This PDF file contains the editorial “Happy Fifth Birthday JPE!” for JPE Vol. 6 Issue 01

The influence of the laser beam profile on simultaneous wide-area crystallization and texturing of amorphous silicon (a-Si) thin films in water ambience is investigated by using a pulsed laser-beam-overlap technique. A Q-switched Nd³+:YAG laser with the second harmonic wavelength of 532 nm and different beam profiles, namely Gaussian and flat-top, was used for the annealing of 1-μm thick a-Si films deposited on crystalline silicon (c-Si) substrates. High density and smaller-sized conical spikes with an increase in grain size of around 25% and improved photoconductivity characteristics (9% to 17%) were observed after laser treatment was carried out in water when compared with that in air. Further, crystalline characteristics were also improved with the flat-top beam profile as compared with that of the Gaussian beam profile. The necessary laser fluence range based on the thermal modeling in the underwater ambience is in good agreement with the experimentally measured values between 150 and 600  mJ/cm². The improvement in morphological, crystalline, and electrical characteristics of a-Si films clearly show that underwater annealing and texturing with the Nd³+:YAG laser beam-overlap of 30% to 50% is suitable for photovoltaic applications.

Using drift-diffusion simulations, we have clarified the effect of two-dimensional lamellar ordering on the device performance and, in particular, the open circuit voltage in donor–acceptor type organic solar cells. The simulations are performed both in systems where direct (band-to-band) recombination dominates and in systems where trap-assisted recombination dominates. Results show that lamellar ordering reduces both the amount of direct and trap-assisted recombination, which is beneficial for device performance. The effect is particularly prominent for small lamellar thicknesses (∼1  nm). It is furthermore shown that in the case of s-shaped current–voltage characteristics due to electrostatic injection barriers the s-shape becomes less prominent for thinner lamellar thicknesses.

An overview of the measurement techniques and results of studies on the stability of copper indium gallium selenide (CIGS) solar cells and their individual layers in the presence of atmospheric species is presented: in these studies, Cu(In,Ga)Se₂ solar cells, their molybdenum back contact, and their ZnO:Al front contact were exposed to liquid water purged with gases from the atmosphere, like carbon dioxide (CO₂), oxygen (O₂), nitrogen (N₂), and air. The samples were analyzed before, during, and after exposure in order to define their stability under these conditions. The complete CIGS solar cells as well as the ZnO:Al front contact degraded rapidly when exposed to H₂O combined with CO₂, while they were relatively stable in H₂O purged with O₂ or N₂. This was caused by either degradation of the grain boundaries in the ZnO:Al film or by the dissolution of part of this film. Uncovered molybdenum films, on the other hand, oxidized rapidly in the presence of H₂O and O₂, while they were more stable in the presence of H₂O with N₂ and/or CO₂.