Fine front side metallisation by stretching the dispensed silver paste filament with graphite nanofibres

Abstract

The miniaturization of finger electrodes is an area of active research in the crystalline silicon solar cell industry, and diverse trials have been conducted with various printing techniques, including stencil, laser, aerosol jet, inkjet, electrohydrodynamic jet, and dispensing printing. Among these techniques, dispensing printing is regarded as promising due to its superior capability to construct fine finger electrodes with a high aspect ratio and homogeneity by single-pass printing without direct contact with the solar cell wafer. However, its requirements of a small nozzle, short stand-off distance between the nozzle and the solar cell, and specially formulated highly viscous silver paste with a high yield stress raise the issues of nozzle clogging, nozzle breakage by colliding with the solar cell, and the challenges of developing a dispensing printer that can accommodate high pneumatic pressures. In this study, a robust resolution of the aforementioned issues is proposed using graphite nanofibres. The small addition of graphite nanofibres to conventional silver paste greatly enhances the elongational property of silver paste. By stretching the silver paste filament with the enhanced elongational property, the diameter of the silver paste filament is reduced and a finger width of 47.7µm was achieved, which is finer by 21.4µm than the finger width achieved using paste without the graphite nanofibres. Moreover, the stable construction of finger electrodes is enabled with graphite nanofibres at a stand-off distance as far as 1mm and a printing speed as fast as 100mm/s. The resulting cell efficiency with graphite nanofibres is higher by +0.22%p (average) and +0.30%p (median) than those obtained without graphite nanofibres.