An exhaustive study on the resulting impurity profile in Si samples implanted with Ti with high doses and subsequently Pulsed-Laser Melting (PLM) annealed is presented. Two different effects are shown to be present in the two different stages of the annealing. In the melting stage the box-shaped effect tends to increase the thickness of the implanted layer and to decrease the maximum peak concentration as the energy density of the annealing increases. On the contrary, in the solidifying stage, the snow-plow effect decreases the thickness of the layer and increases the maximum peak concentration as the energy density of the annealing increases. Moreover, as a direct consequence of the snow-plow effect, part of the impurities is expelled from the sample by the surface.

We applied the deactivation treatments to p-type single crystalline silicon solar cells for deactivating the recombination-active boron-oxygen complex. The methods we used include thermal annealing treatment, capacitively couple plasma (CCP) treatment, and plasma immersion ion implantation (PIII) treatment. The results showed that all the deactivation treatments were working and the energy transfer efficiency (Eff) was thereby increased by more than 1% absolute compared to the degraded state base on the increasing of the open-circular voltage (Voc) and short-current density (Jsc). The CCP deactivated treatment got better efficiencies than PIII treatment because the PIII treatment damaged the surface of solar cells. After the forming gas treatment, the samples could be improved to close to the PIII samples due to the surface damage repairing. However, the increased efficiency could not be kept and would be degraded again after illumination.

A novel method to deposit Copper Indium Gallium Diselenide (CIGS) using High Power Impulse Magnetron Sputtering (HIPIMS) was demonstrated and compared to the existing DC magnetron sputtering process. The metal-ion assisted thin-film growth inherent to a HIPIMS deposition process was used to advantage in depositing CIGS films. The HIPIMS plasma was characterized by measuring ion currents on a Langmuir probe placed into the plasma sufficiently close to the substrate. The high density plasma consisting of both metal and metal ions resulted in CIGS thin-film solar cells of superior conversion efficiencies (˜13%) as compared to conventional DC magnetron sputtering (˜10%). The efficiency enhancement was attributed to the improvement in the shunt resistance of the solar cell which corresponds to the increase in the density of the CIGS layer. Furthermore, it was also possible to grow large grained CIGS (˜1 micron) with high mobility metal-ions from the HIPIMS process. The scalability potential of the HIPIMS CIGS process was also demonstrated by running a 1.5 m long Copper-Indium-Gallium rotatable in a selenium environment using a HIPIMS power supply. The cylindrical magnetron was run at an average power of 7.8 KW and peak powers of as much as 300 KW with controlled arcing. The existence of a HIPIMS plasma was confirmed by the ion currents on the Langmuir probe and the metal signals from a Plasma Emission Monitor (PEM).

In this paper we present the structural and optical properties of Cu(In1-xGax)3Se5 ternary and quaternary compounds crystals fabricated by horizontal Bridgman technique. The Cu(In1-xGax)3Se5 materials were characterized by Energy Dispersive Spectrometry (EDS), hot point probe method, X-ray diffraction, Photoluminescence (PL), and Optical response (Photoconductivity). The Cu(In1-xGax)3Se5 have an Ordered Vacancy Chalcopyrite-type structure with lattice constants varying as a function of the x composition. A good stœchiometry given by the EDS characterization method is well observed in our samples and its magnitude deviation Δy is slight; so, our samples present a nearly perfect stœchiometry (Δy = 0) [1]. X-Ray diffraction patterns show the presence of many preferential orientations according to the planes (112), (220) and (312) of all the samples [2]. Also, it shows a linear shifting of peaks towards the higher magnitudes of 2θ when the x composition increases. These compounds can be of stanite structure [3] or an Ordered Vacancy Chalcopyrite structure (OVC) [4] or Ordered Defect Chalcopyrite Structure (ODC). We observe a large shift of the main PL and optical response emission peak versus x composition. The band gap energy of Cu(In1-xGax)3Se5 compounds is found to vary from 1.23 eV to 1.85 eV as a function of x. [1] Migual A. Contreras, Holm Wiesner, Rick Mtson, John Tuttle, Kanna Ramanathan, Rommel Noufi, Mat. Res. Soc. Symp. Proc. Vol. 426 (1996) 243-254. [2] Ariswan, G. El Haj Moussa, M. Abdelali, F. Guastavino, C. Llinares, Solid State Communications 124 (2002) 391-396. [3] M. Suzuki, T. Uenoyama, T. Wada, T. Hanada, Y. Nakamura, Jpn. J. Appl. Phys. 36 L1139 (1997). [4] Kristjan Laes, Sergei Bereznev, A. Tverjanovich, E.N. Borisov, Tiit Varema, Olga Volobujeva , Andres Öpik. Thin Solid Films 517 (2009) 2286–2290.

Solar electric (Photovoltaic) crystalline silicon (c-Si) product design and diversity has changed very little over three decades of development since the inception of the photovoltaic industry. The dominant module product comprising over 90% of cumulative installations, which exceed 15 GW worldwide, employs a ubiquitous planar laminate configuration. This paper reviews the history of development of this commodity product, and examines the scientific underpinnings of the materials base of the c-Si module platform, which has provided confidence for manufacturers to lengthen product performance warranties to the current 25 year standard. Recent trends in c-Si module design, materials and manufacturing methods will also be discussed.

Using direct photoelectrochemical measurement of the photocurrent obtained from Cu2ZnSnS4 (CZTS) absorber layers made by a two-stage electroplating-sulfurisation process, the influence of processing conditions (temperature, time, and pressure) on material quality was investigated with a view to understanding the long sulfurisation times usually found in the literature. The improvement in photocurrent due to KCN etching was also studied, and seems to be due both to removal of surface phases and also slower etching of the bulk material. The optimum sulfurisation time was found to be around 50 minutes, despite evidence that sulfur incorporation and phase formation are complete within 5 minutes. Slow grain growth was suggested as a rate-limiting factor, and a rate constant was derived based on a simple model.

This paper identifies some mechanisms that lead to problems in back Al contact formation. Major issues are related to a basic problem that the Al melt has a large surface tension and tries to ball up during the firing step. Other issues arise from dissolution of the Si-Al interface and entrapment of glass within the Si-Al alloy. Si diffusion into Al can be applied to control the melt, while cooling rate can help improve the structure of various regions of the back contact for a favorable series resistance. We also discuss a modified time-temperature profile that can lead to a deep and uniform back-surface field.

Direct electrochemical reduction of porous SiO2 pellets in molten CaCl2 salt and CaCl2-NaCl salt mixture were investigated by applying 2.8 V potential. The study focused on the effects of temperature, powder size and cathode contacting materials. Starting materials and electrolysis products were characterized by X-ray diffraction analysis and scanning electron microscopy. Due to reactive nature of silicon, different cathode contacting materials were used to test the extent of reactions between silicon produced at the cathode and the contacting materials. X-ray diffraction patterns showed that silicon produced at the cathode reacted with nickel, and iron in stainless steel to form Ni-Si and Fe-Si compounds respectively. Besides, studies revealed that higher temperature and smaller particle size had positive effects in increasing reduction rate. The results were interpreted from variation of current versus time graphs under different conditions, microstructures and compositions of the reduced pellets.

Concentration photovoltaic (CPV) systems are seen as a shortcut to achieve lower photovoltaic (PV) electricity costs/kWh. Within the available CPV configurations, V-trough systems are likely to succeed in the short term since they are less demanding in terms of tracking accuracy and due to their ability to make use of standard PV modules, a well-known and developed technology. However, silicon standard modules were initially designed to operate under 1 sun conditions, facing some challenges when integrated in CPV systems. The present work aims to demonstrate that such application is efficient up to a few suns and also to analyze possible accelerated modules degradation rates. For such analysis we have used a prototype based on the DoubleSun® technology: a 1.9x concentration V-trough system, integrating 2-axis tracking system and making use of conventional silicon modules.

We have studied the Pulsed-Laser Melting (PLM) effects on Ti implanted GaP to form an Intermediate Band (IB). Structural analysis has been carried out by means of Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), Raman spectroscopy and Glancing Incidence X-Ray Diffraction (GIXRD). After the PLM annealing, Ti concentration is over the Mott limit. Nevertheless, the Raman spectra show a forbidden TO vibrational mode of GaP. This result suggests the formation of crystalline domains with a different orientation in the annealed region regarding to the GaP unannealed substrate. This conclusion has been corroborated by GIXRD measurements. As a result of the polycrystalline lattice, a drop of the mobility is produced.

Single-wall carbon nanotubes (SWNTs) are potentially an attractive material for PV applications due to their many unique structural and electrical properties. SWNTs can be directly configured as energy conversion materials to fabricate thin-film solar cells, with nanotubes serving as both photogeneration sites and charge carriers collecting/transport layers. SWNTs can be modified into either p-type conductor through chemical doping (like thionyl chloride, or just exposure to air) or n-type conductor through polymer (like polyethylene imine) functionalization. The solar cells consist of either a semitransparent thin film of p-type nanotubes deposited on an n-type silicon wafer or a semitransparent thin film of n-type SWNT on p-type substrate to create high-density p-n heterojunctions between nanotubes and silicon substrate to favor charge separation and extract electrons and holes. The high aspect ratios and large surface area of nanotubes can be beneficial to exciton dissociation and charge carrier transport thus improving the power conversion efficiency.

The tremendous expansion and the relative avidity for silicon of the solar cell technology has resulted in a dramatic change of the polysilicon industry structure. While in the past the polysilicon was manufactured almost exclusively for the semiconductor industry, in 2008 around 67% of the total production was consumed by the solar industry. The consequence is that while in 2000 virtually only 7 companies supplied all the polysilicon consumed worldwide, in 2008 there were 11 major suppliers and numerous new ventures entering this market. Based on this in 2006 CENTESIL was founded as a new private-public partnership venture to deal with the polysilicon research. For it, a pilot plant is in advanced state of construction that has been preceded of some laboratory-size implementations. The pilot plant is designed for a production capacity of 60 kmol of trichlorosilane per day and 2 t of purified silicon per batch at the CVD reactor. The purpose is to allow the photovoltaic companies worldwide to count with an independent research centre to help them to establish their own polysilicon plant. The R&D activities already carried out by CENTESIL and the present status of the project are discussed in the paper.

Conversion efficiency of a solar energy in the electric is substantially determined not only by the total impurity concentration in solar cell element, but also by impurity chemical and physical state. Gettering processes, which are included in the technology of solar cell manufacturing, are usually used for such impurity redistribution. In order to optimize gettering processes we developed a program tool based on the fundamental physical and chemical laws. The description of physical and chemical behaviour of impurities in silicon is based both on known experimental data, and on calculations of necessary parameters by means of present-day thermodynamic and quantum-chemical methods. Developed tool helps to choose a gettering regime (a temperature profile, time, getter layer thickness) for optimization of these processes for the given initial chemical composition of the silicon wafer. Possibility of analysis of recombination activity of various types of defects in silicon on the basis of carrier lifetime criterion allows to obtain an estimation of efficiency of the gettering processes. Using this program tool we demonstrated that solar cell efficiency can be significantly increased by optimal choice of gettering conditions.

Incorporation of an electron reflector is a proposed strategy to improve the open-circuit voltage of CdTe thin-film solar cells. An electron reflector is basically a conduction-band barrier at the back surface, which can reduce the recombination resulting from the electron flow to the back surface. It should be particularly beneficial for cells with thicknesses below two microns when the CdTe absorber layer is fully depleted at its typical carrier density, because back-surface recombination is a primary limitation to the performance of fully depleted cells. Cells with thickness below two microns can also benefit from optical reflection at the back interface. One-dimension numerical simulation is used to investigate the electron reflector strategy and optical back reflection for thin CdTe cells. Theoretically, about a 200-mV increase in voltage and 3% in efficiency are achievable for a thin CdTe solar cell with 2×1014-cm-3 hole density, 1-ns lifetime, and a 0.2-eV electron reflector barrier. Furthermore, with the electron reflector, good CdTe cell performance at thicknesses as thin as 0.4 μm should be possible.

We describe a new technique for rapidly measuring average dislocation density and for mapping dislocation distribution of crystalline and multicrystalline silicon wafers. The wafer is etched in Sopori etch and the light scattered by dislocation etch pits is used to statistically count the pits. We also describe a unique arrangement for wafer illumination and measurement of scattered light that allows each dislocation map to be generated very rapidly—typically in less than 20 ms. The measurement system is now commercially available and has capabilities for measuring many other physical parameters of wafers and solar cells

We have analyzed the degree of crystalline lattice recovery in samples implanted with Ti concentrations well above the Mott limit and subsequently Pulsed-Laser Melting (PLM) annealed by means of Raman spectroscopy and Rutherford Backscattering Spectroscopy (RBS). Since very recently, theoretical studies predicted Ti interstitial sites for the Intermediate Band (IB) formation, the knowledge of the Ti impurity lattice location after PLM annealing is an essential point that can be elucidated by means of RBS measurements. After PLM annealings, Raman and RBS measurements have shown a decrease in the lattice crystalline quality as implanted dose is increased, yielding a significantly improvement of the lattice quality at the highest energy density studied. The RBS channeling spectra show that after PLM annealings Ti impurities are mostly occupying interstitial lattice sites.

Metal induced growth (MIG) was used to form epitaxial thin films of microcrystalline Si (μc-Si). By substituting Al as the catalyst metal in place of the usual Ni, x-ray diffraction (XRD) confirmed that μc-Si was successfully grown at temperatures between 350-525°C. At 525°C, a preferred orientation of (220) Si was observed with additional (111) and (311) Si orientations, while a temperature of 350°C resulted in a shift in preferred orientation to (111) Si. The lower limit for Al thickness was found to be between 10-20 nm with little crystallization and a smooth surface observed at 10 nm with XRD and SEM, respectively. Electrical measurements on Schottky diodes revealed space-charge limited conduction (SCLC) with an exponential distribution of trap levels due to diffusion of Al atoms into the Si, which was supported by analysis with energy dispersive x-ray spectroscopy (EDX) near the film surface. By depositing a thin layer of Co on top of Al prior to sputtering, the films exhibited increased crystallinity and a more uniform surface likely due to increased confinement of Al atoms. Electrical measurements demonstrated a shift from SCLC to thermionic emission in resulting Schottky diodes.

High efficiency silicon solar cells demand the use of high lifetime silicon wafers. Characterization of boules and bricks before wafering allows poor quality material to be rejected before expensive processing steps. This paper extends simulation techniques previously used in quasi-steady-state-photoconductance to transient photoconductance decay measurements of high lifetime bulk samples. Simulated photogenerated carrier density profiles allow estimation of the bulk lifetime of a thick silicon sample with high surface recombination velocity.

This study focuses on fracture properties of silicon wafers used by the photovoltaic (PV) industry as substrates for solar cells. In the first part, we numerically model three fixtures that are often used to test the strength of PV wafers. In the second part, we employ our previously developed model to predict strength of the wafers as a function of loading fixture and surface treatment. Surface treatment is simulated by removing damage from the wafer surface.