Recovery of LeTID by low intensity illumination : reaction kinetics, completeness and threshold temperature

Light (and elevated Temperature) Induced Degradation (LeTID) can seriously limit the efficiency of mc-Si PERC solar cells if no countermeasures are taken. Within this paper, the subsequent regeneration reaction, also induced by light at elevated temperatures, is investigated systematically in the low intensity regime (up to 4 suns) as a possible countermeasure. As might be expectable, degradation and regeneration reaction are found to speed up with increasing treatment temperature; however, completeness of regeneration is also found to be noticeably reduced at high temperatures (up to 380°C). This enforces the introduction of reverse reactions and gives rise to a 3-state reaction model for LeTID explaining the observed threshold temperature above which LeTID elimination does not work anymore. Furthermore, it is found that a treatment at high temperatures not only fails to eliminate LeTID, but also slows down the regeneration in a later low temperature treatment.publishe

Comparison of different feedback modalities for the training of procedural skills in Oral and maxillofacial surgery: a blinded, randomized and controlled study

Background The feedback given to students plays an important role in their efficiency related to learning practical skills. In the present study, diverse feedback modalities have been investigated. Our hypothesis is that individualized and unsupervised video feedback can produce a similar learning experience as performing practical skills in an oral and maxillofacial surgery setting with conventional direct expert feedback (control group). Methods This prospective, randomized, controlled, and blinded study compared direct expert feedback (DEF), individualized video feedback (IVF) and unsupervised video feedback (UVF). The participants were fourth-year dental students from University Goethe in Frankfurt. The students were assigned to one of the three feedback methods (n = 20 per group) using simple randomization. All participants watched an instruction video for an interdental (‘Ernst’) ligature and periphery venous catheterization. Next, the students were video recorded performing the tasks by themselves (pre-test). Following this, every student received feedback using one of the above-mentioned feedback modalities. The participants then performed the same task again while being video recorded (post-test) to measure the acquired competence. Six weeks later, the students participated in an objective structured clinical examination (OSCE) to evaluate their long-term knowledge retention. All examiners were blinded regarding the students’ instructional approach and their affiliation in terms of the learning group. Results For the interdental ligature, we found significant improvements in performance in each feedback modality group between the pre-test and post-test (p < 0.001). UVF had the strongest effect on performance time. The comparison between each group in the post-test showed no significant differences between the three groups. Conclusion This study showed that IVF and UVF can be considered an alternative or adjunct to conventional methods (i.e. DEF) when learning procedural skills in oral and maxillofacial surgery. However, DEF showed to be the most effective method of feedback and therefore preferable in teaching

Influence of Al Particle Size and Firing Profile on Void Formation in Rear Local Contacts of Silicon Solar Cells

In this paper, the influence of Al particle size and the applied firing profile on void formation in local rear contacts of wafer-based silicon solar cells is investigated. Samples with a passivated emitter and rear cell (PERC) rear, but without front metallization, were metalized with six different Al screen-printing pastes, i.e., both commercial and homemade, featuring different particle size distributions and fired in a rapid thermal processing furnace with different firing profiles. Voids were detected with scanning acoustic microscopy measurements, and the fraction of voids in rear local contacts was analyzed. It was shown that the heating phase of the firing process has the strongest influence on void formation. With slower heating, void formation could be reduced to a fraction lower than 5% of the local contact area. Furthermore, it was shown that Al pastes consisting of a mixture of small and large Al particle sizes have a positive effect on the formation of voids.publishe