Top-down Aluminum Induced Crystallization for Photovoltaics

Passivating silicon solar cell surfaces is critical to fabricating very high efficiency and low cost photovoltaic devices. The sun-facing surface of the solar cell, known as the emitter, is particularly important when designing a solar cell. This work focused first on an alternative method of forming the emitter of silicon solar cells, and secondly on a method for improving the surface passivation of both these non-traditional and standard n-type solar cells. Top-down aluminum induced crystallization (TAIC) was used for forming a polycrystalline silicon layer from amorphous silicon using aluminum to catalyze the crystallization at much lower temperatures than otherwise possible. Inherent to TAIC is the doping of the resultant crystalline silicon by the aluminum, an acceptor impurity. Thus, n-type solar cells with p-type polycrystalline emitters were fabricated. It was found that several variations of this crystallization process occurred and their effect on solar cell performance was analyzed. An inherent disadvantage to this method was the presence of defects at the junction of the highest efficiency solar cells fabricated. These defects were passivated by an atomic hydrogen treatment. Another method of improving solar cells was invented, theoretically modeled, and experimentally explored. The process improves silicon solar cells by hydrogen inactivation of acceptor impurities in the emitter (shown for both aluminum and boron in silicon). Low surface doping has been linked to lower measured surface recombination velocities for solar cell emitters with high quality dielectric passivation layers. By lowering emitter doping levels, n-type solar cell efficiencies were increased

Raman crystallinity and Hall Effect studies of microcrystalline silicon seed layers

Aluminium induced crystallization (AIC) was used to crystallize sputtered amorphous silicon thin films on aluminium‐coated glass at annealing temperatures ranging from 250‐520°C in vacuum. Crystalline volume fractions were measured by Raman spectrometry as a function of annealing temperature. It was shown that the crystallized films had large grains as the Raman peaks were centred at about 520 cm‐1 at and over annealing temperatures of 420°C. The three‐layer sample crystallization resulted in crystallization of the films at lower temperatures compared to the two‐layer sample crystallizations which implied a reduction in the cost of production of the seedlayer and resulting products. Hall mobilities and hole densities ranging from 17.0‐22.8 cm2V‐1s‐1and (4.7‐9.2) × 1018 cm‐3 respectively were measured. Low hole charge densities for films of the same thickness were achieved at high annealing temperatures which was an indication of less aluminium in seed layers prepared at those temperatures. Having seed layers with sufficiently low hole charge densities is desirable for application of the seed layer in photovoltaic applications.Key Words: microcrystalline, silicon, annealed, raman, crystallinity, hall‐effec

AlSi system influence on characteristics of power diodes

La grande variabilità del sistema Al-Si è causa di diversi problemi all’interno di linee di produzione. La stabilità, la prevedibilità, e il controllo di processi e fenomeni è una condizione cardine all’interno delle produzioni di massa che ne prevedono l’impiego. La creazione di un quadro teorico complessivo entro cui inserire i comportamenti del sistema in esame è vitale per poter raggiungere l’obiettivo di avere elevate e consistenti rese produttive