Browsing by Subject "Solar cells"
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Item Open Access Amyloid-like peptide nanofiber templated titania nanostructures as dye sensitized solar cell anodic materials(Royal Society of Chemistry, 2013) Acar, H.; Garifullin, R.; Aygun, L. E.; Okyay, Ali Kemal; Güler, Mustafa O.One-dimensional titania nanostructures can serve as a support for light absorbing molecules and result in an improvement in the short circuit current (Jsc) and open circuit voltage (Voc) as a nanostructured and high-surface-area material in dye-sensitized solar cells. Here, self-assembled amyloid-like peptide nanofibers were exploited as an organic template for the growth of one-dimensional titania nanostructures. Nanostructured titania layers were utilized as anodic materials in dye sensitized solar cells (DSSCs). The photovoltaic performance of the DSSC devices was assessed and an enhancement in the overall cell performance compared to unstructured titania was observed.Item Open Access Anatase TiO2 nanowires functionalized by organic sensitizers for solar cells: a screened Coulomb hybrid density functional study(American Institute of Physics Inc., 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtıoğlu, S.; Mete, E.The adsorption of two different organic molecules cyanidin glucoside (C21O11H20) and TA-St-CA on anatase (101) and (001) nanowires has been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye-nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the states inside the conduction band. The wide-bandgap anatase nanowires can be functionalized for solar cells through electron-hole generation and subsequent charge injection by these dye sensitizers. The intermolecular charge transfer character of Donor-π-Acceptor type dye TA-St-CA is substantially modified by its adsorption on TiO2 surfaces. Cyanidin glucoside exhibits relatively stronger anchoring on the nanowires through its hydroxyl groups. The atomic structures of dye-nanowire systems re-optimized with the inclusion of nonlinear solvation effects showed that the binding strengths of both dyes remain moderate even in ionic solutions.Item Open Access A baseball-bat-like CdTe/TiO2 nanorods-based heterojunction core–shell solar cell(Elsevier, 2013) Karaagac, H.; Parlak, M.; Aygun, L. E.; Ghaffari, M.; Bıyıklı, Necmi; Okyay, Ali KemalRutile TiO2 nanorods on fluorine-doped thin oxide glass substrates via the hydrothermal technique were synthesized and decorated with a sputtered CdTe layer to fabricate a core-shell type n-TiO2/p-CdTe solar cell. Absorbance spectrum verified the absorption contribution of both TiO2 and CdTe to the absorption process. The solar cell parameters, such as open circuit voltage, short circuit current density, fill factor and power conversion efficiency were found to be 0.34 V, 1.27 mA cm-2, 28% and 0.12%, respectively. .Item Open Access Comparative study of thin film n-i-p a-Si: H solar cells to investigate the effect of absorber layer thickness on the plasmonic enhancement using gold nanoparticles(Elsevier Ltd, 2015) Islam, K.; Chowdhury F.I.; Okyay, Ali Kemal; Nayfeh, A.In this paper, the effect of gold nanoparticles on n-i-p a-Si:H solar cells with different intrinsic layer (i-layer) thicknesses has been studied. 100nm and 500nm i-layer based n-i-p a-Si:H solar cells were fabricated and colloidal gold (Au) nanoparticles dispersed in water-based solution were spin-coated on the top surface of the solar cells. The Au nanoparticles are of spherical shape and have 100nm diameter. Electrical and quantum efficiency measurements were carried out and the results show an increase in short-circuit current density (Jsc), efficiency and external quantum efficiency (EQE) with the incorporation of the nanoparticles on both cells. Jsc increases from 5.91mA/cm2 to 6.5mA/cm2 (~10% relative increase) and efficiency increases from 3.38% to 3.97% (~17.5% relative increase) for the 100nm i-layer solar cell after plasmonic enhancement whereas Jsc increases from 9.34mA/cm2 to 10.1mA/cm2 (~7.5% relative increase) and efficiency increases from 4.27% to 4.99% (~16.9% relative increase) for the 500nm i-layer cell. The results show that plasmonic enhancement is more effective in 100nm than 500nm i-layer thickness for a-Si:H solar cells. Moreover, the results are discussed in terms of light absorption and electron hole pair generation. © 2015 Elsevier Ltd.Item Open Access Complexing agent effect on the stoichiometric ratio of the electrochemically prepared CuInSe2 thin films(Elsevier, 2007) Beyhan, S.; Süzer, Şefik; Kadırgan, F.The electrodeposition of CuInSe2 is investigated to improve the stoichiometric properties of CuInSe2 layers on indium tin oxide (ITO)-coated glass substrates and to develop one-step electrodeposition method for solar cell applications. XPS was utilized for the characterization of the surface properties of CuInSe2 layers. The influence of the complexing agent, e.g. benzotriazole, bulk concentration of Cu and Se and deposition potentials on the stoichiometric properties, are discussed. © 2007 Elsevier B.V. All rights reserved.Item Open Access Effect of gold nanoparticles size on light scattering for thin film amorphous-silicon solar cells(Elsevier Ltd, 2014-05) Islam, K.; Alnuaimi, A.; Battal, E.; Okyay, Ali Kemal; Nayfeh, A.In this work, the effect of gold (Au) nanoparticles on the performance of a-Si:H solar cells is investigated experimentally. The solar cell stack is grown on a highly doped p-type Si wafer and consists of 20nm heavily doped p-type a-Si, 500nm undoped a-Si, 20nm heavily doped n-type a-Si and finally 80nm Indium Tin Oxide (ITO) on the top. Au nanoparticles of 10, 20, 50, 80, 100, 200 and 400nm are spin coated on top of the ITO before metallization. The plasmonic effect of the Au nanoparticles allows for additional scattering at the surface thus reducing the overall reflectivity. The larger the nanoparticle size the more scattering is obtained and the median reflectivity drops from about 23% to 18%. The results show an increase in the short-circuit current density (Jsc) and efficiency with increasing nanoparticle size. The Jsc increases from 9.34 to 10.1mA/cm2. In addition, the efficiency increases from 4.28% to 5.01%. © 2014 Elsevier Ltd.Item Open Access Electron spectroscopic investigations of CdS and CdTe electrochemically coated on glass(Springer, 1996) Süzer, Ş.; Kutun, Ş.; Kadırgan, F.The electrodeposition of CdS and CdTe is investigated to improve the stoichiometric properties of CdS/CdTe layers on ITO-glass substrates for solar cell applications. X-ray photoelectron spectroscopy is utilized for the characterization of the CdS and CdTe layers. The influence of the electrodeposition potential, the pH and the thiosulfate concentration on the stoichiometry of CdS and CdTe layers are discussed. © Springer-Verlag 1996.Item Open Access Enhanced light scattering with energy downshifting using 16 nm indium nitride nanoparticles for improved thin-film a-Si N-i-P solar cells(Electrochemical Society Inc., 2015-05) Chowdhury F.I.; İslam, K.; Alkış, Sabri; Ortaç, Bülend; Alevli, Mustafa; Dietz, N.; Okyay, Ali Kemal; Nayfeh, A.In this work the effect of Indium nitride (InN) nanoparticles (NPs) on the performance of a-Si: H solar cells has been investigated. The average Jsc of InN NPs coated cells was found 6.76 mA/cm2 which is 16.69% higher than the average Jsc of the reference cell which was 5.79 mA/cm2. Average efficiency of InN NPs coated cells showed 14.16% increase from 3.32% to 3.79%. Peak EQE has increased from 44.8% at 500 nm to 51.67% at 510 nm and peak IQE has increased from 51.70% at 510 nm to 68.38% at 500 nm for InN NPs coated cell. Further study shows that EQE change is larger between 510 nm-700 nm compared to IQE change indicting a surface scattering mechanism that reduces the reflectivity. However, between 400 nm-510 nm IQE change is larger than EQE change which indicates that energy downshifting mechanism is dominating. So overall performance enhancement can be attributed to the scattering and photoluminescence properties of InN NPs that enhances absorption inside a-Si: H solar cells. © The Electrochemical Society.Item Open Access Examination of the temperature related structural defects of InGaN/GaN solar cells(Academic Press, 2015) Durukan, İ. K.; Bayal, Ö.; Kurtuluş, G.; Baş, Y.; Gültekin, A.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Özçelik, S.; Özbay, EkmelIn this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 °C. The defect density increased on the GaN layer starting from 350 °C and reaching above 400 °C. A similar trend is observed on the InGaN layer, too.Item Open Access Improved efficiency of thin film a-Si:H solar cells with Au nanoparticles(Institute of Electrical and Electronics Engineers Inc., 2013) Islam, K.; Alnuaimi, A.; Okyay, Ali Kemal; Nayfeh, A.In this work, the effect of Au nanoparticles on the performance of a-Si:H solar cells is investigated experimentally. Au nanoparticles of 10, 20, 50, 80, 100, 200 and 400 nm are spin coated on ITO before metallization. The results show an increase in the Jsc and efficiency with increasing nanoparticle size. The Jsc increases from 9.34 mA/cm2 to 10.1 mA/cm2. In addition, the efficiency increases from 4.28% to 5.01%. © 2013 IEEE.Item Open Access Improving the efficiency enhancement of photonic crystal based InGaN solar cell by using a GaN Cap Layer(Hindawi Publishing Corporation, 2014) Gundogdu, T.F.; Gökkavas, M.; Özbay, EkmelWe studied a high indium content (0.8) InGaN based solar cell design where the active InGaN layer is sandwiched between a GaN cap layer and a GaN spacer layer. The incorporation of the sacrificial cap layer allows for the etching of the front surface without removing the active InGaN resulting in a 50% enhancement of the short-circuit current density for a 15 nm-thick InGaN layer. © 2014 T. F. Gundogdu et al.Item Open Access Indium rich InGaN solar cells grown by MOCVD(Springer New York LLC, 2014) Çakmak, H.; Arslan, E.; Rudziński, M.; Demirel, P.; Unalan, H. E.; Strupiński, W.; Turan, R.; Öztürk, M.; Özbay, EkmelThis study focuses on both epitaxial growths of InxGa 1-xN epilayers with graded In content, and the performance of solar cells structures grown on sapphire substrate by using metal organic chemical vapor deposition. The high resolution X-ray and Hall Effect characterization were carried out after epitaxial InGaN solar cell structures growth. The In content of the graded InGaN layer was calculated from the X-ray reciprocal space mapping measurements. Indium contents of the graded InGaN epilayers change from 8.8 to 7.1 % in Sample A, 15.7-7.1 % in Sample B, and 26.6-15.1 % in Sample C. The current voltage measurements of the solar cell devices were carried out after a standard micro fabrication procedure. Sample B exhibits better performance with a short-circuit current density of 6 mA/cm2, open-circuit voltage of 0.25 V, fill factor of 39.13 %, and the best efficiency measured under a standard solar simulator with one-sun air mass 1.5 global light sources (100 mW/cm2) at room temperature for finished devices was 0.66 %.Item Open Access Influence of gold-silica nanoparticles on the performance of small-molecule bulk heterojunction solar cells(Elsevier BV * North-Holland, 2015) Xu, X.; Kyaw, A. K. K.; Peng, B.; Xiong, Q.; Demir, Hilmi Volkan; Wang Y.; Wong, T. K. S.; Sun, X. W.Light trapping by gold (Au)-silica nanospheres and nanorods embedded in the active layer of small-molecule (SM) organic solar cell has been systematically compared. Nanorod significantly outperforms nanosphere because of more light scattering and higher quality factor for localized surface plasmon resonance (LSPR) triggered by nanorods. The optimum concentration of nanorod was characterized by charge carrier transport and morphology of the active layers. At optimum nanorod concentration, almost no change in the morphology of the active layer reveals that LSPR and scattering effects rather than the morphology are mainly responsible for the enhanced power conversion efficiency. In addition, the preliminary lifetime studies of the SM solar cells with and without Au-silica nanorods were conducted by measuring the current density-voltage characteristics over 20 days. The results show that plasmonic device with nanorods has no adverse impact on the device stabilityItem Open Access Lithium salt-nonionic surfactant lyotropic liquid crystalline gel-electrolytes with redox couple for dye sensitized solar cells(Royal Society of Chemistry, 2016) Yılmaz, E.; Olutaş, E. B.; Barım, G.; Bandara, J.; Dag, Ö.Lithium salt (LiCl, LiBr, LiI, or LiNO3) and a non-ionic surfactant (such as 10-lauryl ether, C12E10) form lyotropic liquid crystalline (LLC) mesophases in the presence of a small amount of water. The mesophases can be prepared as gels by mixing all the ingredients in one pot or in the solution phase that they can be prepared by coating over any substrate where the LLC phase is formed by evaporating excess solvent. The second method is easier and produces the same mesophase as the first method. A typical composition of the LLC phases consists of 2-3 water per salt species depending on the counter anion. The LiI-C12E10 mesophases can also be prepared by adding I2 to the media to introduce an I-/I3 - redox couple that may be used as a gel-electrolyte in a dye-sensitized solar cell. Even though the mesophases contain a large amount of water in the media, this does not affect the cell performance. The water molecules in the mesophase are in the hydration sphere of the ions and do not act like bulk water, which is harmful to the anode of the dye-sensitized solar cells (DSSC). There are two major drawbacks of the salt-surfactant LLC mesophases in the DSSCs; one is the diffusion of the gels into the pores of the anode electrode and the other is the low ionic conductivity. The first issue was partially overcome by introducing the gel content as a solution and the gelation was carried in/over the pores of the dye modified titania films. To increase the ionic conductivity of the gels, other salts (such as LiCl, LiBr, and LiNO3) with better ionic conductivity were added to the media, however, those gels behave less effectively than pure LiI/I2 systems. Overall, the DSSCs constructed using the LLC electrolyte display high short circuit current (Isc of around 10 mA), high open circuit voltage (Voc of 0.81 V) and good fill factor (0.69) and good efficiency (3.3%). There is still room for improvement in addressing the above issues in order to enhance the cell efficiency by developing new methods of introducing the gel-electrolytes into the mesopores of the anode electrode.Item Open Access Nanosecond pulsed laser ablated sub-10 nm silicon nanoparticles for improving photovoltaic conversion efficiency of commercial solar cells(Institute of Physics Publishing Ltd., 2017) Rasouli, H. R.; Ghobadi, A.; Ghobadi, T. G. U.; Ates, H.; Topalli, K.; Okyay, Ali KemalIn this paper, we demonstrate the enhancement of photovoltaic (PV) solar cell efficiency using luminescent silicon nanoparticles (Si-NPs). Sub-10 nm Si-NPs are synthesized via pulsed laser ablation technique. These ultra-small Si nanoparticles exhibit photoluminescence (PL) character tics at 425 and 517 nm upon excitation by ultra-violet (UV) light. Therefore, they can act as secondary light sources that convert high energetic photons to ones at visible range. This down-shifting property can be a promising approach to enhance PV performance of the solar cell, regardless of its type. As proof-of-concept, polycrystalline commercial solar cells with an efficiency of ca 10% are coated with these luminescent Si-NPs. The nanoparticle-decorated solar cells exhibit up to 1.64% increase in the external quantum efficiency with respect to the uncoated reference cells. According to spectral photo-responsivity characterizations, the efficiency enhancement is stronger in wavelengths below 550 nm. As expected, this is attributed to down-shifting via Si-NPs, which is verified by their PL characteristics. The results presented here can serve as a beacon for future performance enhanced devices in a wide range of applications based on Si-NPs including PVs and LED applications.Item Open Access Nanosphere concentrated photovoltaics with shape control(Wiley, 2020-12) Esmaeilzad, N. S.; Demir, Ahmet Kemal; Hajivand, J.; Çiftpınar, H.; Turan, R.; Kurt, H.; Bek, A.Dielectric colloidal nanospheres (NSs) are promising candidates for light management in photonic devices such as solar cells (SCs). NS arrays can direct the broad incident solar radiation into a set of tighter foci, at which light intensity becomes considerably concentrated, enabling higher photovoltaic conversion efficiency. Furthermore, the NS arrays acting as an effective medium on the SC surface can reduce reflectance and facilitate improved forward scattering. Therefore, uniform arrays of NSs located on top of the SC can behave as antireflection coatings or as microlenses, which can be regarded as a surface distributed light concentrator within the framework of concentrated photovoltaics. Fabrication of NS‐based light‐trapping structures is low‐cost and less complicated than common alternatives such as vacuum evaporated multilayer antireflection coatings. In this work, experimental demonstration and computational confirmation on the shape adjustment of such NS structures for improved light harvesting and efficiency enhancement in Si SCs are studied. The light conversion efficiency of Si solar cells is shown to improve by more than 27% with shape adjustment of NS arrays.Item Unknown Nonradiative resonance energy transfer directed from colloidal CdSe/ZnS quantum dots to epitaxial InGaN/GaN quantum wells for solar cells(Wiley, 2010-06-04) Nizamoglu, S.; Sari, E.; Baek, J. H.; Lee, I. H.; Demir, Hilmi VolkanWe report on Förster-type nonradiative resonance energy transfer (NRET) directed from colloidal quantum dots (QDs) to epitaxial quantum wells (QWs) with an efficiency of 69.6% at a rate of 1.527 ns-1 for potential application in III-nitride based photovoltaics. This hybrid exciton generation-collection system consists of chemically-synthesized cyan CdSe/ZnS core/shell QDs (λPL = 490 nm) intimately integrated on epitaxially-grown green InGaN/GaN QWs (λPL = 512 nm). To demonstrate directional NRET from donor QDs to acceptor QWs, we simultaneously show the decreased photoluminescence decay lifetime of dots and increased lifetime of wells in the hybrid dipole-dipole coupled system.Item Unknown Observation of biexcitons in the presence of trions generated via sequential absorption of multiple photons in colloidal quantum dot solids(IEEE, 2012) Cihan, Ahmet Fatih; Hernandez-Martinez Pedro L.; Kelestemur, Yusuf; Demir, Hilmi VolkanMulti exciton generation (MEG) and multi exciton recombination (MER) in semiconductor quantum dots (QDs) have recently attracted significant scientific interest as a possible means to improve device efficiencies [1-5]. Convenient bandgap tunability, easy colloidal synthesis, and solution-based processability of these QDs make them further attractive for such device applications using MEG and MER. For example, recent theoretical and experimental studies have shown that MEG enables >100% peak external quantum efficiency where the generated multi excitons (MEs) are collected in a simple QD solar cell structure [1]. Furthermore, MEG has also been shown in QD photodetectors exhibiting substantially increased photocurrent levels [2]. Another promising application for MEs is the use of QDs as an alternative gain medium based on MER for lasers. Although MEG is very promising and supported with quite persuasive reports, there are still some debatable issues that need to be clarified. One of the issues that have generated great debates in the field has been the confusion of MER with the recombination of trions, which takes place in photocharged QDs. To utilize MEG and MER in practical devices such as QD solar cells and QD lasing devices, these phenomena need to be well understood. Here, we showed distinct spectrally-resolved temporal behavior of biexciton (BX), single exciton (X) and trion radiative recombinations in near unity quantum yield (QY) quasi-type II CdSe/CdS core/shell nanocrystal QDs. Upon sequential absorption of multiple photons, the extraction of Xs, BXs, and trions were achieved using time correlated single photon counting (TCSPC) measurements performed on low concentration thin film samples of these QDs at different emission wavelengths. The QDs were embedded in PMMA medium to obtain homogeneous samples and avoid Förster-type nonradiative energy transfer (NRET) between them. Here to extract Xs, BXs, and trions, we devised a new analysis approach for the time decays of the QDs that allowed us to attribute the physical events to their corresponding time decay terms, which were further verified with their excitation intensity dependencies [6]. © 2012 IEEE.Item Unknown Optimization of distyryl-Bodipy chromophores for efficient panchromatic sensitization in dye sensitized solar cells(2011) Kolemen, S.; Cakmak, Y.; Ertem, E.; Bozdemir, O. A.; Erten-Ela, S.; Marszalek, M.; Yum, Jun-Ho; Zakeeruddin, S.; Nazeeruddin, M.; Gratzel, M.; Akkaya, E. U.Versatility of Bodipy (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes was further expanded in recent dye-sensitized solar cell applications. Here we report a series of derivatives designed to address earlier problems in Bodipy sensitized solar cells. In the best case example, an overall efficiency of a modest 2.46% was achieved, but panchromatic nature of the dyes is quite impressive. This is the best reported efficiency in liquid electrolyte solar cells with Bodipy dyes as photosensitizers.Item Unknown Photonic metamaterial absorber designs for infrared solar-cell applications(SPIE, 2010) Alıcı, Kamil Boratay; Özbay, EkmelWe propose a metamaterial based absorber design that operates at the infrared regime. The absorption peak was 83.6%. We can incorporate solar-cell layers inside the metamaterial absorber in order to significantly increase solar-cell efficiency. © 2010 SPIE.