A Combined Statistical and TCAD Model as a Method for Understanding and Reducing Variations in Multicrystalline Si Solar Cell Production

AbstractMonitoring the I-V parameters in mass production yields a distribution that cannot be understood in a simple manner. For example, if Voc varies greatly, it is not obvious whether this is mainly due to variations in the bulk lifetime or in the surface passivation or due to other sources.In this work, we develop a method where statistics is combined with numerical device modeling to obtain a physical interpretation of the observed variations. In the first part, we derive a multivariate statistical model to extract the main influences of fabrication fluctuations on the I-V parameters. This statistical model is based on cell parameters measured on a representative sample of solar cells from production. In the second part, we develop a computer-aided design (TCAD) device simulation model for multicrystalline Si solar cells. This TCAD model quantifies the I-V variations on a physically sound basis. However, the number of simulations is grossly reduced by feeding in solely the main influences obtained from the statistical model. In the third part, we verify this method by comparing the calculated distribution with production data.This model is used for optimization strategies for higher cell efficiency, smaller variations in cell parameters and improved yield in mass production. Furthermore, we will apply our methodology to advanced cell concepts. It will allow the early consideration of production fluctuation in device simulation of advanced cell concepts, and therefore a realistic assessment of such concepts

High-order-harmonic generation from dense water microdroplets

We report on high-order-harmonic generation from micrometer-sized liquid water droplets. In pump-probe experiments, the influence of the time delay onto the emission of harmonic radiation is systematically studied. Phase-matching aspects are observed by controlling the focal position and the intensity of the probe pulse. The spatiotemporal dynamics of the droplet during interaction with intense laser pulses are studied by controlling the intensity of the pump pulse. We find transient phase-matching conditions and the expansion dynamics of the droplet to be of major influence on the harmonic yield. © 2013 American Physical Society.DFG/EXC/QUESTDFG/KO 3798/1-

Spatial contributions of electron trajectories to high-order-harmonic radiation originating from a semi-infinite gas cell

We report on the analysis of the spatial beam profile of high-order harmonic radiation originating from a semi-infinite gas cell (SIGC). We experimentally assign contributions of electron trajectories to different spatial regions of the harmonic radiation beam. The angular divergence of the harmonic radiation is studied for the first time in a SIGC as a function of different phase-matching parameters. We relate the ratio of the dipole phase coefficients to the coherence time and divergence angle measurements. Simulations, including high-order-harmonic propagation, give further insight into the generation process and the influence of phase matching. The analysis reveals that the SIGC enables tuning of the cutoff frequency by altering the absorption of the generating medium.The authors thank Vasily V. Strelkov and Pascal Salie`res for valuable discussions and the Deutsche Forschungsge- meinschaft DFG and the Cluster of Excellence QUEST for financial support of this work. Carlos Hernández-García and Luis Plaja acknowledge support from Junta de Castilla y León (Consejería de Educación and Fondo Social Europeo) and Spanish MINECO (FIS2009-09522)

Advances in the Surface Passivation of Silicon Solar Cells

AbstractThe surface passivation properties of aluminium oxide (Al2O3) on crystalline Si are compared with the traditional passivation system of silicon nitride (SiNx). It is shown that Al2O3 has fundamental advantages over SiNx when applied to the rear of p-type silicon solar cells as well as to the p+ emitter of n-type silicon solar cells. Special emphasis is paid to the transfer of Al2O3 into industrial solar cell production. We compare different Al2O3 deposition techniques suitable for mass production such as ultrafast spatial atomic layer deposition, inline plasma-enhanced chemical vapour deposition and reactive sputtering. Finally, we review the most recent cell results with Al2O3 passivation and give a brief outlook on the future prospects of Al2O3 in silicon solar cell production

High-order harmonic generation directly from a filament

The synthesis of isolated attosecond pulses (IAPs) in the extreme ultraviolet (XUV) spectral region has opened up the shortest time scales for timeresolved studies. It relies on the generation of high-order harmonics (HHG) from high-power few-cycle infrared (IR) laser pulses. Here we explore experimentally a new and simple route to IAP generation directly from 35 fs IR pulses that undergo filamentation in argon. Spectral broadening, self-shortening of the IR pulse and HHG are realized in a single stage, reducing the cost and experimental effort for easier spreading of attosecond sources. We observe continuous XUV spectra supporting IAPs, emerging directly from the filament via a truncating pinhole to vacuum. The extremely short absorption length of the XUV radiation makes it a highly local probe for studying the elusive filamentation dynamics and in particular provides an experimental diagnostic of short-lived spikes in laser intensity. The excellent agreement with numerical simulations suggests the formation of a single-cycle pulse in the filament. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

Solar cell emitter design with PV-tailored implantation

A potentially cost-effective ion implanter for solar cells has become commercially available very recently. As the emitter dopant profiles differ from the standard diffusions, a combination of process simulation and device simulation is used to predict possible applications as front emitter. The simulations show that ion energies of 10 to 30 keV and doses in the range of 5×1014 to 7×1015 cm-2 are sufficient for reducing the phosphorus peak density and, hence, obtaining cell efficiency levels above 20%, if appropriate surface passivation and wafer materials are used. The simulations strongly indicate, however, that cell efficiency improves only marginally if the cell has a fully metallized rear Al-BSF and a boron-doped Cz base in the degraded state. Simulated cells with a local rear Al-BSF show an efficiency improvement of more than 0.3% absolute in the degraded state

Tracking spectral shapes and temporal dynamics along a femtosecond filament

The spectral evolution of a high-intensity light channel formed by filamentation is investigated in a detailed experimental study. We also track the spatio-temporal dynamics by high-order harmonic generation along the filament. Both the spectral and temporal diagnostics are performed as a function of propagation distance, by extracting the light pulses directly from the hot filament core into vacuum via pinholes that terminate the nonlinear propagation. We compare the measured spectral shapes to simulations and analyze numerically the temporal dynamics inside the filament. © 2011 Optical Society of America

Loss analysis and improvements of industrially fabricated Cz-Si solar cells by means of process and device simulations

We model currently fabricated industrial-type screen-printed boron-doped Cz silicon solar cells using a combination of process and device simulations. The model reproduces the experimental results precisely and allows us to predict both the efficiency gain after specific cell improvements and the associated thermal budgets. Separating the resistive losses (evaluated for various contributions) from the recombination losses (evaluated in different device regions) allows us to forecast the improvements of the emitter and the rear side necessary such that the recombination losses in the base dominate. We predict that to increase cell efficiency considerably beyond 19.7 %, the base material needs to be improved

Deterministic polarization chaos from a laser diode

Fifty years after the invention of the laser diode and fourty years after the report of the butterfly effect - i.e. the unpredictability of deterministic chaos, it is said that a laser diode behaves like a damped nonlinear oscillator. Hence no chaos can be generated unless with additional forcing or parameter modulation. Here we report the first counter-example of a free-running laser diode generating chaos. The underlying physics is a nonlinear coupling between two elliptically polarized modes in a vertical-cavity surface-emitting laser. We identify chaos in experimental time-series and show theoretically the bifurcations leading to single- and double-scroll attractors with characteristics similar to Lorenz chaos. The reported polarization chaos resembles at first sight a noise-driven mode hopping but shows opposite statistical properties. Our findings open up new research areas that combine the high speed performances of microcavity lasers with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure

Phase matching of high-order harmonics in a semi-infinite gas cell

Phase matching of high-order harmonic generation is investigated experimentally for various parameters in a semi-infinite gas-cell (SIGC) geometry. The optimized harmonic yield is identified using two different noble gases (Xe and He) and its parameter dependence is studied in a systematic way. Beside the straightforward setup of the SIGC, this geometry promises a high photon flux due to a large interaction region. Moreover, since the experimental parameters within this cell are known accurately, direct comparison to simulations is performed. Spectral splitting and blueshift of high-order harmonics are observed. © 2009 The American Physical Society