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    Green Photonics Presentations

    Renewable Energy Generation: Fusion and Photovoltaics: Part II
    (ordered chronologically by session start time)

    Optical and photovoltaic properties of silicon wire solar cells with controlled ZnO nanorods antireflection coating
    Paper 8987-64

    Author(s):  Jae Hyun Kim, Daegu Gyeongbuk Institute of Science & Technology (Korea, Republic of), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 12: Energy Harvesting Storage: Materials and Devices
    Date and Time: 2/5/2014 10:00AM

    Nano and micro-structured three-dimensional (3D) Si has been attracting much attention for future applications in photovoltaic devices due to their superior properties. A new type of silicon micro-wire (SiMW) solar cell with a conformal zinc oxide (ZnO) nanorods anti-reflection coating (ARC) were fabricated. Radial p-n junction was formed in vertically aligned silicon micro-wire solar cell. The vertically aligned silicon micro-wire arrays were fabricaged by optimized metal assisted etching. It iwas found that the combination of Si wire geometry and ZnO ARC was very efficient to maximize the light absorption and to minimize the light reflectance. The growth time of ZnO nanorods were varied from 1 hr to 4 hr. The best efficiency of solar cell was obtained in the sample that has ZnO nanorods grown for 4 hr. The Illuminated current–voltage (I–V) results showed that the photovoltaic efficiency of SiMW solar cells with optimized ZnO ARC was enhanced more than 50% and the short-circuit current density was improved by over 43% compared to SiMW solar cells without ZnO ARC.


    Small molecule organic solar cells: from molecules to devices
    Paper 8981-34

    Author(s):  Karl Leo, Technische Univ. Dresden (Germany), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 9: Advances in Organic Photovoltaics
    Date and Time: 2/5/2014 10:30AM

    In this talk, will discuss recent work on small-molecule organic solar cells. One central research area is the design of suitable molecules which form the bulk heterojunction active layer. A key challenge of the field is to find design rules which relate the molecular structure of absorber materials to layer morphology and cell properties. Furthermore, I will discuss highly efficient tandem structures with optimized electrical and optical properties. Structures based on these approaches have reached efficiencies of 12% and have the potential to reach approximately 20%. Furthermore, these high-efficiency cells also show already reasonable lifetimes.


    Efficient small-molecule photovoltaic cells using nanostructured template
    Paper 8983-37

    Author(s):  Tetsuya Taima, Kanazawa Univ. (Japan), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session 9: OPV
    Date and Time: 2/5/2014 10:30AM

    To improve the efficiency of organic photovoltaic cell (OPV), the control of the crystallinity and morphology of organic thin films is important. We reported the introduction of 3D nano-pillars or 2D nano-sheets of copper iodide on ITO in order to control the organic films at molecular level. Here we report the introducing of the organic templating film (DIP organic semiconductor) for realizing organic nano-pillars. Finally, we obtained a two-fold increase in power conversion efficiency from 2.6 ± 0.2% to 5.2 ± 0.3% at planer heterojunction OPV cells with DIP organic template.


    Patterning of photoelectrode for I2-free solid-state dye-sensitized solar cells
    Paper 8983-41

    Author(s):  Byeonggwan Kim, Yonsei Univ. (Korea, Republic of), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session 9: OPV
    Date and Time: 2/5/2014 11:40AM

    Patterning of light reflecting photonic photoelectrodes has received a lot of attention as a means of enhancing the photoconversion efficiency of solar cells. In particular, nanopatterning by soft imprinting method provides a simple and facile process for a large area well-arrayed mesoporous inorganic oxide films at low cost by using readily available pastes and elastomeric stamps. The nanopatterned photoelectrode enhanced the light-harvesting efficiency of dye-sensitized solar cells (DSSCs) according to light-trapping principles. The I2-free solid-state DSSCs showed a 40% increase in the short-circuit current density and high photoconversion efficiency (7.03%) which is one of the highest values reported for N719-dye-based, I2-free solid-state DSSCs. This universal patterning method will improve performance in various photovoltaic cells and optoelectric devices using mesoporous inorganic oxide films.


    Hybrid bulk heterojunction solar cells based on low band gap polymers and CdSe nanocrystals
    Paper 8981-37

    Author(s):  Sergey V. Dayneko, National Research Nuclear Univ. MEPhI (Russian Federation), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 9: Advances in Organic Photovoltaics
    Date and Time: 2/5/2014 11:50AM

    Bulk heterojunction polymer solar cells are inexpensive, can be layered onto flexible surfaces and show great promise for photovoltaics. The use of acceptors with wide absorption spectra, high extinction coefficients and charge mobilities (i.e., semiconductor nanocrystals), is a good strategy for increasing the efficiency of these solar cells. We have compared the photophysical properties of bulk heterojunction polymer solar cells made of the most promising polymers (PCDTBT and PTB7) and CdSe quantum dots. PTB7 solar cells are more efficient than PCDTBT cells. The nanocrystal size strongly affects the photophysical characteristics and efficiency of the cells.


    Energy generation and storage: combining ZnO piezogenerators and graphene-based ultracapacitors
    Paper 8987-69

    Author(s):  Vinod E. Sandana, Graphos (France), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 13: Energy Harvesting Storage: Metal Oxides and Graphene
    Date and Time: 2/5/2014 11:50AM

    Graphene and ZnO are both remarkable, multifunctional materials with distinctive and unique property sets [1,2] and their synergy opens up uncharted possibilities. For instance, highly conductive graphene-based ultracapacitors are currently considered to be one of the most promising energy storage devices [3] while ZnO (with one of the largest piezoelectric coefficients of any semiconductor) is a leading piezogenerator material [2]. In this paper, we investigate the potential of the combining of graphene ultracapacitors and ZnO nanogenerators for the production of new generation of nanodevices integrating energy generation and storage. [1] V.E. Sandana et al Proc. of SPIE Vol. 8626 (2013) 822603 [2] D. J. Rogers et al. Proc. of SPIE Vol. 8263 (2012) 82631X-1 [3] J. Li et al. Graphene,1 (2012) 1-13


    Engineering metal oxide structures for efficient photovoltaic devices
    Paper 8987-70

    Author(s):  Isabella Concina, Univ. degli Studi di Brescia (Italy), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 13: Energy Harvesting Storage: Metal Oxides and Graphene
    Date and Time: 2/5/2014 12:10PM

    Metal oxide-based photoanodes are critical components of dye sensitized solar cells (DSCs), which promise to have several benefits as compared with their traditional counterparts, relying in particular on the possibility to access greener energy. A careful engineering of the metal oxide-based composing photoanode, as well a process design devoted to reduce as much as possible the environmental impact of device fabrication, are strategic in order to both improve device performances and plan a near future production scale up. Herein we present and discuss how to apply these criteria in order to boost ZnO-based DSC performances.


    Analytical modeling of III-V solar cells close to the fundamental limit
    Paper 8981-38

    Author(s):  Matthew P. Lumb, U.S. Naval Research Lab. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 10: Photovoltaics Modeling: Joint Session with Conferences 8980 and 8981
    Date and Time: 2/5/2014 1:40PM

    A highly effective strategy of photon management is to use a back surface reflector (BSR). In this work, we present a full analytical model incorporating effects from both the modified generation function and photon recycling in GaAs solar cells with a BSR. We discuss the impact of doping concentration, non-radiative recombination, solar cell dimensions and BSR reflectivity on the efficiency, and compare the prediction of the device models to experimental data measured on GaAs devices. We use the model to predict the performance of alternative III-V materials, such as InP, comparing the predicted performance to state-of-the-art GaAs solar cells.


    Towards numerical simulation of nonhomogeneous thin-film silicon solar cells
    Paper 8981-39

    Author(s):  Tom H. Anderson, The Univ. of Edinburgh (United Kingdom), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 10: Photovoltaics Modeling: Joint Session with Conferences 8980 and 8981
    Date and Time: 2/5/2014 2:10PM

    Electrical and optical properties of a thin film solar cell made of alloys of amorphous silicon were studied theoretically. The solar cell was backed by a periodically corrugated metallic back reflector. The intrinsic layer of the solar cell was taken to be nonhomogeneous normal to the metal/semiconductor interface. The nonhomogeneity in the semiconductor was supposed to result from the nonhomogeneity in the composition of the amorphous silicon. The drift-diffusion model was used for the computation of the current-voltage characteristics of the cell. The photovoltaic efficiency of the solar cell was computed as a function of the incidence angle by assuming an AM1.5 solar irradiance spectrum.


    Optimizing light absorption in a thin film p-i-n solar cell using a quasi-periodic grating
    Paper 8980-38

    Author(s):  Mahmoud Atalla, The Pennsylvania State Univ. (United States), et al.
    Conference 8980: Physics and Simulation of Optoelectronic Devices XXII Session 10: Photovoltaics Modeling: Joint Session with Conferences 8980 and 8981
    Date and Time: 2/5/2014 2:30PM

    A p-i-n solar cell is best suited for strong absorbers with poor collection capabilities. However, the absorption naturally decreases at photon energies close to the electronic bandgap of the semiconductor. We hypothesized that a quasi-periodic surface textures in the role of diffraction gratings at the back contact can efficiently scatter light increasing the optical path length inside the absorber layer. The effect of quasi-periodic corrugated backing metallic contact of various types was studied theoretically. To help optimizing the design of the quasi periodic grating the corresponding canonical problem was considered. The absorption of light was calculated using the rigorous coupled-wave approach for an AM1.5 solar irradiance spectrum. The n- and i-layers consist of isotropic nonhomogeneous multilayered semiconductor


    Factors limiting the efficiency of laser power converters under low- and high-intensity illumination
    Paper 8981-58

    Author(s):  Jayanta Mukherjee, Univ. of Surrey (United Kingdom), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 10: Photovoltaics Modeling: Joint Session with Conferences 8980 and 8981
    Date and Time: 2/5/2014 2:50PM

    We report on the role of various non-radiative recombination mechanisms responsible for limiting the conversion efficiency of III-V based laser power converters (LPCs) for optical power transfer applications. Comparing theoretical modelling with temperature-, wavelength- and intensity-dependent characterization of the LPC, we separate the intensity regimes where series resistance and Auger-recombination begin to dominate over defect recombination. As the LPC forms an excellent prototypical system for probing fundamental efficiency limits of PVs, this study gives useful insights into the design and material improvements required for conversion efficiency scaling in future solar cells, for applications under normal, as well as concentrated, illumination.


    Ga-rich Ga(x)In(1-x)P solar cells on Si with 1.95 eV bandgap for ideal III-V/Si photovoltaics
    Paper 8981-41

    Author(s):  Christopher Ratcliff, The Ohio State Univ. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 11: Advances in Multijunction Materials and Devices
    Date and Time: 2/5/2014 4:10PM

    Theoretical models for III-V compound multijunction solar cells show that solar cells with bandgaps of 1.95-2.3 eV are needed for ideal optical partitioning of the solar spectrum for III-V/Si device architectures containing three or more junctions. Here, Ga-rich GaInP materials and solar cells are grown, fabricated and tested, having bandgaps from 1.95 eV to 2.1 eV, on Si via GaAsP buffer layers. These are compared with identical cells grown on GaAs and GaP substrates. High open-circuit voltage values are achieved and are observed to track defect density as a function of substrate material.


    Detailed physics based modeling of triple-junction InGaP/GaAs/Ge solar cell
    Paper 8981-42

    Author(s):  Alexandre I. Fedoseyev, CFD Research Corp. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 11: Advances in Multijunction Materials and Devices
    Date and Time: 2/5/2014 4:30PM

    We have developed a detailed physics based 3D TCAD model of a triple-junction photovoltaic (TJ PV) cell, and calibrated the various physical parameters to match experimental data (dark and light JV). Simulation results of light JV characteristics and external quantum efficiency (EQE) of a triple junction InGaP/GaAs/Ge solar cell are demonstrated. The calculated performance parameters compare well against measured experimental data of a Spectrolab triple-junction InGaP/GaAs/Ge cell [1]. REFERENCES [1] NH Karam, RR King, BT Cavicchi, et al. IEEE Transactions on Electron Devices, Vol. 46, No. 10, 1999


    Three-dimensional ceramic molding process based on microstereolithography for the production of piezoelectric energy harvesters
    Paper 8970-14

    Author(s):  Shoji Maruo, Yokohama National Univ. (Japan), et al.
    Conference 8970: Laser 3D Manufacturing Session 3: Multi-photon Polymerization of 3D Micro- and Nanostructures II
    Date and Time: 2/5/2014 5:40PM

    We have developed a three-dimensional (3-D) ceramic molding process based on microstereolithography to produce 3-D piezoelectric energy harvesters. To make finer piezoelectric elements with high production yield, we have developed a photopolymer suitable for thermal decomposition at low temperature. A prototype of the spiral-shaped piezoelectric element was fabricated. The electric power generation using the spiral-shaped element was demonstrated in 3-D vibration experiments. The piezoelectric effect of the spiral-shaped element was also analyzed by COMSOL multiphysics. As a result, we found that the electric power could be drastically improved by optimizing electrode pattern attached to the spiral-shaped element.


    Design strategy for low emissivity windows with effective insulation
    Paper 8981-53

    Author(s):  Mike P. Watts, Impattern Solutions (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Low emissivity windows are a critical element of designing energy efficient structures. There are 4 energy bands that contribute to energy transfer in windows; visible radiation, solar near IR radiation, re-radiated mid IR and thermal convection. Analytical models were developed for thermal transfer, and re-radiation transfer. Based on industry standard model programs, the best windows were triple pane with low conductivity gas fill, multiple silver coatings to reject the re-radiated mid IR, and different multilayer stacks to transmit the visible while either blocking or transmitting the near solar IR.


    The optimization of textured a-Si:H solar cells with a fully three-dimensional simulation
    Paper 8981-59

    Author(s):  Chun-Yao Lee, National Taiwan Univ. (Taiwan), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    In this research, we studied textured a-Si:H solar cells by using three dimensional(3D) simulation programs including 3D finite-difference time-domain method and 3D Poisson and drift-diffusion solver. With these fully 3D models without much approximation, we can calculate the real device performance with higher accuracy. For the random-rough surface, we found that structures with the average roughness equal to 30.60 nm and the root mean square (rms) roughness equal to 38.50 nm have the maximal energy conversion efficiency due to the stronger light absorption. Further optimization will be discussed in this paper.


    Be implant activation and damage recovery study in N-type GaSb
    Paper 8981-63

    Author(s):  Nassim Rahimi, The Univ. of New Mexico (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Characteristics of ion implantation induced damages in GaSb, and their removal by rapid thermal annealing are investigated by X-Ray Diffraction spectrometry and Transmission Electron Microscopy. The activation of implanted Be ions in GaSb using Capacitance-Voltage measurements is studied in details. Rapid thermal annealing has been implemented for different times and temperatures and different configurations are tested to avoid Sb outdiffussion during RTA process. Results indicate a lattice quality that is close to pristine GaSb for samples annealed at 600 °C for 10s using thick Si3N4 capping layer. Electrical response of diodes is measured and excellent diode behavior is observed.


    Cheap and efficient plasmonic solar cell
    Paper 8981-65

    Author(s):  Ahmed E. Khalifa, The American Univ. in Cairo (Egypt), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Plasmonic solar cell is a very promising structure for high efficient solar cell application. It has some unique characteristics that allow high energy localization and higher solar energy absorption. Most of the proposed designs are based on using noble metals such as gold and silver to achieve the plasmonic effect. These metals are, however, expensive and increase the cost of the solar cell. Thus, the need to propose novel and cheap material with plasmonic like effect is of prime importance. In this work we demonstrate the applications of TiN that has good plasmonic like effect over wide bandwidth. A detailed comparative study of TiN and conventional plasmonic material is presented and optimized solar designs are proposed.These designs have comparable field localization and light scattering effects to those of the conventional plasmonic material. In addition TiN is more compatible with the CMOS fabrication technology than the conventional plasmonic metals, which can even ease the integration with other optoelectric devices . Should the electrical performance be further studied and optimized, the overall efficiency of the solar cell can be maintained and/or enhanced and total cost/watt dramatically reduced.


    NIR-sensitive conductive polymers for transparent electrochromic photo-thermo-electric converters
    Paper 8983-56

    Author(s):  Byeonggwan Kim, Yonsei Univ. (Korea, Republic of), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Conductive polymers have received significant attention for applications in optoelectronics such as electrochromic devices (ECDs), photovoltaic cells, organic light emitting diodes, and light sensors due to their controllable optical and photo-thermo-electrical properties by external electrical stimuli. These properties of hexyl-derivatized poly(3,4-ethylenedioxyselenophene) are clearly demonstrated by precisely controlling the doping state and the surface morphology from applying potential of the flexible polymer films. Especially, the doped polymer film at –0.1 V reveals the highest photothermal conversion efficiency and a power factor of 42.5% and 354.7 μW m−1 K−2, respectively. Efficient visible to near-infrared absorption, photon to heat, and heat to electric conversion has been realized in one transparent and potentially optimized film that could benefit in exploiting invisible NIR sensors, multifunctional film displays, day and night vision display, optical attenuators, and photodynamic theragnosis.


    Nanostructured conductive polymer/GaAs epilayer hybrid heterojunction solar cells
    Paper 8983-57

    Author(s):  Yi-Chun Lai, National Chiao Tung Univ. (Taiwan), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Recently, hybrid solar cells combining organic materails and inorganic semiconductors are extensively researched because of their relatively inexpensive cost and low temperature fabrication processes. In this work, we demonstrate organic/inorganic hybrid heterojunction photovoltaic devices based on gallium arsenide (gaas) substrate and conjugated polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS). We started with a one-dimensional device simulation based on a self-consistent poisson and drift-diffusion solver to investigate the band alignment between PEDOT and GaAs for achieving a practical device design. Next, for device fabrication, we prepare a cleaned and oxide-removed one-side-polished (100) GaAs wafer with a low doping epitaxial layer, followed by thermal evaporation of aluminum as back-side electrode. After that, PEDOT:PSS is spun-cast onto the substrate and then annealed. Finally, shading-ratio-optimized silver fingers are deposited as the anode. In addition to planar ones, we also use self-assembled polystyrene (PS) nanosphere lithography technique to form the sacrificial mask layer, and perform anisotropic inductively coupled plasma reactive ion etching (ICP-RIE) on GaAs substrates. It has been revealed that nanostructures such as nanowires or nanorods allow the conformal p-n heterojunction formation at the interface of organic/inorganic semiconductors, which can be beneficial for both light absorption and carrier collection. The optical and electrical characteristics such as reflectance, current voltage, and external quantum efficiency are measured. Currently, for planar/nanorod devices, we achieve 7.54/7.74 % power conversion efficiencies with open-circuit voltages of 0.662/0.639 V, short-circuit currents of 15.34/20.65 mA/cm2, and fill factors of 74.20/58.67 % under simulated AM1.5G illumination.


    Characteristics of periodic silicon nanorods arrays for conductive polymer/silicon heterojunction solar cells
    Paper 8983-58

    Author(s):  Yi-Chun Lai, National Chiao Tung Univ. (Taiwan), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Mono- and multi-crystalline silicon photovoltaics currently still hold more than 80% market share because of the non-toxic, abundant material resources used, and their long-term stabilities. However, the cost of solar power is still more than three times that of fossil fuels, which necessitates a further reduction to accelerate its widespread use. It has been estimated that cell fabrication consumes 30% of the total manufacturing cost due to energy intensive semiconductor processes, such as high temperature furnace for doping, electrodes co-firing, high-vacuum chemical deposition, etc. Therefore, the organic-inorganic hybrid cell concept has been proposed to take advantage of the solution-based processes for rapid and low-cost production and the wide absorption spectrum of silicon. In this work, we demonstrate a hybrid heterojunction solar cell based on the structure of conductive polymer PEDOT:PSS spun cast on n-type crystalline silicon nanorod (SiNR) arrays with periodic arrangements. The nanorod arrays are fabricated by electron beam (E-beam) lithography followed by reactive-ion etching (RIE), which show capability to enhance light harvesting. In addition, SiNRs and PEDOT:PSS can form core-shell structure that provides a large p-n junction area for carrier separation and collection. However, the reactive-ion etching cause a lot of surface damages on the surface of the rod which cause a lot of interface defect between Silicon and PEDOT:PSS. A post-RIE damage removal etching (DRE) is subsequently introduced in order to mitigate the surface damages issues . Finally, we map the weighting reflection of silicon nanorod arrays with different periods and filling ratio, which explain the reason of lowing reflection of device after DRE treatment and indicate that arrays with 330nm period and 0.25 filling ratio have the minimum weighting reflection.


    Tailor-made ZnO@SnO2 networks for high-efficiency photovoltaic devices
    Paper 8987-82

    Author(s):  Riccardo Milan, Univ. degli Studi di Brescia (Italy), et al.
    Conference 8987: Oxide-based Materials and Devices V Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Increasing interest is addressed to the investigation of SnO2 and ZnO in dye sensitized solar cells. Both are good candidates for working electrodes for their good properties in terms of conduction band positioning and electron mobility. We investigated networks of these compounds and their performances when integrated in dye sensitized solar cell architecture. Optimized structure resulted in photoconversion efficiency as high as 5.0%. Impedance spectroscopy elucidated the physical and chemical mechanisms relying with improved efficiency of these composite systems.


    Nanostructured ZnO for energy-harvesting applications
    Paper 8987-86

    Author(s):  David J. Rogers, Nanovation (France), et al.
    Conference 8987: Oxide-based Materials and Devices V Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    ZnO is a remarkable multifunctional material with a distinctive and unique property set. In particular, it exhibits one of the largest piezoelectric coefficients of any semiconductor and has a relatively high thermoelectric figure-of-merit. This has often led to it being considered for use in piezogenerators [1] and thermoelectric energy harvesting [2]. In this paper, we investigate the enhancement in the potential of ZnO for parallel kinetic and thermal energy scavenging through nanostructuration.


    Silicon solar cell enhancement by plasmonic silver nanocubes
    Paper 8981-44

    Author(s):  Ryan J. Veenkamp, Carleton Univ. (Canada), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 12: Advances in Light Trapping
    Date and Time: 2/6/2014 8:30AM

    Our paper presents a detailed numerical simulation and experimental study of the efficiency enhancement gained by optimizing metal nanocubes incorporated on the surface of silicon solar cells. We investigate the effects of nanoparticle size, surface coverage and spacer layer thickness on solar absorption and cell efficiency. The fabrication of nanocubes on solar cells is also presented, with the trends observed in simulation verified through experimental data. Testing reveals that nanocubes show worse performance than nanospheres when sitting directly on the silicon substrate; however, enhancement exceeds that of nanospheres when particles are placed on an optimized spacer layer of SiO2, for reasonable surface coverages of up to 25%. Our analysis shows that for a large range of particle sizes, 60-100nm, enhancement in light absorption remains at a high level, near the optimum. This suggests a high level of fabrication tolerance which is important due to the chemical growth mechanism used for nanocube synthesis, as it consistently produces nanocubes in that range. Further, we note that efficiency enhancement by nanocubes is influenced by particle size, surface coverage, and spacer layer thickness much differently than that for a spherical geometry, thus our study focuses on the optimization of the nanocube parameters. We show that 80nm nanocubes on a 25nm SiO2 spacer layer realize ~24% enhancement in light absorption compared to an identical particle-free cell. Finally, we present both the numerical and experimental results for silicon solar cells coated with nanocube arrays.


    Optimum feature size of randomly textured glass substrates for maximum scattering inside thin-film silicon solar cells
    Paper 8981-47

    Author(s):  Nasim Sahraei, National Univ. of Singapore (Singapore), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 12: Advances in Light Trapping
    Date and Time: 2/6/2014 9:10AM

    In this work we will show the optimum morphological criteria for optimum light scattering in a-Si:H solar cells for Aluminium Induced Textured (AIT) glass. Haze can be easily measured for the substrate/air interface. However, the relevant scattering properties are those in the absorber material, which cannot be measured directly but can be calculated with a suitable method. The available models for haze calculation based on scalar scattering theory cannot correctly estimate the haze value because the lateral feature size and the opening angel of the haze measurement is not considered in the model. In this work, we demonstrate that the power spectral density (PSD) function of the randomly textured surface can provide the missing information in the haze equation.


    Optical scattering by anodized aluminum oxide for light management in thin film photovoltaics
    Paper 8981-49

    Author(s):  Brian Roberts, Univ. of Michigan (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 12: Advances in Light Trapping
    Date and Time: 2/6/2014 9:50AM

    We investigate the optical scattering properties of self-assembled nanoporous anodized aluminum oxide (AAO) films, and propose integrating AAO as a backscattering layer for light management in thin film photovoltaics. Angle selective scattering and direction of light to extreme, near-horizontal angles can enable new functionality for semitransparent PV window coatings, allowing improved absorption of direct sunlight without sacrificing transparency in the normal direction. Scattering to extreme angles can also be exploited to aid light trapping in thin epitaxial semiconductor absorbers, without texturing.


    InP-based nano solar cells
    Paper 8981-51

    Author(s):  Florian Proise, Institut de Recherche et Développement sur l'Energie Photovoltaïque (France), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 13: Physics of Nano-Engineered Photovoltaics II
    Date and Time: 2/6/2014 10:40AM

    This paper aims at studying the case of photovoltaic nano-cells smaller than photons wavelength designing optical nano-antenna to couple the incoming light with nano-cells. Theoretical results show that more than 60% of the broad-band incoming solar spectrum can be absorbed with only 300 nm absorber thickness and a 1/3 coverage fraction. We show that this kind of structure has been done using clean room process. The electrical behaviour is also studied with nano-diodes current-voltages measuements and passivation issues are tackled with a film of polyphiosphazen, characterized with XPS, EDX, photoluminescence, time-resolved photoluminescence and hyperspectral Imager measurements.


    Dedicated nanoantenna element for vertical nanorods in plasmonic photovoltaics
    Paper 8981-52

    Author(s):  Hossein Alisafaee, The Univ. of North Carolina at Charlotte (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 13: Physics of Nano-Engineered Photovoltaics II
    Date and Time: 2/6/2014 11:10AM

    We investigate a novel light conversion scheme in nanostructures for the highly demanding field of plasmonic solar cells. In our study, we incorporate vertical nanorods made of semiconductor materials, which are coupled optically to plasmonic nanoantennas for optimal absorption of sunlight. Utilizing the unique properties of localized surface plasmon resonances, we create dedicated nanoantenna elements such that emission pattern is effectively directed toward the absorber material. In our approach, we use a computational finite element method to investigate the effects of size and shape of metallic nanoparticles to obtain an asymmetric radiation pattern that matches the geometry of our design.


    Extending the operational wavelength of thermophotovoltaics through superlattice and barrier engineering
    Paper 8981-64

    Author(s):  Abigail S. Licht, Tufts Univ. (United States), et al.
    Conference 8981: Physics, Simulation, and Photonic Engineering of Photovoltaic Devices III Session 13: Physics of Nano-Engineered Photovoltaics II
    Date and Time: 2/6/2014 11:30AM

    In this presentation we detail our research on mid-infrared wavelength thermophotovoltaic (TPV) diodes which hold the potential for a wide array of applications due to their ability to work with lower temperature sources (< 1000°C). We discuss simulation results using on the optimization of 5 micron Eg structures utilizing type two strained layer GaSb/InAs superlattice cells. The p I n diode structure is compared with the pBn structure. The performance of the simulated diodes is compared with experimental results of diodes fabricated by molecular beam epitaxy with standard photolithography contact deposition and characterization by calibrated blackbody sources.


    Rapid composition analysis of compound semiconductor thin film solar cell by laser induced breakdown spectroscopy
    Paper 8967-39

    Author(s):  Suk-Hee Lee, Gwangju Institute of Science and Technology (Korea, Republic of), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 14: Processing and Diagnostics of Photovoltaics
    Date and Time: 2/6/2014 2:00PM

    The efficiency of Cu(In,Ga)Se2 (CIGS) thin film solar cells sensitively depend on the elemental composition and compositional ratios of constituent elements. A rapid verification of composition during the CIGS solar cell manufacturing can ensure the production of high quality products. Laser-induced breakdown spectroscopy (LIBS) satisfies the conditions for rapid verification and has the potential to be applied for an in-situ monitoring of CIGS solar cell composition at manufacturing sites. This paper presents the calibration results of CIGS LIBS signal and the effects of process parameters on the accuracy and precision of predicted elemental composition.


    Modeling of laser patterning of thin-film solar cells
    Paper 8967-40

    Author(s):  Thomas Peschel, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 14: Processing and Diagnostics of Photovoltaics
    Date and Time: 2/6/2014 2:20PM

    We present theoretical models describing the interaction of laser pulses with thin-film structures of solar cells. A model of light propagation is used to determine the distribution of absorbed laser power. Depending on the wavelength absorption occurs in different depths with consequences for the efficiency of ablation. Direct or multi-photon absorption and impact ionization drive the evolution of the carrier density which in turn modifies the light propagation and the absorbed power. An additional thermo-mechanical model is used to evaluate the effect of the absorbed power on the generation of internal stresses, ablation behavior and the size of heat-affected zones.


    Tailoring liquid/solid interfacial energy transfer: fabrication and application of multiscale metallic surfaces with engineered heat transfer and electrolysis properties via femtosecond laser surface processing techniques
    Paper 8968-27

    Author(s):  Troy Anderson, Univ of Nebraska-Lincoln (United States), et al.
    Conference 8968: Laser-based Micro- and Nano-Processing VIII Session 6: Additive Manufacturing and Advanced Deposition Processes
    Date and Time: 2/6/2014 2:20PM

    Femtosecond Laser Surface Processing (FLSP) is a powerful technique for the fabrication of self-organized multiscale surface structures on metals that are critical for advanced control over energy transfer at a liquid/solid interface. We demonstrate an undocumented range of such multiscale surface features on stainless steel and nickel using FLSP and utilize this wide range of multiscale surfaces to tailor liquid/solid energy transfer; the onset of film boiling (characterized by the Leidenfrost temperature) can be increased by over 175°C, droplets on a surface can be propelled uphill via directional boiling, and the production efficiency of hydrogen via electrolysis can be increased.


    Optimizing process time of laser drilling processes in solar cell manufacturing by coaxial camera control
    Paper 8967-41

    Author(s):  Volker Jetter, Fraunhofer-Institut für Physikalische Messtechnik (Germany), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 14: Processing and Diagnostics of Photovoltaics
    Date and Time: 2/6/2014 2:40PM

    Without control, the processing time of laser drilling processes is determined by the maximum wafer thickness occurring during production. For silicon solar cell wafers, this value typically varies about ±20 %. This article describes a coaxial camera control system observing the bottom breakthrough of via holes from the laser side. A novel “cellular neural network” (CNN) camera enables latency times below 100 µs for both, image acquisition and processing of the emissions from every single laser pulse. The result is a quality control system reducing processing time to the one required for aver-age instead for maximum wafer thickness.


    Silver-free solar cell interconnection by laser spot welding of thin aluminum layers: analysis of process limits for ns- and µs-lasers
    Paper 8967-48

    Author(s):  Henning Schulte-Huxel, The Institut für Solarenergieforschung Hameln (Germany), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 14: Processing and Diagnostics of Photovoltaics
    Date and Time: 2/6/2014 3:00PM

    Damage-free contacting of 2 to 20-µm-thin metal layers on solar cells for interconnection is a challenge in Si-photovoltaics. To reduce material consumption and mechanical stress, the layer thickness should be minimized without inducing crystal damage. We present a laser process which welds a 10-µm-thick Al-film to Al-metallized cells. The limiting thickness of cell metallization for a ns- and µs-laser system is analyzed. The laser induced damage is investigated by the degradation of effective charge carrier lifetime of 1 to 20 µm Al-metallized, SiNx-passivated Si-wafer. The mechanical properties and electrical contact resistance of the micro-welds spots are determined.


    New strategies in laser processing of TCOs for light management in thin-film silicon solar cells
    Paper 8968-30

    Author(s):  Carlos Molpeceres, Univ. Politécnica de Madrid (Spain), et al.
    Conference 8968: Laser-based Micro- and Nano-Processing VIII Session 7: Photovoltaics and Energy Devices: Joint Session with Conferences 8967 and 8968
    Date and Time: 2/6/2014 3:50PM

    This work studies two strategies to improve light management in thin film silicon solar cells using laser technology. The first one addresses the problem of TCO surface texturing using fully commercial laser sources. In particular AZO and ITO samples has been laser processed and the results has been optically evaluated measuring the haze factor of the treated samples. On the other hand, laser annealing experiments of TCOs doped with rare earth ions are presented as a potential process to produce layers with upconversion properties, opening the possibility of its potential use in high efficiency solar cells


    Adjustable spectrum LED solar simulator
    Paper 9003-43

    Author(s):  Kurt J. Linden, Spire Corp. (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 11: Solid State Lighting II
    Date and Time: 2/6/2014 4:00PM

    A spectrally-tunable solar simulator combining the light from 23 different wavelength LEDs now makes it possible to evaluate the individual cell layers comprising the new generation of high-efficiency tandem solar cells. This simulator eliminates the high-voltage circuitry required for conventional xenon lamp based simulators and is more reliable. The electronically-tunable simulator operated via a graphical user interface and covering the entire 350-1100 nm spectral range has a demonstrated intensity and spectral uniformity better than 1% across a 156 mm x 156 mm solar cell area and is modular in design, facilitating simulator size scaling to arbitrarily large solar module sizes.


    Optimized laser patterning for high performance Cu(In,Ga)Se2 thin-film solar modules
    Paper 8967-43

    Author(s):  Andreas Burn, Berner Fachhochschule Technik und Informatik (Switzerland), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 15: Photovoltaics and Energy Devices: Joint Session with Conferences 8967 and 8968
    Date and Time: 2/6/2014 4:20PM

    Solar cells based on Cu(In,Ga)Se2 absorbers show the highest efficiencies among all thin-film technologies. Despite a recent slowdown of the thin-film market growth CIGS production capacity is increasing and the technique is maturing. Apart from the cell technology itself, module patterning is a major critical point in the production process. The scribing tool of choice is the laser but finding the right process parameter has proven to be difficult for this complex material system. In the past years we conducted a comprehensive study on laser sources and parameters for selective ablation of photovoltaic thin-films. Various aspects have been analyzed in-depth and were presented at previous conferences. Among the many scribing processes studied we identified a reliable and robust “workhorse” process which has a high potential for use in an industrial production line. The selected picosecond laser process is well controllable and can be competitively implemented in an industrial environment. In the present study we show the successful realization of functional CIGS mini modules on glass substrate with optimized dead-zone. We demonstrate reproducible scribing of interconnects smaller than 70 μm on 8-cell modules. This translates into a productive area loss due to scribing of considerably less than 2 percent. The produced mini modules achieved certified conversion efficiencies of up to 16.61 percent.


    Quasi-simultaneous laser soldering for the interconnection of back-contact solar cells with composite foils
    Paper 8968-31

    Author(s):  Simon W. Britten, Fraunhofer-Institut für Lasertechnik (Germany), et al.
    Conference 8968: Laser-based Micro- and Nano-Processing VIII Session 7: Photovoltaics and Energy Devices: Joint Session with Conferences 8967 and 8968
    Date and Time: 2/6/2014 4:40PM

    In this contribution we evaluate laser scanning approaches for the interconnection of the 31 electrical contacts of a MWT-back contact solar cell. The selective energy deposition with a laser system allows the minimization of thermomechanical stress in the joining zone, but requires adapted scanning strategies to prevent damages in the solar cell top layer. The laser scanning process is applied in combination with a composite foil as an interconnector and a pre-dispensed solder paste. This approach is evaluated regarding the joining quality of the interconnection as function of the scanning strategy. An analysis of the thermal distribution on the solar cell by thermography is used for the optimization of the laser scanning strategy in regard to thermomechanical stress in the joining zone.


    Investigations of laser ablation processes in thin-films for photovoltaic applications
    Paper 8967-44

    Author(s):  Paulius Gecys, Ctr. for Physical Sciences and Technology (Lithuania), et al.
    Conference 8967: Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX Session 15: Photovoltaics and Energy Devices: Joint Session with Conferences 8967 and 8968
    Date and Time: 2/6/2014 5:00PM

    The thin-film Cu-chalcopyrite-based solar cell technologies are becoming more attractive due to their lower cost and optimal performance. Serial interconnect formation in these devices is one of the most promising technology for laser applications. Minimization of laser affected area after thin-film processing is crucial for further developments of this technology. Therefore we were concentrating on optimizing the pulse duration for CIGS solar cell scribing and also investigated the possibility of using the laser induced ablation for the P3 type laser processing of CZTSe thin-film solar cells.


    Important Dates

    Abstracts Due
    17 July 2017

    Author Notification
    25 September 2017

    Manuscripts Due
    See Individual Conferences


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    Journal of Photonics for Energy