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We present a detailed study on incomplete ionization (i.i.) of aluminum acceptors in highly aluminum-doped p+ silicon formed by alloying from screen-printed Al pastes. We apply electrochemical capacitance-voltage (ECV) and secondary ion mass spectrometry (SIMS) measurements to detect the Al doping profiles and discuss key aspects necessary for a precise determination of the profiles. The excellent accordance of ECV- and SIMS-measured acceptor profile curves allows for the accurate investigation of Al acceptor ionization. We review the physics of i.i. and verify a simple quantitative model for incomplete Al acceptor ionization by comparing measured and calculated sheet-resistances of Al-doped p+ Si surfaces. We thus show that the electrically active Al doping concentration is nearly two times lower than the total Al concentration, so that i.i. of Al acceptors has to be considered for the correct description of highly Al-doped p+ Si regions. Therefore, our results allow for an improved quantitative analysis of n- and p-type silicon solar cells with Al-alloyed p+ rear emitter or back surface field, respectively. [ABSTRACT FROM AUTHOR]

In this study we present an advanced method for precise modeling of highly aluminum-doped p+ silicon, leading to excellent agreement of numerical and experimental data within a broad range. We analyze the influence of different recombination mechanisms on the saturation current densities of Al-doped Si surfaces for different Al profiles. Lateral doping inhomogeneities and the effect of incomplete ionization have been examined in detail. We demonstrate that incomplete ionization affects the profile characteristics significantly and, therefore, has to be accounted for in accurate modeling of highly Al-doped silicon. [ABSTRACT FROM AUTHOR]

In this paper an analytical model of the effective recombination (Seff) on the back surface of locally contacted solar cell is developed. We justify this approach by first showing that the three-dimensional (3D) problem can be reduced to a one-dimensional (1D) problem by calculating Seff. The values of Seff calculated with our model and two existing models are compared to finite element simulations. A large range of cases from high to low scale structures, including variation in the surface recombination velocity at the passivated area are investigated. The model presented in this paper is in good agreement with finite element simulations. Existing models from literature are also compared to finite element simulations, showing some of their limitations. In addition, we propose a method, not restricted to dark conditions, that simulates the 3D locally contacted structures by means of two 1D simulations. [ABSTRACT FROM AUTHOR]

Temperature-dependent lifetime spectroscopy allows for the determination of defect parameters (like ratio of the carrier capture cross sections and energy level) of pointlike defects in silicon. This necessitates reliable measurements of the low-level injection excess carrier lifetime. Photoluminescence-based measurement techniques have been shown to be ideal for this kind of measurements at room temperature, being immune to several measurement artifacts such as minority carrier trapping or depletion region modulation. In this article it will be shown how the effect of photon reabsorption influences the temperature-dependent photoluminescence measurements and how this can be accounted for using a theoretical model based on the generalized Planck equation. An intentionally titanium-contaminated silicon sample is investigated by means of temperature-dependent photoluminescence and injection-dependent photoconductance lifetime spectroscopy. Defect parameters of two independent recombination centers will be presented, which titanium introduces into the silicon band gap. One defect level at EC-0.24 eV agrees very well with a level found via deep-level transient spectroscopy measurements while another level at EC-0.49 eV could be measured for the first time using the advanced lifetime spectroscopic approach presented here. [ABSTRACT FROM AUTHOR]

In the following, high-efficiency back-contact back-junction silicon solar cells with aluminum-alloyed emitter are described. First, the theoretical background for the cell concept is explained. To that purpose, the bulk lifetime and the front surface field characteristics are considered. Three different process sequences for the phosphorus-diffused profiles on the front and back surfaces are depicted: One exhibits a shallow field, and two sequences have deeper, driven-in profiles. For realizing high efficiencies, such cell structures must meet several prerequisites, such as firing-stable front and rear passivations, and functional small screen-printed Al structures. Furthermore, it must be possible to create contacts on the Si surfaces using the driven-in P-profiles. With such a structure, cell efficiencies of 20.0% are reached. An analysis of the series resistance and area-weighted recombination is performed. The results are compared with the measured cell parameters. Two-dimensional simulations show the efficiency potential when decreasing the width of the backside field and when a cell structure, which would inhibit a passivated aluminum-alloyed p+-emitter, is created. Also, an advanced concept is demonstrated where a point array of both polarities on the cell backside is interconnected externally on module level. To that purpose, the cell is soldered to a printed wiring circuit board by using a reflow soldering process. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we present guidelines for the design of backside gratings for crystalline silicon solar cells. We use a specially developed method based on a combination of rigorous 3D wave optical simulations and detailed semiconductor device modeling. We also present experimental results of fabricated structures. Simulation-based optimizations of grating period Λ and depth d of a binary grating and calculations of the optical and electrical characteristics of solar cells with optimized gratings are shown. The investigated solar cell setup features a thickness of dbulk = 40 µm and a flat front surface. For this setup, we show a maximum increase in short-circuit current density of Δ jSC = 1.8 mA/cm² corresponding to an efficiency enhancement of 1% absolute. Furthermore, we investigate different loss mechanisms: (i) an increased rear surface recombination velocity S0,b because of an altered surface caused by the introduction of the grating and (ii) absorption in the aluminum backside reflector. We analyze the trade-off point between gain due to improved optical properties and loss due to corrupted electrical properties. We find that, increasing the efficiency by 1% absolute due to improved light trapping, the maximum tolerable recombination velocity is S0,b(max) = 5.2 × 103 cm/s. From simulations and measurements, we conclude that structuring of the aluminum backside reflector should be avoided because of parasitic absorption. Adding a dielectric buffer layer between silicon and the structured aluminum, absorption losses can be tuned. We find that for a planar reflector, the thickness of a SiO2 buffer layer should exceed [ABSTRACT FROM AUTHOR]