Study of the Mechanical Strength Improvement of Wafers for EWT Solar Cells by Chemical Etching after the Drilling Process

Mechanical stability of EWT solar cells deteriorates when holes are created in the wafer. Nevertheless, the chemical etching after the hole generation process improves the mechanical strength by removing part of the damage produced in the drilling process. Several sets of wafers with alkaline baths of different duration have been prepared. The mechanical strength has been measured by the ring on ring bending test and the failure stresses have been obtained through a FE simulation of the test. This paper shows the comparison of these groups of wafers in order to obtain an optimum value of the decreased thickness produced by the chemical etching

Damage reduction of the laser drilling process on back contact solar cells by chemical treatment

Production of back contact solar cells requires holes generations on the wafers to keep both positive and negative contacts on the back side of the cell. This drilling process weakens the wafer mechanically due to the presence of the holes and the damage introduced during the process as microcracks. In this study, several chemical processes have been applied to drilled wafers in order to eliminate or reduce the damage generated during this fabrication step. The treatments analyzed are the followings: alkaline etching during 1, 3 and 5 minutes, acid etching for 2 and 4 minutes and texturisation. To determine mechanical strength of the samples a common mechanical study has been carried out testing the samples by the Ring on Ring bending test and obtaining the stress state in the moment of failure by FE simulation. Finally the results obtained for each treatment were fitted to a three parameter Weibull distribution