We report a facile method to fabricate an AZO/PANI heterostructure by a sandwiching technique. Aluminum-doped ZnO (AZO) films were deposited onto indium tin oxide (ITO) glass using the sputtering technique while PANI films were deposited onto ITO glass using electropolymerization. The optoelectric properties of the inorganic/organic device were characterize

AbdulAlmohsin, S.

Al-Mutoki, S. M.

Li, Z.

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 66 Article 8 2012 Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar Cells S. AbdulAlmohsin University of Arkansas at Little Rock, samir_mahdi47@yahoo.com S. M. Al-Mutoki Technical Institute Of Shatrah Z. Li University of Arkansas at Little Rock Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the Biological and Chemical Physics Commons Recommended Citation AbdulAlmohsin, S.; Al-Mutoki, S. M.; and Li, Z. (2012) "Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar Cells," Journal of the Arkansas Academy of Science: Vol. 66 , Article 8. DOI: https://doi.org/10.54119/jaas.2012.6601 Available at: https://scholarworks.uark.edu/jaas/vol66/iss1/8 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. Journal of the Arkansas Academy of Science, Vol. 66, 201226Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar CellsS. AbdulAlmohsin1*, S.M. AL-Mutoki2 and Z. Li11Department of Physics, University of Arkansas, Little Rock, AR 72204,USA2Electrical Department, Foundation Of Technical Education, Technical Institute Of Shatrah,Shatrah, ThiQar00964, Iraq*Correspondence: samir_mahdi47@yahoo.comAbstractWe report a facile method to fabricate anAZO/PANI heterostructure by a sandwichingtechnique. Aluminum-doped ZnO (AZO) films weredeposited onto indium tin oxide (ITO) glass using thesputtering technique while PANI films were depositedonto ITO glass using electropolymerization. Theoptoelectric properties of the inorganic/organic devicewere characterized.IntroductionTransparent conductive oxides (TCOs) have a widerange of applications in many fields such as gassensors (Gupta et al. 2010), piezoelectric (Lorenz-Hallenberg 2003), solar cells (Sittinger et al. 2008) andas transparent conductive electrodes (Shi et al. 2000).TCOs have unique properties that combine both hightransparency and high conductivity. In the majority ofsemiconductors, conductivity and transparency arerepulsive and oppose each other. In TCOs, the largeband gap (≈ 3.4 eV) makes them transparent to the region of interest in the solar applications and the non-stoichiometry (lack of oxygen) results in high freecharge concentration and then high conductivity.Indium tin oxide (ITO) is widely and commerciallyused as TCO material, but indium is a scarce elementon Earth, and is toxic. Another drawback of ITO is thatit has low chemical stability. Aluminum-doped zincoxide (AZO) has attracted increasing interest over theyears and has been investigated as an alternative toITO because it exhibits high transmittance (> 90%) andlow resistivity (around 10-4 Ohm.cm) (Jin et al. 1993).AZO is supposed to be less expensive than ITO andalso less toxic. As with any TCO materials, AZO is ann-type semiconductor in nature, with a bandgap around3.4 eV (Jung et al. 2009). AZO films can be preparedby different methods, such as spray pyrolysis (Kaid etal. 2007), and sputtering (Kong et al. 2011). Sputteringis a common way to deposit AZO by using ZnO andAl2O3 targets and sometimes by using two separatetargets of Al and ZnO (Fenske et al. 1999). Recently,AZO nanoparticles (NPs) have attracted increasingattention (Benouis et al. 2007) as a result of the rapiddevelopment of nanotechnology and nanomaterials.One of the promising applications of AZO NPs is theproduction of efficient solar converters because theNPs films introduce a large junction area in solar cells.Polyaniline (PANI) is one of the best, facile andconductive polymers (Rimbu et al. 2006) with feasiblestability against the environment (Ansari et al. 2006).Its conductivity arises from the -electron conjugate inthe polymeric chain. PANI is naturally a p-typematerial with an optical band gap of about 3 eV. As apolymer, the energy gap diagram of PANI is notcomprised of conduction and valence bands, but ratherit is described by the highest occupied molecularorbital (HOMO) and the lowest unoccupied molecularorbital (LUMO). The HOMO level of PANI is 7.7 eV,while the LOMO level is 4.7 eV. (Catedral et al. 2004).PANI can be synthesized by different techniques, suchas plasma enhanced polymerization (Sadia et al. 2009)and electrochemical techniques (Martinez et al. 2008).Recently, hybrid inorganic/organic heterojunctiondevices have received much attention as promisingjunctions for many applications, such as gas sensors(Gong et al. 2010), light emitting diodes (He et al.2010), and photo detectors (Mahmoud 2009).ZnO/PANI has gained a lot of interest for itsluminescence properties (Amrithesh et al. 2009) andUV detection (Moreira et al. 2009). In this paper,AZO/PANI heterostructure sandwiched between twoITO-coated glass was studied. AZO films weredeposited using the sputtering technique while PANIfilms were deposited using by electro polymerization.The AZO films in solar cells are used as a windowlayer and an active material.MethodsAniline monomer was distilled twice underreduced pressure before use, and dissolved into a 1 Msulfuric acid to make a 0.1 M solution. The polyanilinewas synthesized with a galvanostatic step method at aconstant voltage of 3 V. The working electrode was a26Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8Published by Arkansas Academy of Science, 2012commercial ITOpaper clipofweighing the working electrodeelectro depositiondiagrampolymerizationwiththe range 24 mto 0.076impuritywas kept at0.101 AtimeFigureprepare the PANIsandwiching themensurePANI,electrochemical process when the PANI was still wetA schematic diagramillustrated in Figurecharacunder illumination usingIrradiation was achieved from the TiOthe nanoFiguretheThe AZO filmsputtering poweof1AZO2electrodeposited polyawas used an anode.,40 min. Schematicintimate contact between thethe two films were sandwiched right after theteristics have been investigated in the dark andc. A schematic diagram of theFabrication andwasof the electrochemical cellml/minandfilm and PANIomposite side.used as.torr180vo.thin film.-glass.~.oCltagediagramFigure 1was sputteredr of 150 W30 mAn ZnO disk, theto create2witha counter electrode.ofof the electrochemical cell used toof. Current densityanITOPANIJournal of the Arkansas Academy of Science, Vol. 66, 2012atorrcurrent261 to 202werethe fabricated device isAM1.5 sunlight simulator.ITOAZOCharacterization of Asurface area ofniline was estimated bywithThebrought into contacttheAZObefdisplaysundersubstrate temperaturewas set at-ore and afterontoa flow ratewith 2 wt% AlVheterostructure. ToPANIthe ITO glassAr pressure, with aAZO-voltage2 side and fromheterostructure1.5The amounta schematicfor in situof 0.0750.097 toand thecmsputter(Jluminum2. Athein2O3by.-V).27ResultsAZO NPs using the scanning electron microscopy(SEM).to 100 nm. The film displays a good uniformity withlittle agglomeration.Figure 3. SEM photheterodiodebehavior with a rectification of 28 atstands for the ratio of the forward to reverse current ataindicates the formation of a diode between AZO nfilm and PANI pdiode illustrates a gradual increabreakdiode.behavior of the form:wq/kT is the thermal energy and n is the ideality factor.Figurdevice. The curve exhibits a linear behavior in the biasregion of 0.05diode is:current ofcalculated from this equation is 4.3.ndomina-dopedFigure 3 demonstrates the surface topography ofThe dcertain bias voltage).hereThe equationsuggest-downIeZand DiscussionThe diameter of AZO NPs ranges from 50 nmark JThe fo is the saturation current, V is the bias voltage,5 represents the semistednO/PANI Hybridshown in Figure, which is a feature of the hete4 ×that the carrier transport of this device isby more thao of AZO NPs deposited onto ITO glass.-V characteristics of the AZO/PANI-orward current showsI-0.3 V. The empirical equation of thisI10type film. The reverse current of this0indicate-5 A, while the ideality factor that isexpIo00004.ns an extrapolated saturatone mechanism.The rnkTqVexpSolar Cells4-log Iexhibitectifying behaviorse,87.8±1 V (rectificationreferring to a softan exponential,-V curve of theVThe high value ofa rectifyingrojunction-type(1)(2)ion27Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8https://scholarworks.uark.edu/jaas/vol66/iss1/8DOI: https://doi.org/10.54119/jaas.2012.6601S. AbdulAlmohsin, S.M. Al-Mutoki and Z. LiJournal of the Arkansas Academy of Science, Vol. 66, 2012280.000010.00010.0010.010 0.1 0.2 0.3 0.4Bias Voltage (V)ForwardCurrent(A)Figure 4. Dark I-V characteristics of AZO/PANI heterojunction, y-axis multiply by 10-2.Figure 5. The semi-log I-V plot at the forward bias, Y-Axesmultiply by 10-2.The J-V characteristics of the AZO/PANI thin filmsolar cell exhibit considerable photovoltaicperformance under illumination AM 1.5 (~100mW/cm2), as depicted in Fig. 6, with a short circuitcurrent density (ISC) of 0.075 mA/cm2, an open circuitvoltage (VOC) of 195 V and a fill-factor (FF) of 0.41.The photon conversion efficiency (PCE) of the cell is0.0078%, which indicates a significant performance.The photovoltaic performances of the AZO/PANIdevices under different illumination intensities arelisted in Table 1.The use of the sandwiching technique to fabricate aheterojunction has not been reported in the literature todate and most of the existing papers use the subsequentdeposition of the two layers. The rectification behavior-0.4 -0.2 0.0 0.2 0.4 0.6-0.24-0.120.000.120.24Current(mA/cm2)Voltage(V)ZNO doped ALLight And DarkFigure 6. The J-V characteristics under AM1.5 illumination.and the acceptable photovoltaic performance of thedevice presented above suggest a successful formationof a heterojunction between AZO nanoparticles andPANI, indicating that the sandwiching technique isuseful in the fabrication of this kind of heterojunction.The wet surface of PANI directly after theelectropolymerization helps to form an intimate contactwith AZO nanoparticle film, and the morphology of thebumpy AZO surface could help to increase the junctionarea. An SEM photographs. In the subsequentdeposition, the AZO nanoparticle film needs to be usedas a working electrode. That can cause a degradation ofthe AZO film when it is immersed in the electrolyteand, in addition, the AZO film may dissolve in theelectrolyte because of the effect of the sulfuric acid.Furthermore, the subsequent deposition needs to makeohmic contact onto the PANI surface, requiring the useof the evaporation technique to deposit the metal ontothe PANI surface, which could degrade the PANIperformance.Table 1. The photovoltaic performances of theAZO/PANI devices under different illuminationintensities.Illumination(mW/cm2)WIsc(mA/cm2)Voc(volt)FF PCE(%)100 0.075 0.195 0.41 6.0 ×10-380 0.055 0.18 0.57 7.1 × 10-350 0.04 0.15 0.63 7.6 ×10 -325 0.025 0.15 0.61 9.1 × 10-3The room temperature photoluminescence (PL) ofAZO nanoparticles deposited onto ITO glass is shown-10-8-6-4-20246810-1.5 -0.5 0.5 1.5Bias Voltage (V)DarkCurrent(mA)28Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8Published by Arkansas Academy of Science, 2012Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar CellsJournal of the Arkansas Academy of Science, Vol. 66, 20122910001050110011501200125013002 2.5 3 3.5 4Photon Energy (eV)PLIntensity(au)in Figure 8. The PL spectrum shows a near-band-edgeat 3.46 eV, which represents the direct band gap ofAZO. The deep-level emission appears at 2.27 eV,which represents the defects inside the AZOnanoparticles. The intensity ratio (Inear-band/Ideep-level) isabout 1.8, indicating a very high quality film with highcrystallinity and is higher than previously reportedresults (Kim et al. 2008). The PANI film shows a PLpeak of 2.9 eV which is very close to the reported bandgap of PANI (Abrarov et al. 2005).Figure 8. The photoluminescence spectrum of (a) AZO NPs and(b) PANI film.The optical band gap of AZO film was calculatedbased on the location of the absorption peak. The bandgap for AZO film was 3.2 eV. For AZO films, ions andAl interstitial atoms determines the widening of theband gap caused by increase in carrier concentration.This is the well known Burstein–Moss effect due to theFermi level moving into the conduction band.According to the Burstein–Moss effect, the broadeningof the optical band is a result for doping by Al atoms.Figure 9 displays the graph of (αhν)2 vs.photonenergy hν for the AZO thin film obtained by the supterring method. The linear dependence of (αhν)2 onhν at higher photon energies indicates that AZO film is essentially direct-transition–type semiconducter. Thestraight-line portion of the curve, when extrapolated tozero, gives the optical band gap. From the results ofFigure 9, optical band gap Eopt for AZO thin film is 3.2eV. This band gap is known as the Moss-Burstein shift.Figure 9. Energy band gap determination of AZO sample at roomtemperature.ConclusionsIn this manuscript, we report the fabrication ofaluminum-doped ZnO (AZO) nanoparticle coating onITO glass by using sputtering technique and thesynthesis of PANI on ITO glass by usingelectropolymerization. A new type of organic/inorganichybrid solar cells based on the AZO/PANIheterostructure was developed by sandwiching the twocoated ITO glass plates, and the optoelectric propertiesof devices studied show these heterostructures to bepromising organic/inorganic solar cells devices.Literature CitedAbrarov SM, S Yuldashev, TW Kim, YH Kwon,and TW Kang. 2005. Deep level emission of ZnOnanoparticles deposited inside UV opal. Journalof Luminescence 114:118-124.Amrithesh M, S Aravind, J Jayalekshmi and RSJayasree. 2008. Enhanced luminescence observedin polyaniline –polymethylmethacrylate composite.Journal of Alloys and Compounds 449(1-2):176-179.50010001500200025002 2.5 3 3.5 4Photon Energy (eV)PLIntensity(au)ab0204060801000 1 2 3 4hn (eV)( ahn)2109(cm-1.eV)2Eg = 3.2eV29Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8https://scholarworks.uark.edu/jaas/vol66/iss1/8DOI: https://doi.org/10.54119/jaas.2012.6601S. AbdulAlmohsin, S.M. Al-Mutoki and Z. LiJournal of the Arkansas Academy of Science, Vol. 66, 201230Ansari R and MB Keivani. 2006. Polyanilineconductive electroactive polymers: thermal andenvironmental stability studies. E-Journal ofChemistry 3(4):202-217.Benouis CE, AS Juarez and MS Aida. 2007. Physicsproperties comparison between undoped ZnO andAZO, IZO doped thin films prepared by spraypyrolysis. Journal of Applied Science 7(2):220-225.Catedral MD, AKG Tapia, RV Sarmago, JPTamayo and EJ del Rosario. 2004. Effect ofdopant ions on the electrical conductivity andmicrostructure of polyaniline (emeraldine salt).Science Diliman 16 (2):41-46.Fenske F, W Fuhs, E Nebauer, A Schöpke, B Selleand I Sieber. 1999. Transparent conductive AZOfilms by reactive co-sputtering from separatemetallic Zn and Al Targets. Thin Solid films 343-344:130-133.Gong J, Y Li, Z Hu, Z Zhou and Y Deng. 2010.Ultrasensitive NH3 gas sensor from polyanilineNanograin enchased TiO2 fibers. Journal ofPhysical Chemistry C 144:9970-9974.Gupta SK, A Joshi and M Kaur. 2010. Developmentof gas sensors using ZnO nanostructures. Journalof Chemical Sciences 122(1):57-62.He Y, JA Wang, W Zhang, J Song, C Pei and XChen. 2010. ZnO-nanowire/PANI inorganic/organic hetrostructure light-emitting diode.Journal of Nanoscience Nanotechnology 10:7254-7.Jin AJ and KK Han. 1993. Low resistance and highlyTransparent ITO-Ag-ITO multilayer electrodeusing surface Plasmon resonance of Ag layer bulkhetrojunction organic solar cells. Solar EnergyMaterials and Solar Cells 10:1801-1809.Jung YS, HW Choi and HK Kyung. 2009. Propertiesof AZO thin films for solar cells deposited onpolycarbonate substrates. Journal of the KoreanPhysicals Society 55(5):1945-1949.Kaid MA and A Ashour. 2007. Preparation of AZOfilms by spray pyrolysis technique. AppliedSurface Science 253:3029-3033.Kim JH, DS Park, JH Yu, TS Jeong and CJ Youn.2008. Structural, electrical and optical properties ofepitaxial ZnO layers grown with various O2 flowsby radio-frequency magnetron sputtering. Journalof the Korean Physical Society 52:1818-1822.Kong H, P Yang and J Chu. 2011. Processingparameters and property of AZO thin film preparedby magnetron sputtering. Journal of Physics:Conference Series 276:12170-12174.Lorenz-Hallenberg JI. 2003. Application of poly(3,4-ethylenedioxytheophene)-poly(styrenesulfonate) topoly(vinylidene fluoride) as a Replacement forTraditional Electrodes [M.S. Thesis] MontanaState University, August.Mahmoud WE. 2009. A novel photodiode made ofhybrid Organic/inorganic nano composite. Journalof Physics D: Applied Physics 42:155502-155506.Martinez MJ, C Peng, S Zhang and G Chen. 2008.Electrochemical methods enhance the capacitancein activated carbon/polyaniline composite. Journalof Electrochemical Society 155(10):1-7Moreira LF, MR Lanza, AA Tanka and PSotomayor. 2009. Selective UV-filter detectionwith sensors based on stainless steel electrodesmodified with polyaniline doped with metaltetrasulfonated phthalocyanine films. Analyst134:1453-1461.Rimbu GA, I Stamatin, CL Jackson and K Scott.2006. The morphology control of polyaniline asconducting polymer in fuel cell technology.Journal of Optoelectronics and Advanced Materials8(2):670-674.Sadia A, SG Ansari, M Song, YS Kim and HS Shin.2009. Plasma-enhanced polymerized aniline/TiO2dye sensitized solar cells. Super Lattices andMicrostructures 46:5-9.Shi Y, C Zhang, JH Bechtel, LR Dalton, BRobinson and WH Steier. 2000. Low (sub-1-Volt)half voltage polymeric electro-optic modulatorsachieved by controlling chromophore shape.Science 288:119-122.Sittinger V, F Ruske, W Werner, C Jacobs, BSzyszka and DJ Christie. 2008. High powerpulsed magnetron sputtering of transparentconducting oxides. Thin Solid Films 516:5847-5849.30Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8Published by Arkansas Academy of Science, 2012

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Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar Cells

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 66 Article 82012Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar CellsS. AbdulAlmohsinUniversity of Arkansas at Little Rock, samir_mahdi47@yahoo.comS. M. Al-MutokiTechnical Institute Of ShatrahZ. LiUniversity of Arkansas at Little RockFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Biological and Chemical Physics CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academyof Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu.Recommended CitationAbdulAlmohsin, S.; Al-Mutoki, S. M.; and Li, Z. (2012) "Fabrication and Characterization of Aluminum-doped ZnO/PANI HybridSolar Cells," Journal of the Arkansas Academy of Science: Vol. 66 , Article 8.Available at: http://scholarworks.uark.edu/jaas/vol66/iss1/8Journal of the Arkansas Academy of Science, Vol. 66, 201226Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar CellsS. AbdulAlmohsin1*, S.M. AL-Mutoki2 and Z. Li11Department of Physics, University of Arkansas, Little Rock, AR 72204,USA2Electrical Department, Foundation Of Technical Education, Technical Institute Of Shatrah,Shatrah, ThiQar00964, Iraq*Correspondence: samir_mahdi47@yahoo.comAbstractWe report a facile method to fabricate anAZO/PANI heterostructure by a sandwichingtechnique. Aluminum-doped ZnO (AZO) films weredeposited onto indium tin oxide (ITO) glass using thesputtering technique while PANI films were depositedonto ITO glass using electropolymerization. Theoptoelectric properties of the inorganic/organic devicewere characterized.IntroductionTransparent conductive oxides (TCOs) have a widerange of applications in many fields such as gassensors (Gupta et al. 2010), piezoelectric (Lorenz-Hallenberg 2003), solar cells (Sittinger et al. 2008) andas transparent conductive electrodes (Shi et al. 2000).TCOs have unique properties that combine both hightransparency and high conductivity. In the majority ofsemiconductors, conductivity and transparency arerepulsive and oppose each other. In TCOs, the largeband gap (≈ 3.4 eV) makes them transparent to the region of interest in the solar applications and the non-stoichiometry (lack of oxygen) results in high freecharge concentration and then high conductivity.Indium tin oxide (ITO) is widely and commerciallyused as TCO material, but indium is a scarce elementon Earth, and is toxic. Another drawback of ITO is thatit has low chemical stability. Aluminum-doped zincoxide (AZO) has attracted increasing interest over theyears and has been investigated as an alternative toITO because it exhibits high transmittance (> 90%) andlow resistivity (around 10-4 Ohm.cm) (Jin et al. 1993).AZO is supposed to be less expensive than ITO andalso less toxic. As with any TCO materials, AZO is ann-type semiconductor in nature, with a bandgap around3.4 eV (Jung et al. 2009). AZO films can be preparedby different methods, such as spray pyrolysis (Kaid etal. 2007), and sputtering (Kong et al. 2011). Sputteringis a common way to deposit AZO by using ZnO andAl2O3 targets and sometimes by using two separatetargets of Al and ZnO (Fenske et al. 1999). Recently,AZO nanoparticles (NPs) have attracted increasingattention (Benouis et al. 2007) as a result of the rapiddevelopment of nanotechnology and nanomaterials.One of the promising applications of AZO NPs is theproduction of efficient solar converters because theNPs films introduce a large junction area in solar cells.Polyaniline (PANI) is one of the best, facile andconductive polymers (Rimbu et al. 2006) with feasiblestability against the environment (Ansari et al. 2006).Its conductivity arises from the -electron conjugate inthe polymeric chain. PANI is naturally a p-typematerial with an optical band gap of about 3 eV. As apolymer, the energy gap diagram of PANI is notcomprised of conduction and valence bands, but ratherit is described by the highest occupied molecularorbital (HOMO) and the lowest unoccupied molecularorbital (LUMO). The HOMO level of PANI is 7.7 eV,while the LOMO level is 4.7 eV. (Catedral et al. 2004).PANI can be synthesized by different techniques, suchas plasma enhanced polymerization (Sadia et al. 2009)and electrochemical techniques (Martinez et al. 2008).Recently, hybrid inorganic/organic heterojunctiondevices have received much attention as promisingjunctions for many applications, such as gas sensors(Gong et al. 2010), light emitting diodes (He et al.2010), and photo detectors (Mahmoud 2009).ZnO/PANI has gained a lot of interest for itsluminescence properties (Amrithesh et al. 2009) andUV detection (Moreira et al. 2009). In this paper,AZO/PANI heterostructure sandwiched between twoITO-coated glass was studied. AZO films weredeposited using the sputtering technique while PANIfilms were deposited using by electro polymerization.The AZO films in solar cells are used as a windowlayer and an active material.MethodsAniline monomer was distilled twice underreduced pressure before use, and dissolved into a 1 Msulfuric acid to make a 0.1 M solution. The polyanilinewas synthesized with a galvanostatic step method at aconstant voltage of 3 V. The working electrode was a26Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8Published by Arkansas Academy of Science, 2012commercial ITOpaper clipofweighing the working electrodeelectro depositiondiagrampolymerizationwiththe range 24 mto 0.076impuritywas kept at0.101 AtimeFigureprepare the PANIsandwiching themensurePANI,electrochemical process when the PANI was still wetA schematic diagramillustrated in Figurecharacunder illumination usingIrradiation was achieved from the TiOthe nanoFiguretheThe AZO filmsputtering poweof1AZO2electrodeposited polyawas used an anode.,40 min. Schematicintimate contact between thethe two films were sandwiched right after theteristics have been investigated in the dark andc. A schematic diagram of theFabrication andwasof the electrochemical cellml/minandfilm and PANIomposite side.used as.torr180vo.thin film.-glass.~.oCltagediagramFigure 1was sputteredr of 150 W30 mAn ZnO disk, theto create2witha counter electrode.ofof the electrochemical cell used toof. Current densityanITOPANIJournal of the Arkansas Academy of Science, Vol. 66, 2012atorrcurrent261 to 202werethe fabricated device isAM1.5 sunlight simulator.ITOAZOCharacterization of Asurface area ofniline was estimated bywithThebrought into contacttheAZObefdisplaysundersubstrate temperaturewas set at-ore and afterontoa flow ratewith 2 wt% AlVheterostructure. ToPANIthe ITO glassAr pressure, with aAZO-voltage2 side and fromheterostructure1.5The amounta schematicfor in situof 0.0750.097 toand thecmsputter(Jluminum2. Athein2O3by.-V).27ResultsAZO NPs using the scanning electron microscopy(SEM).to 100 nm. The film displays a good uniformity withlittle agglomeration.Figure 3. SEM photheterodiodebehavior with a rectification of 28 atstands for the ratio of the forward to reverse current ataindicates the formation of a diode between AZO nfilm and PANI pdiode illustrates a gradual increabreakdiode.behavior of the form:wq/kT is the thermal energy and n is the ideality factor.Figurdevice. The curve exhibits a linear behavior in the biasregion of 0.05diode is:current ofcalculated from this equation is 4.3.ndomina-dopedFigure 3 demonstrates the surface topography ofThe dcertain bias voltage).hereThe equationsuggest-downIeZand DiscussionThe diameter of AZO NPs ranges from 50 nmark JThe fo is the saturation current, V is the bias voltage,5 represents the semistednO/PANI Hybridshown in Figure, which is a feature of the hete4 ×that the carrier transport of this device isby more thao of AZO NPs deposited onto ITO glass.-V characteristics of the AZO/PANI-orward current showsI-0.3 V. The empirical equation of thisI10type film. The reverse current of this0indicate-5 A, while the ideality factor that isexpIo00004.ns an extrapolated saturatone mechanism.The rnkTqVexpSolar Cells4-log Iexhibitectifying behaviorse,87.8±1 V (rectificationreferring to a softan exponential,-V curve of theVThe high value ofa rectifyingrojunction-type(1)(2)ion27Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8http://scholarworks.uark.edu/jaas/vol66/iss1/8S. AbdulAlmohsin, S.M. Al-Mutoki and Z. LiJournal of the Arkansas Academy of Science, Vol. 66, 2012280.000010.00010.0010.010 0.1 0.2 0.3 0.4Bias Voltage (V)ForwardCurrent(A)Figure 4. Dark I-V characteristics of AZO/PANI heterojunction, y-axis multiply by 10-2.Figure 5. The semi-log I-V plot at the forward bias, Y-Axesmultiply by 10-2.The J-V characteristics of the AZO/PANI thin filmsolar cell exhibit considerable photovoltaicperformance under illumination AM 1.5 (~100mW/cm2), as depicted in Fig. 6, with a short circuitcurrent density (ISC) of 0.075 mA/cm2, an open circuitvoltage (VOC) of 195 V and a fill-factor (FF) of 0.41.The photon conversion efficiency (PCE) of the cell is0.0078%, which indicates a significant performance.The photovoltaic performances of the AZO/PANIdevices under different illumination intensities arelisted in Table 1.The use of the sandwiching technique to fabricate aheterojunction has not been reported in the literature todate and most of the existing papers use the subsequentdeposition of the two layers. The rectification behavior-0.4 -0.2 0.0 0.2 0.4 0.6-0.24-0.120.000.120.24Current(mA/cm2 )Voltage(V)ZNO doped ALLight And DarkFigure 6. The J-V characteristics under AM1.5 illumination.and the acceptable photovoltaic performance of thedevice presented above suggest a successful formationof a heterojunction between AZO nanoparticles andPANI, indicating that the sandwiching technique isuseful in the fabrication of this kind of heterojunction.The wet surface of PANI directly after theelectropolymerization helps to form an intimate contactwith AZO nanoparticle film, and the morphology of thebumpy AZO surface could help to increase the junctionarea. An SEM photographs. In the subsequentdeposition, the AZO nanoparticle film needs to be usedas a working electrode. That can cause a degradation ofthe AZO film when it is immersed in the electrolyteand, in addition, the AZO film may dissolve in theelectrolyte because of the effect of the sulfuric acid.Furthermore, the subsequent deposition needs to makeohmic contact onto the PANI surface, requiring the useof the evaporation technique to deposit the metal ontothe PANI surface, which could degrade the PANIperformance.Table 1. The photovoltaic performances of theAZO/PANI devices under different illuminationintensities.Illumination(mW/cm2)WIsc(mA/cm2)Voc(volt)FF PCE(%)100 0.075 0.195 0.41 6.0 ×10-380 0.055 0.18 0.57 7.1 × 10-350 0.04 0.15 0.63 7.6 ×10 -325 0.025 0.15 0.61 9.1 × 10-3The room temperature photoluminescence (PL) ofAZO nanoparticles deposited onto ITO glass is shown-10-8-6-4-20246810-1.5 -0.5 0.5 1.5Bias Voltage (V)DarkCurrent(mA)28Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8Published by Arkansas Academy of Science, 2012Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar CellsJournal of the Arkansas Academy of Science, Vol. 66, 20122910001050110011501200125013002 2.5 3 3.5 4Photon Energy (eV)PLIntensity(au)in Figure 8. The PL spectrum shows a near-band-edgeat 3.46 eV, which represents the direct band gap ofAZO. The deep-level emission appears at 2.27 eV,which represents the defects inside the AZOnanoparticles. The intensity ratio (Inear-band/Ideep-level) isabout 1.8, indicating a very high quality film with highcrystallinity and is higher than previously reportedresults (Kim et al. 2008). The PANI film shows a PLpeak of 2.9 eV which is very close to the reported bandgap of PANI (Abrarov et al. 2005).Figure 8. The photoluminescence spectrum of (a) AZO NPs and(b) PANI film.The optical band gap of AZO film was calculatedbased on the location of the absorption peak. The bandgap for AZO film was 3.2 eV. For AZO films, ions andAl interstitial atoms determines the widening of theband gap caused by increase in carrier concentration.This is the well known Burstein–Moss effect due to theFermi level moving into the conduction band.According to the Burstein–Moss effect, the broadeningof the optical band is a result for doping by Al atoms.Figure 9 displays the graph of (αhν)2 vs.photonenergy hν for the AZO thin film obtained by the supterring method. The linear dependence of (αhν)2 onhν at higher photon energies indicates that AZO film is essentially direct-transition–type semiconducter. Thestraight-line portion of the curve, when extrapolated tozero, gives the optical band gap. From the results ofFigure 9, optical band gap Eopt for AZO thin film is 3.2eV. This band gap is known as the Moss-Burstein shift.Figure 9. Energy band gap determination of AZO sample at roomtemperature.ConclusionsIn this manuscript, we report the fabrication ofaluminum-doped ZnO (AZO) nanoparticle coating onITO glass by using sputtering technique and thesynthesis of PANI on ITO glass by usingelectropolymerization. A new type of organic/inorganichybrid solar cells based on the AZO/PANIheterostructure was developed by sandwiching the twocoated ITO glass plates, and the optoelectric propertiesof devices studied show these heterostructures to bepromising organic/inorganic solar cells devices.Literature CitedAbrarov SM, S Yuldashev, TW Kim, YH Kwon,and TW Kang. 2005. Deep level emission of ZnOnanoparticles deposited inside UV opal. Journalof Luminescence 114:118-124.Amrithesh M, S Aravind, J Jayalekshmi and RSJayasree. 2008. Enhanced luminescence observedin polyaniline –polymethylmethacrylate composite.Journal of Alloys and Compounds 449(1-2):176-179.50010001500200025002 2.5 3 3.5 4Photon Energy (eV)PLIntensity(au)ab0204060801000 1 2 3 4hn (eV)( ah n)2109(cm-1.eV)2Eg = 3.2eV29Journal of the Arkansas Academy of Science, Vol. 66 [2012], Art. 8http://scholarworks.uark.edu/jaas/vol66/iss1/8S. AbdulAlmohsin, S.M. Al-Mutoki and Z. 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Fabrication and Characterization of Aluminum-doped ZnO/PANI Hybrid Solar Cells

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