Comparison of multilayer laser scribing of thin film solar cells with femto, pico and nanosecond pulse durations

We report experimental studies on laser scribing of thin film solar cells using various types of short pulsed lasers (nanosecond, picosecond, and femtosecond temporal pulse widths), aiming to determine the optimum laser parameters for the scribing of multilayer structures of amorphous silicon (a-Si) and copper indium diselenide (CIS) based solar cells. Detailed laser scribing parameters such as repetition rate of the laser pulses, scanning speed of the sample and laser beam, individual pulse energy, laser wavelength, and direction of laser illumination (either from film side or from substrate side) are examined. Characteristics of each scribing conditions are evaluated in terms of morphology by atomic force microscopy (AFM) and scanning electron microscopy (SEM), chemical species analysis by Energy Dispersive Xray Spectroscopy (EDS), and electrical conductance of interconnects by conductive AFM (c-AFM) and contact resistance measurement to determine the optimal laser scribing conditions. Further issues on defects in the films such as re-deposited debris, elevated molten rim and delamination, thermal damage to surrounding and/or underlying layers and inter-diffusion of materials at the interface are discussed on the basis of thermal/mass diffusion, thermal stress, and ablation-induced plasma formation, in order to demonstrate an efficient laser scribing of P1/P2/P3 of thin film solar cells.