Selective removal of TCO stack layers for CdTe P1 process with a tailored pulse laser

Laser scribing has been used with great success for the CdTe P1 scribe step and a standard process sequence is well established in the industry. In particular, the common methodology for the P1 step results in exposure of the soda lime glass substrate. In turn, the Na diffusion from the glass into the film is detrimental to the performance of the CdTe solar cell (1). To mitigate this problem, commercial processes perform the P1 scribe after the CdTe deposition and the resulting groove is then backfilled with a photoresist. This photoresist application process accounts for a significant fraction of the cost for the capital equipment in a CdTe module production line. In this paper we study the impact of wavelength, pulse duration, temporal pulse shape, and film orientation on the removal dynamics of the SnO₂ film stack on TEC10 glass. We utilize a unique pulse-programmable fiber laser with the aim of developing a process that removes only SnO₂:F conductive layer from the TCO stack, leaving the underlying barrier layers intact. Achieving this result would allow the P1 scribe to be performed before the CdTe deposition and perhaps even at the time of glass manufacture thereby completely eliminating the need for the photo-resist step. We utilize optical microscopy, white light profilometry, and resistance measurements to characterize the resulting process.