

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

Fig. 3. a) Image of the cochineal habitat and microimages of b) adult mealybug, c) ninfa, and its parts d) quinquelocular pore, e) quinquelocular pore wit waxy cover, f) dorsal setae, g) legs, h) antennas, i) oral cavity, j) oral cavity with its extensions and k) ostiolo.

6

x104

(a) Na

Intensity (unit. arb.)

C

Mg

Al

Si

P

S

10.8 1.7 3.5 7.7

4

10.0

Cl

K

Ca

2.6 1.7

30.4 31.3

2

0

K P Si S Cl Ca O MgAl

0

1

2

3

4

(b) 5

Energy (keV)

6

7

8

Fig. 4. EDS analysis of the mealybug, inset percentage of proportion of each element.

from Lumtech Technology and Kurt & Lesker, respectively, and used without any purification. The materials were deposited using a thermal evaporation system from Leybold in a high vacuum environment (base pressure of 5 � 10 4 Pa). The deposition rates were 0.1 nms-1 for organic compounds and 0.3 nms-1 for the metal electrode. Before the de­ positions, all the substrates were cleaned using detergent (Hellmanex

Fig. 5. Analysis of cochineal catodolouminiscence a) without waxy cover and b) with waxy cover.

3

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Solid State Sciences 102 (2020) 106173

40 35

Sample

sample

30 25

Current ( A)

Current ( A)

30

20

20 15 10 5

Blank

0

10

-5

0,0

-0,5

-1,0

-1,5

-2,0

V (SHE vs SCE)

-2,5

0

-10

-20

EHOMO= -0.68Eox-4.4 = -5.02eV 2

1

0

-1

V (SHE vs SCE)

-2

-3

Fig. 6. Cyclic voltammetry of cochineal pigment.

O

Absorption (a.u.)

0,9

O

S

Cochineal insects

0,6

-

SO 3

PEDOT:PSS

Cochineals PEDOT:PSS

0,3

0,0

200

400

600

Wavelength (nm)

800 Fig. 8. The J-V characteristics of ITO/cochineal(500 nm)/LiF:Al(120 nm), in log scale. Inset shows energy levels of device.

Fig. 7. UV–Vis spectra of cochineal pigment and PEDOT:PSS. Inset shows the photograph of cochineals insects and chemistry structure of PEDOT: PSS compound.

Dektak 150). An atomic force microscope (Icon Bruker) was used in the morphology analysis of both cochineal and PEDOT:PSS deposited onto glass substrates with thickness of 110 nm and 150 nm, respectively. In the PHOLED fabrication, the following architecture was employed (thickness in nm): ITO/X (50)/10%wt[Ir(fliq)2acac]:Spiro2CBP (50)/ Alq3 (30)/LiF:Al (120), where X corresponds to the different HTL: cochineal and PEDOT:PSS. The current density (J) vs. voltage (V) was obtained using a Keithley 2400 and a LabView platform for data acquisition. The electroluminescence spectra were measured using a Photon Technology International (PTI) Quanta Master steady state fluorimeter.

Table 1 Energy values of HOMO and LUMO of the samples of cochineal and PEDOT:PSS. Energy HOMO (eV) LUMO (eV)

Cochineal 5.02 2.46

PEDOT 5.20 2.30

III). Next, the substrates were rinsed with deionized water and sonicated in organic solvents (acetone and alcohol). Prior to the deposition they were treated in a UV-ozone chamber for 10min. The thickness of the different layers was measured via profilometer measurements (Veeco,

3. Results and discussion Images of the cochineal with (Fig. 2a) and without (Fig. 2b) cleaning 4

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Solid State Sciences 102 (2020) 106173

Fig. 9. The log J vs. log V characteristics of ITO/cochineal/LiF:Al devices, for different cochineal thickness: 100, 120, 300 and 400 nm.

100

Fig. 11. AFM imagens of 5 μmx5μm of the thin film on glass of cochineal (top), and PEDOT:PSS (bottom).

The chemical composition of the mealybug is mainly K, P, Mg, Cl, Ca, O, C and S (Fig. 4) [31]. Traces of Al and Si can be detected due to residues of the waxy substance in the analyzed insect. The percentages of the elements recorded were determined through several repetitions in different samples. On the other hand, it was observed that the cleaned mealybug does not have electroluminescence when it is irradiated by an electron beam (Fig. 5a), while the insects that did not undergo a cleaning treatment presents a contrast of blue tonality (Fig. 5b), indicating that the elements contained in the waxy substance are the probable cause of this luminescence [32]. Fig. 6 shows the voltammogram of cochineal within a potential window of 2.0 V–1.5 V. In the CV plot there is no detectable peak referred to oxidative or reductive processes. However, it is not uncommon for natural compounds to present a not so well-behaved curve [33–36]. Our case can be an extreme case once the extract was used with no purification process. Besides that, one can see by comparing the sample curve and the blank curve that they have very different signal intensities (Fig. 6, inset). In order to avoid any ambi­ guity, the values were determined using the inflexion point of the first peak noticeable in the second derivative curve of the CV curve (not showed here). The anodic oxidation can be explained by the presence of anthraquinone in the cochineal’s pigment (Fig. 1) that causes an oxygen reduction when it is subjected to such electrical potential [37,38]. From the CV plot it is possible to estimate the HOMO energy for cochineal around 5.02 eV. Fig. 7 shows the absorption spectra of thin films of cochineal and PEDOT:PSS [39,40]. The inset of Fig. 7 shows a cochineal insects picture. Cochineal compound has two main absorption bands, one centered at 280 nm and another, broader, at about 520 nm. Differently, the ab­ sorption bands of PEDOT:PSS occur just in the UV/blue range. PEDOT: PSS was taken as reference and its optical absorption and others physical properties were compared with the natural pigment under study [41, 42]. From the data it was possible to determine the optical gap of the cochineal and PEDOT:PSS. Table 1 summarizes the HOMO and LUMO values of cochineal and PEDOT:PSS. Moreover, in order to investigate the charge transport behavior of cochineal, devices with a simple diode structure ITO/cochineal(500 nm)/LiF:Al(120 nm) were fabricated and their I–V curves are shown in Fig. 8 in a semi log scale together with the rigid band diagram for the

SCLC

10-2

x10-2

J (mA/cm2)

J(mA/cm2)

10-1

-3

10

0.1

0.04

0.03

1

Vbias(V)

3

3.5 4 Vbias (V)

4.5

10

Fig. 10. The log J vs. log V characteristics of Al/cochineal(150 nm)/LiF:Al device. Inset shows the performed fitting and energy levels of device.

show that the whitish waxy coating (Fig. 2c) is in the form of microtubes of 1.3 μm diameter and contains Si, P, Ca and Al (Fig. 2d). The morphology of female mealybugs and their respective nymphs (Fig. 3b and c) found on cactus leaves (Fig. 3a) are the main characteristics of the species Dactylopius opuntiae insects (cochineal). Meaning, the oval body of adult mealybugs (Fig. 3b: length ¼ 3.9 � 0.6 mm; width ¼ 3.6 � 0.8 mm) that contains quinquelocular pores (Fig. 3d: external radius ¼ 2.9 � 0.1 μm and internal radius ¼ 2.2 � 0.1 μm) and a tubular duct (Fig. 3d: radius ¼ 0.76 � 0.02 μm) where they secrete their waxy coating all over their body (Fig. 3e). The truncal setae ridges can identified (Fig. 3f: length ¼ 16.5 � 0.6 μm and width ¼ 5.4 � 0.6 μm) and also the rounded setae (Fig. 3f: length ¼ 22 � 1 μm; width ¼ 2.5 � 0.2 μm). The segmented legs with a single nail (Fig. 3g: length ¼ 0.74 � 0.06 mm) helps the insect to move on the leaves of the plant. In the head it has a pair of antennas with six divisions (Fig. 3h: length ¼ 0.27 � 0.05 mm) and a filamentous mouth (Fig. 3i: length ¼ 0.16 � 0.05 mm and width ¼ 0.12 � 0.04 mm) which consists of 2–3 extensions on average protruding with approximate length of 1 mm (Fig. 3j). In the lower part there is an ostiole charac­ teristic of the species (Fig. 3k: length ¼ 0.15 � 0.02 mm; width ¼ 0.21 � 0.01 mm) as stated in the literature [29,30]. 5

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Solid State Sciences 102 (2020) 106173

transporting material with mobility of 5.30 � 0.03 � 10 4 cm2 V 1 s 1 [44]. Fig. 11 shows the AFM image in the tapping mode of thin film of cochineal and PEDOT:PSS, it is possible to observe clusters and a roughness of 11.8 � 0.2 nm and 4.9 � 0.3 nm was measured, respec­ tively. Fig. 12 shows (a) the electroluminescence spectra of the [Ir(fli­ q)2acac] based PHOLEDs fabricated with cochineal and PEDOT:PSS as HTL, inset shown the CIE chromaticity diagram of the devices. In Fig. 12 (b) the J – V characteristics of the fabricated PHOLEDs are presented. In the same Figure, it is shown the rigid band diagram and a picture of each device. In a PHOLED, it is important to have a phosphorescent compound with color purity, in the case of the compound [Ir(fliq)2acac] dissolved in chloroform registered (x, y) coordinates in (0.714, 0.285) (Fig. 12a) with λmax ¼ 652 nm. Even with a current density 13.7 � 0.7% lower than the device using PEDOT:PSS, the PHOLED device using cochineal as HTL presented a purer red emission with (x; y) coordinates of (0.695; 0.2993), very close to the red color of [Ir (fliq) 2acac] when compared to the device using PEDOT: PSS (0.586; 0.378).

[Ir(fliq)2acac]

N

S

(b)

CH3

Ir

O O CH3

PEDOT:PSS COCHINEALS

4. Conclusion

0

10

We demonstrated that is possible to use a natural pigment as a simple, cost-effective, easily reproducible at room temperature, without any pollutant solvent for application in the manufacture of organic de­ vices. The detailed morphological and physicochemical study of the mealybug by electronic microscopy and its EDS and catodoloumi­ niscence analysis helped to determine the exact size of the parts constituting the Dactylopius opuntiae insects and its chemical elements. Cochineal and PEDOT:PSS were successfully used as HTL in the fabri­ cation of a [Ir(fliq)2acac] based PHOLED. The cochineal’s natural pigment without prior purification was shown to be a hole transporting material with a high detection of photons in the UV–Vis, having no electroluminescence between 400 nm and 800 nm (Fig. 4a). With color purity of 97% in the electroluminescence of the manufactured [Ir(fli­ q)2acac] PHOLED, meaning an increase in the electroluminescent color purity emission due the filtering action of the natural pigment with respect to the PEDOT:PSS based device. Furthermore, the natural pigment has a charge mobility that is just one order of magnitude lower than that of PEDOT:PSS [41]. Probably, the mobility value can be increased reducing the roughness and the cluster formation in the cochineal thin film.

2

J (A/cm )

-1

10

-2

10

Cochineal PEDOT:PSS

-3

10

-4

10

0,1

1

Vbias (V)

10

100

Fig. 12. (a) Left: UV–Vis spectra from cochineal pigment and right: electrolu­ minescence spectra from [Ir(fliq)2acac] devices, using as HTL the cochineal (50 nm) or PEDOT:PSS (50 nm). Inset shows CIE chromaticity diagram. (b) The log I vs. log V characteristics of PHOLED in room temperature. Inset shows energy levels of devices and device pictures using as HTL Cochineal or PEDOT:PSS.

diode. In Fig. 8, the devices fabricated with four times filtered solution (higher purity) show an increase in the current (about 50%) with respect to that twice filtered. In Fig. 9 the J-V characteristics of four ITO/cochineal/LiF:Al devices are shown in a log-log scale. Here, the thickness of the cochineal films was varied using 100, 120, 300, and 400 nm. As expected, the current increases as the thickness decreases. However, even in the case of the thickest film the current density is sufficiently high to show good transport behavior. In order to estimate the charge mobility, devices with the structure ITO/cochineal(150 nm)/Al were fabricated. Fig. 10 shows the representative J - V electric characteristics of the device plotted in a log-log scale. The estimated mobility was extracted following the method described in [43]. In the SCLC regime it is possible to use equation (1) to estimate the value of the charge mobility: rffiffiffi ! 9 V2 V JSCLC ¼ ε 3 μ0 ⋅exp 0:89γ (1) 8 d d

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement Stefania Llumiquinga: Investigation, Visualization, Writing - orig­ inal draft. Kirsty Noboa: Investigation, Visualization, Writing - original draft. Arthur R.J. Barreto: Investigation, Validation, Writing - original draft, Writing - review & editing. Karla Vizuete: Visualization, Data curation. Harold C. Avila: Investigation, Data curation. Alexis Debut: Visualization, Data curation, Writing - review & editing. Marco Cre­ mona: Resources, Funding acquisition, Supervision, Writing - review & editing. Yolanda Angulo: Conceptualization, Validation, Formal anal­ ysis, Investigation, Writing - original draft, Visualization, Supervision.

where ε is the vacuum permittivity multiplied by the permittivity of the organic compounds (typically considered three times ε0), d the thickness of the device, J the current density, V the applied voltage, γ is the mobility coupling with the electric field and μ0 is the mobility at zero field. These curves indicate that cochineal can be considered as a hole-

Acknowledgements The authors are grateful to the Brazilian agencies CNPq, FAPERJ, CAPES, INCT- INEO, PUC-Rio and FAPESP for financial support. We also 6

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Solid State Sciences 102 (2020) 106173

thanks the Center of Nanoscience and Nanotechnology of the Uni­ versidad de las Fuerzas Armadas ESPE for her technical supports.

[22] M. Petrosino, A. Rubino, Synth. Met. 161 (2012) 2714–2717. [23] Xiaolong Zhu, Wallace C.H. Choy, ChunhuiDuan FengxianXie, Chuandao Wang, Wenlei He, Fei Huang, YongCao; Solar Energy Materialsand Solar Cells 99 (2012) 327–332. [24] Claudio Zuliani, Dermot Diamond GiusyMatzeu, Talanta 125 (2014) 58–64. [25] Soo Won Heo, Kyeong Hoon Baek, Tae Ho Lee, Joo Young Lee, Doo Kyung Moon, Org. Electron. 14 (2013) 1629–1635. [26] Amare Benor, Shin-yaTakizawa, C�esar P�erez-Bolívar, Pavel Anzenbacher Jr., Org. Electron. 11 (2010) 938–945. [27] S. Guerra, A. Debut, Comparaci� on entre cuatro protocolos para la preparaci� on de muestras de referencia usando el Microscopio Electr� onico de Barrido, Ciencia y Tecnología ISSN:1390-4663, 2012. Universidad de las Fuerzas Armadas, CENCINAT, Sangolquí, Pichincha, Ecuador. [29] P� erez Guerra Gema María del Carmen, Biosystematics of the Family Dactylopiidae (Homoptera: Coccinea) with Emphasis on the Life Cycle of Dactylopius Coccus Costa; Thesis Doctor of Philosophy in Entomology; Virginia Polytechnic, 1991 (Virginia). [30] L.E. Claps, M.E. y de Haro, Cocoidea (insecta: Hemiptera) associated with cactaceae in Argentina, Journal of the Professional Association for Cactus Development 4 (2001) 77–83. [31] A. Bach, J. Soles, F. Roger, T. Perú, bliote de Ingiería uímica liote de IngenieBim, 2006. [32] E. Crespo-feo, Catodoluminiscencia Espectral ( CL-ESEM ) de una Cerusita Fibrosa, 2010. [33] K. Gonz� alez Arzola, M.C. Ar�evalo, M.A. Falc� on, Catalytic efficiency of natural and synthetic compounds used as laccase-mediators in oxidising veratryl alcohol and a kraft lignin, estimated by electrochemical analysis, Electrochim. Acta 54 (9) (2009) 2621–2629. [34] A. Simic, D. Manoilovic, D. �segan, M. Todorovic, Molecules 12 (2007) 2327–2340. [35] Jesús F. Arteaga, et al., Comparison of the simple cyclic voltammetry (CV) and DPPH assays for the determination of antioxidant capacity of active principles, Molecules 17 (5) (2012) 5126–5138. [36] Romana Sokolova, et al., The oxidation of natural flavonoid quercetin, Chem. Commun. 48 (28) (2012) 3433–3435. [37] PiotrPipka TadeuszOssowski, Liwo Adam, DanutaJeziorek, Electrochim. Acta 45 (2000) 3581–3587. [38] Nadine Seidel, Torsten Hahn, Liebing Simon, Wilhelm Seichter, Jens Kortus, Edwin Weber, New J. Chem. 37 (2013) 601–610. [39] Mingtao Li, Wenlian Li, Wenming Su, Faxin Zang, Bei Chu, Xin Qi, Defeng Bi, Bin Li, Tianzhi Yu, Solid State Electron. 52 (2008) 121–125. [40] A. Stelios, Choulis, vi-en choong, aditee patwardhan, mathew k. Mathai, and franky so, Adv. Funct. Mater. 16 (2006) 1075–1080. [41] S.A. Rutledge, A.S. Helmy, J. Appl. Phys. 114 (2013) 133708. [42] Chen Song, Zhiming Zhong, Zhanhao Hu, Yu Luo, Lei Wang, Jian Wang, Yong Cao, Org. Electron. 43 (2017) 9–14. [43] James C. BLAKESLEY, et al., Towards reliable charge-mobility benchmark measurements for organic semiconductors, Org. Electron. 15 (6) (2014) 1263–1272. [44] S.A. Rutledge, A.S. Helmy, J. Appl. Phys. 114 (2013) 133708.

References [1] G. Krucaite, L. Liu, D. Tavgeniene, L. Peciulyte, J.V. Grazulevicius, Z. Xie, B. Zhang, S. Grigalevicius, Opt. Mater. 42 (2015) 94–98. [2] Junliang Yang HaichaoDuan, Lin Fu, Bingchu Yang JianXiong, Jun Ouyang, Han Huang ConghuaZhou, YongliGao, Thin Solid Films 574 (2015) 146–151. [3] SolennBerson CyrilChappaz-Gillot, BalthazarLech^ene RaulSalazar, DmitryAldakov, VincentDelaye, St�ephaneGuillerez, ValentinaIvanova, Sol. Energy Mater. Sol. Cell. 120 (2014) 163–167. [4] Huiyue Tan, AoLiu GuoxiaLiu, FukaiShan ByoungchulShin, H. Tan, et al., Ceram. Int. 55 (2015) 1–7. [5] D. Miller, A. Rung, G. Parikh, G. Venable, A.J. Redford, G.A. Evans, R.J. Gill, Scale Insects, Edition 2, USDA APHIS Identification Technology Program (ITP), Fort Collins, CO, 2014 [date of access], http://idtools.org/id/scales/. [6] K. Lech, K. Witk� os, B. Wilenska, M. Jarosz, Identification of unknown colorants in pre-Columbian textiles dyed with American cochineal (Dactylopius coccus Costa) using high-performance liquid chromatography and tandem mass spectrometry, Anal. Bioanal. Chem. 407 (3) (2015) 855–867. [7] H.E. Nejad, A.E. Nejad, Cochineal (Dactylopius coccus) as one of the most important insects in industrial dyeing 1 (11) (2013) 1302–1308. [8] C. Hosts, Neotropical Entomology 40, 2011, pp. 62–71, 1. [9] H. Schweppe, H. Roosen-Runge, in: R.L. Feller (Ed.), Artists’ Pigments: A Handbook of Their History and Characteristics vol. 1, Oxford University Press, Washington, 1986, p. 255. [10] Q. Khadijah, M. Heba, Environmental production of fashion colors from natural dyes, Int. J. Phys. Sci. 8 (16) (2013) 670–683. [11] M� onica Gonz� alez, M. Gloria Lobo, Jesús M� endez, Aurelio Carnero; FoodControl 16 (2005) 105–112. [12] Mohammad Shahid, Shahid-ul-Islam, Faqeer Mohammad, J. Clean. Prod. 53 (2013) 310–331. ~ ez, Food Chem. 132 (2012) [13] M.E. Borges, R.L. Tejera, L. Díaz, P. Esparza, E. Ib� an 1855–1860. [14] Evangelina A. Gonz� alez, Elisa M. García, M� onica A. Nazareno, Food Chem. 119 (2010) 358–362. [15] G. Arroyo, G. Ruiz, L. Vargas, G. Rodríguez, Aplicaci� on de productos derivados del insecto Dactylopius coccus Costa (Hom� optera, Dactylopiidae), vol. 20, 2010, pp. 51–55, 120. [16] C. Stael, R. Cruz, B. Naranjo, A. Debut, Y. Angulo, Improvement of cochineal extract (Dactylopius coccus costa) properties based on the green synthesis of silver nanoparticles for application in organic devices, J. Nanotechnol. (2018) 11. [17] P.W.M. Blom, M.C.J.M. Vissenberg, Mater. Sci. Eng. 27 (2000) 53–94. [18] L.S. Roman, I.A. Hümmelgen, F.C. Nart, L.O. P�eres, E.L. de Sa, J. Chem. Phys. 105 (1996) 23. [19] Mario Petrosino, Alfredo Rubino, Solid State Commun. 149 (2009) 1822–1825. [20] P.W.M. Blom, M.J.M. de Jong, J.J.M. Vleggaar, Appl. Phys. Lett. 68 (1996) 23. [21] J.P. Rasimas, K.A. Berglund, G.J. Blanchard, J. Phys. Chem. 100 (1996) 7220–7229.

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