Browsing by Subject "Photovoltaics"

Now showing 1 - 15 of 15

Open Access
Chemically specific dynamic characterization of photovoltaic and photoconductivity effects of surface nanostructures
(American Chemical Society, 2010) Ekiz, O. Ö.; Mizrak, K.; Dâna, A.
We report characterization of photovoltaic and photoconductivity effects on nanostructured surfaces through light induced changes in the X-ray photoelectron spectra (XPS). The technique combines the chemical specificity of XPS and the power of surface photovoltage spectroscopy (SPV), with the addition of the ability to characterize photoconductivity under both static and dynamic optical excitation. A theoretical model that quantitatively describes the features of the observed spectra is presented. We demonstrate the applicability of the model on a multitude of sample systems, including homo- and heterojunction solar cells, CdS nanoparticles on metallic or semiconducting substrates, and carbon nanotube films on silicon substrates.
Open Access
Communication: Enhancement of dopant dependent x-ray photoelectron spectroscopy peak shifts of Si by surface photovoltage
(2011) Sezen, H.; Süzer, Şefik
Binding energies measured by x-ray photoelectron spectroscopy (XPS) are influenced by doping, since electrons are transferred to (p-type) and from (n-type) samples when they are introduced into the spectrometer, or brought into contact with each other (p-n junction). We show that the barely measurable Si2p binding energy difference between moderately doped n- and p-Si samples can be enhanced by photoillumination, due to reduction in surface band-bending, which otherwise screens this difference. Similar effects are also measured for samples containing oxide layers, since the band-bending at the buried oxide-Si interfaces is manifest as photovoltage shifts, although XPS does not probe the interface directly. The corresponding shift for the oxide layer of the p-Si is almost twice that of without the oxide, whereas no measurable shifts are observable for the oxide of the n-Si. These results are all related to band-bending effects and are vital in design and performance of photovoltaics and other related systems.
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.
Open Access
Development of photoanodes for performance enhanced dye sensitized solar cells
(2015-08) Ulusoy, Türkan Gamze
With a raising demand for clean and renewable energy sources in recent decades, dye sensitized solar cell (DSSC), as an efficient and low-cost solar cell technology, have attracted considerable attention and several efforts have been directed for the optimization of all components of DSSCs including photoanode, sensitizer dye, hole transport layer and counter electrode. The objective of this thesis is to provide a better understanding on the function of photoanode in overall performance of DSSC device by highlighting problems and limitations and offering proper solutions to tackle these deficiencies. Based on this understanding, this thesis reports, fabrication, characterization and analysis of designed three different cells to boost device photovoltaic performance which includes: 1) angstrom thick ZnO-sheathed TiO2 nanowires as photoanodes, 2) multifunctional omnidirectional antireflective coating, 3) peptide nanofiber network templated ALD-grown TiO2 nanostructures as photoanodes in DSSC. Since photoanode-dye interface engineering is of utmost importance, the first of our proposals in this thesis relies on a systematic approach to understand the impact of atomic layer deposited (ALD) angstrom-thick ZnO sheath on hydrothermally grown TiO2 nanowires (NWs) core utilized as photoanodes in DSSC. The results show that this ultrathin layer will contribute at device efficiency enhancement almost three times via reducing recombination rate of injected electrons, enhancement in collection efficiency of electrons via reducing density of surface trap states without hampering injection efficiency and increased dye uptake on TiO2 nanowires’ surface which in turn leads to increased light absorption. On the other work, we also utilized multifunctional organically modified silica (ORMOSIL) as antireflection coating layer on DSSC to improve conversion efficiency of the device via reduction in the light reflection. ORMOSIL coated DSSC surfaces show a low-reflective omnidirectional response in a wide range of wavelengths (400-800 nm). At normal incidence (𝜃=0°), the short circuit current density (JSC) is improved to an amount of 23% as a result of ORMOSIL coating. In addition, JSC meets even higher amounts of enhancement where 84% increase is recorded at 𝜃=30°. Moreover, this coating exhibits superhydrophobicity representing a contact angle of 155º. Finally, we proposed and implemented, self-assembled peptide amphiphiles nanofiber 3D networks in order to obtain TiO2 nanotube structures as a template in DSSC. These self-assembled peptide amphiphiles are resistant to high temperature and more durable than other kinds of peptide amphiphiles. The advantage of this 3D fiber composed template is its high surface area and interconnected solid support providing an effective template for formation of TiO2 network using ALD. On the other hand, since ALD offers uniform and conformal coating of high aspect ratio features, it ensures an ideal thin film coating method on high surface area nano-template materials such as the peptide nanofiber templates proposed in this study.
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.
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.
Open Access
Novel volumetric plasmonic resonator architectures for enhanced absorption in thin-film organic solar cells
(2010) Sefünç, Mustafa Akın
There has been a growing interest in decreasing the cost and/or increasing the efficiency of clean renewable energy resources including those of photovoltaic approaches for conversion of sunlight into electricity. Today, although photovoltaics is considered a potential candidate in diversification of energy sources, the cost of photovoltaic systems remains yet to be reduced by several factors to compete with fossil fuel based energy production. To this end, new generation solar cells are designed to feature very thin layers of active (absorbing) materials in the order of tens of nanometers. Though this approach may possibly decrease the cost of solar cells, these ultra-thin absorbing layers suffer from undesirably low optical absorption of incident photons. Recently revolutionary efforts on increasing light trapping using nanopatterned metal layers in the active photovoltaic material via surface plasmon excitations have been demonstrated, which attracted interest of the academic community as well as the industry. In these prior studies, plasmonic structures, placed either on the top or at the bottom of absorbing layers, have been investigated to enhance the absorption in the active material. However, all these previous efforts were based only on using a single layer of plasmonic structures. In this thesis, different than the previous reports of our group and the others, we focus on a new design concept of volumetric plasmonic resonators that relies on the idea of incorporating two (or more) layers of coupled plasmonic structures embedded in the organic solar cells. For proof-of-concept demonstration, here we embody one silver grating on the top of the absorbing layer and another at the bottom of the active layer to couple them with each other such that the resulting field localization is further increased and extended within the volume of the active material. In addition to individual plasmonic resonances of these metallic structures, this allows us to take the advantage of the vertical interaction in the volumetric resonator. Our computational results show that this architecture exhibits a substantial absorption enhancement performance particularly under the transverse-magnetic polarized illumination, while the optical absorption is maintained at a similar level as the top grating alone under the transverseelectric polarized illumination. As a result, the optical absorption in the active layer is enhanced up to ~67%, surpassing the improvement limit of individual gratings, when the total film thickness is kept fixed. This volumetric interaction contributes to further enhancement of optical absorption in the active layer, beyond the limited photon absorption in non-metallic (bare) organic solar cell.
Open Access
Optically thin composite resonant absorber at the near-infrared band: A polarization independent and spectrally broadband configuration
(Optical Society of American (OSA), 2011) Boratay Alici, K.; Burak Turhan, A.; Soukoulis, C.M.; Özbay, Ekmel
We designed, fabricated, and experimentally characterized thin absorbers utilizing both electrical and magnetic impedance matching at the near-infrared regime. The absorbers consist of four main layers: a metal back plate, dielectric spacer, and two artificial layers. One of the artificial layers provides electrical resonance and the other one provides magnetic resonance yielding a polarization independent broadband perfect absorption. The structure response remains similar for the wide angle of incidence due to the sub-wavelength unit cell size of the constituting artificial layers. The design is useful for applications such as thermal photovoltaics, sensors, and camouflage. ©2011 Optical Society of America.
Open Access
Phonon-assisted nonradiative energy transfer from colloidal quantum dots to monocrystalline bulk silicon
(IEEE, 2012) Yeltik, Aydan; Güzeltürk, Burak; Hernandez-Martinez, Pedro L.; Demir, Volkan Demir
Silicon is one of the most dominant materials in photovoltaics. To increase optical absorption of silicon solar cells, colloidal quantum dots (QDs) have been proposed as a good sensitizer candidate owing to their favorably high absorption cross-section and tunable emission and absorption properties. To this end, QD sensitization of silicon has previously been studied by mostly facilitating radiative energy transfer (RET) [1,2]. Although RET based sensitization has achieved a considerable increase in conversion efficiencies in silicon photovoltaics, RET is fundamentally limited due to the effective coupling problem of emitted photons to silicon. Alternatively, nonradiative energy transfer (NRET), which relies on near field dipole-dipole coupling [3], has been shown to be feasible in sensitizer-silicon hybrid systems [4-8]. Although colloidal QDs as a sensitizer have been used to facilitate NRET into silicon, the detailed mechanisms of NRET to an indirect bandgap nonluminecent material, together with the role of phonon assistance and temperature activation, have not been fully understood to date. In this study, we propose a QD-silicon nanostructure hybrid platform to study the NRET dynamics as a function of temperature for distinct separation thicknesses between the donor QDs and the acceptor silicon plane. Here, we show NRET from colloidal QDs to bulk Si using phonon assisted absorption, developing its physical model to explain temperature-dependent lifetime dynamics of NRET in these QD-Si hybrids. © 2012 IEEE.
Open Access
Plasmonically enhanced hot electorn based optoelectronic devices
(2015-06) Atar, Fatih Bilge
Hot electron based optoelectronic devices have been regarded as cost-e ective candidates to their conventional counterparts. The efficiency of conventional optoelectronic devices that rely on semiconductor photo-absorbers are mainly limited by the energy bandgap of the semiconductor. On the other hand, hot electron devices can overcome this limitation via the \internal photoemission" mechanism. Absorbed photons give their energy to free electrons of the metal and these high energy (\hot") electrons can be used to generate photocurrent in proper device configurations. High optical re ection from metals has remained as the main drawback of this photocurrent generation scheme but this problem has recently been addressed by the use of surface plasmons. Optical energy can be tightly confined to a metal layer or metal nanostructures in the form of surface plasmons, and the decay of surface plasmons in metals generates hot electrons. In this work, we study mechanisms of surface plasmon excitation, surface plasmon decay, hot electron generation and hot electron photoemission for photocurrent generation. We demonstrate novel device architectures and plasmon excitation structures. We demonstrate the use of such layers for plasmon enhanced hot electron based photodetectors and photovoltaic devices. A metal-semiconductor Schottky junction diode structure is used as hot electron photodetector. A double metal-insulator-metal (MIM) architecture is proposed as a hot electron photovoltaic device. Full wave electromagnetic simulations of these device structures are conducted to provide insight into the surface plasmon assisted hot electron generation process and give future directions in this field.
Open Access
Plasmonically enhanced hot electron based photovoltaic device
(Optical Society of American (OSA), 2013) Atar F.B.; Battal, E.; Aygun L.E.; Daglar, B.; Bayındır, Mehmet; Okyay, Ali Kemal
Hot electron photovoltaics is emerging as a candidate for low cost and ultra thin solar cells. Plasmonic means can be utilized to significantly boost device efficiency. We separately form the tunneling metal-insulator-metal (MIM) junction for electron collection and the plasmon exciting MIM structure on top of each other, which provides high flexibility in plasmonic design and tunneling MIM design separately. We demonstrate close to one order of magnitude enhancement in the short circuit current at the resonance wavelengths. © 2013 Optical Society of America.
Open Access
Semiconductor thin film based metasurfaces and metamaterials for photovoltaic and photoelectrochemical water splitting applications
(WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Ghobadi, Amir; Ghobadi, Türkan Gamze Ulusoy; Karadaş, Ferdi; Özbay, Ekmel
In both photovoltaic (PV) and photoelectrochemical water splitting (PEC‐WS) solar conversion devices, the ultimate aim is to design highly efficient, low cost, and large‐scale compatible cells. To achieve this goal, the main step is the efficient coupling of light into active layer. This can be obtained in bulky semiconductor‐based designs where the active layer thickness is larger than light penetration depth. However, most low‐bandgap semiconductors have a carrier diffusion length much smaller than the light penetration depth. Thus, photogenerated electron–hole pairs will recombine within the semiconductor bulk. Therefore, an efficient design should fully harvest light in dimensions in the order of the carriers' diffusion length to maximize their collection probability. For this aim, in recent years, many studies based on metasurfaces and metamaterials were conducted to obtain broadband and near‐unity light absorption in subwavelength ultrathin semiconductor thicknesses. This review summarizes these strategies in five main categories: light trapping based on i) strong interference in planar multilayer cavities, ii) metal nanounits, iii) dielectric units, iv) designed semiconductor units, and v) trapping scaffolds. The review highlights recent studies in which an ultrathin active layer has been coupled to the above‐mentioned trapping schemes to maximize the cell optical performance.
Open Access
Semiconductor-less photovoltaic device
(IEEE, 2013) Atar, Fatih B.; Battal, Enes; Aygun, Levent E.; Dağlar, Bihter; Bayındır, Mehmet; Okyay, Ali Kemal
We demonstrate a novel semiconductor-less photovoltaic device and investigate the plasmonic effects on this device structure. The device is made of metal and dielectric layers and the operation is based on hot carrier collection. We present the use of surface plasmons to improve energy conversion efficiency. The field localization provided by surface plasmons confine the incident light in the metal layer, increasing the optical absorption and hot electron generation rate inside the metal layer. The device consists of two tandem MIM (metal-insulator-metal) junctions. Bottom MIM junction acts as a rectifying diode and top MIM junction is used to excite surface plasmons. The device operation principle as well as the topology will be discussed in detail. © 2013 IEEE.
Open Access
State of the art and prospects for Halide Perovskite nanocrystals
(American Chemical Society, 2021-06-17) Dey, A.; Ye, J.; De, A.; Debroye, E.; Ha, S. K.; Bladt, E.; Kshirsagar, A. S.; Wang, Z.; Yin, J.; Wang, Y.; Quan, L. N.; Yan, F.; Gao, M.; Li, X.; Shamsi, J.; Debnath, T.; Cao, M.; Scheel, M. A.; Kumar, S.; Steele, J. A.; Gerhard, M.; Chouhan, L.; Xu, K.; Wu, X-g; Li, Y.; Zhang, Y.; Han, C.; Dutta, A.; Vincon, I.; Rogach, A. L.; Nag, A.; Samanta, A.; Korgel, B. A.; Shih, C.-J.; Gamelin, D. R.; Son, D. H.; Zeng, H.; Zhong, H.; Sun, H.; Demir, Hilmi Volkan; Scheblykin, I. G.; Mora-Seró, I.; Stolarczyk, J. K.; Zhang, J. Z.; Feldmann, J.; Hofkens, J.; Luther, J. M.; Pérez-Prieto, J.; Li, L.; Manna, L.; Bodnarchuk, M. I.; Kovalenko, M. V.; Roeffaers, M. B. J.; Pradhan, N.; Mohammed, O. F.; Bakr, O. M.; Yang, P.; Müller-Buschbaum, P.; Kamat, P. V.; Bao, Q.; Zhang, Q.; Krahne, R.; Galian, R. E.; Stranks, S. D.; Bals, S.; Biju, V.; Tisdale, W. A.; Yan, Y.; Hoye, R. L. Z.; Polavarapu, L.
Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.
Open Access
π-Conjugated nanostructured materials: preparation, properties and photonic applications
(Royal Society of Chemistry, 2019) Tuncel, Dönüş
This article reviews recent advances in π-conjugated nanostructures based on conjugated oligomers and polymers, focusing on their preparation, energy transfer abilities, optoelectronic and laser applications, and photophysical properties including light harvesting. This is a rapidly evolving field as these materials are expected to have many important applications in areas such as light-emitting diodes, solid-state lighting, photovoltaics, solid-state lasers, biophotonics, sensing, imaging, photocatalysis, and photodynamic therapy. Other advantages of these materials are their versatility, and consequently, their adaptability to diverse fields.