Progress with screen printed metallization of silicon solar cells - Towards 20 μm line width and 20 mg silver laydown for PERC front side contacts

Within this work, we evaluate and compare different high-end screens for the fine line front side metallization of passivated emitter and rear cell (PERC) solar cells. Three types of high-end screens are considered including (i) a fine mesh screen configuration with a mesh count MC = 520 wires/inch and standard mesh angle of φ = 22.5°, (ii) a knotless screen configuration with a mesh angle of φ = 0° as well as (iii) a knotless screen configuration utilizing a rectangular mesh with different mesh count in warp and weft direction MC = 460/430 wires/inch. Using these advanced screen configurations, all PERC solar cells are metallized with a busbarless fine line front side grid at a nominal contact finger opening of 20 μm and 24 μm. All screen configurations obtained excellent results regarding finger geometry, silver laydown and electrical performance of the front side grid and the fabricated PERC solar cells. The most efficient group obtained a printed mean finger width of 21 μm with a silver laydown of only 19 mg and revealed a mean energy conversion efficiency of 22.7%. Furthermore, we investigate the geometric and electric results of the printed front side contacts in detail using advanced image analysis software and scanning electron microscopy and discuss the impact of the fine line front side metallization on the applicable cell interconnection concepts depending on the series resistance losses.