We investigate the power losses in back-contact back-junction monocrystalline thin-film silicon solar cells. The cells are made from epitaxial layers grown on and separated from porous Si (PSI process). We combine two-dimensional finite element modeling with a resistance network simulation. The simulated and measured current-voltage characteristics agree. Free energy loss analysis reveals that the main limiting loss mechanism of the best cell with 13.5 % efficiency is the high saturation current density at the metal-silicon interface of 5×104 fA cm2, causing 2.5 % absolute efficiency loss.

Fast laser processing is commonly done using a Gaussian laser beam in combination with a scanner. Single laser pulses only affect a limited area beneath the Gaussian intensity bell and result in circular impact regions. Adjacent impact regions have to overlap when continuous processing larger areas. Thus, the processing speed is greatly enhanced by replacing the Gaussian profile with a flat-top intensity profile and by replacing the radial symmetric cross section with a rectangular cross section. However, processing with a rectangular flat-top laser beam through a scanner has, to the best of our knowledge, not yet been demonstrated. We report on the successful design and experimental tests of a new laser system that images a rectangular flat-top profile through a scanner. Our so-called Simultaneous Scanning and Laser Beam Imaging - system (SIMSALABIM) machines a finger pattern that covers 50% of a (125 × 125) mm 2 crystalline Si solar cell in 14 s. Two parallel systems with increased output power should process the same area in just 2.5 s.

We use laser ablation of Si and laser ablation of organic coatings on Si wafers for locally processing solar cells. We present experimental investigations of a variety of pulsed lasers, such as Nd:YAG laser and frequency-converted solid state lasers concerning their applicability of laser structuring silicon solar cells. The laser-induced Si crystal damage is investigated by means of contact-less minority carrier lifetime measurements. With our optimized laser parameters for structuring monocristalline Si we find the depth of the laser-induced damage to be 3 µm for the frequency-tripled (λ = 355 nm), 4 µm for the frequency-doubled (λ = 532 nm), and above 20 µm for the Nd:YAG (λ = 1064 nm) laser. One-dimensional simulation results show the influence of a lowered minority carrier lifetime in the silicon absorber on the performance of a back junction solar cell. With an optimized laser process we fabricate solar cells with a Rear Interdigitated contact scheme that is metallized by one Single vacuum Evaporation step (RISE). The so-called RISE process aims at highest efficiencies in combination with low process complexity.