Ultrafine and High Aspect Ratio Metal Lines by Electron Beam Lithography for Silicon Solar Cell Metallisation

Ultrafine finger lines with high aspect ratio are proposed to reduce the front side metallisation losses of high-efficiency silicon wafer solar cells, as an easy-to-implement solution to boost the champion cell efficiency. The ultra-fine fingers reduce both the shading loss as well as the recombination loss at the metal interfaces, and the high aspect ratio helps to reduce the finger resistive losses. Simulation results show that fingers with width of 500 nm and height of 750 nm can reduce the overall front grid related power losses by 2.2% when applied in a 23% efficient PERL (passivated emitter and rear locally diffused) cell. To implement the ultrafine fingers, electron beam lithography is used as it can achieve excellent resolution down to 10 nm. After process optimisation, finger lines with width of 500 nm and height of 750 nm are obtained, which proves the feasibility of the proposed metallisation scheme.