A Development of Thin Films and Laser Processes for Patterning of Textured Silicon Solar Cells

This work explores the application and optimization of laser patterning of dielectrics on textured crystalline silicon for improving the performance of industrial silicon solar cells. Current direct laser patterning processes introduce defects to the surface of the solar cell as a result of the film transparency and the intensity variation of the laser induced by the textured surface. As a means of overcoming these challenges, a co-deposited protective masking film was developed that is directly patterned with laser light at greatly depreciated light intensities that allows for selective chemical etching of the underlying dielectric films without incurring substantial defects to the surface of the device. Initial defects produced by the process are carefully evaluated with electron microscopy techniques and their mechanism for generation is identified and compensated. Further, an analysis of the opening fraction within the laser spot is evaluated –the area of removed film within the laser spot divided by the area of the laser spot– and residue produced by the laser process within the contact opening is studied. Once identified, this non-damaging laser process is a promising alternative to the standard screen print and fire process currently used by industry for metallization of silicon solar cells. Smaller contacts may be made with the laser process that are as of yet unattainable with screen printing, allowing for a decrease in shading losses. Additionally, the use of patterning allows for silver-free metallization and improved conductivity in the contacts, thereby decreasing parasitic losses in the device.