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Improved c-Si Cell Performance Through Metallizations Adapted to Reduce Recombination Effects

By Giovanna Laudisio, Peter J. Willmott, Michael Rose, Richard J. S. Young


ABSTRACT
The solar conversion efficiency of photovoltaic cells is affected by recombination effects. SiNx, SiO­2 or other passivation layers deposited on the front side of the solar cells act as both anti-reflective coating and as passivation layer to prevent recombination effects. The removal of this layer during firing to allow electrical contact between the cell and the electrode reduces its passivation effect, thereby decreasing the Voc and the overall efficiency of the cell. Screen-printed metallization pastes are widely used in the PV industry to form contacts on the surface of silicon solar cell. While contact between fingers and emitter is essential to recover electrical current from the cell, the removal of the passivation layer under the busbars is undesirable because the area of the emitter under the busbars does not contribute to electron-hole production.

In current production lines, the front side metal grid is commonly applied using a pattern, known as H pattern, which consists of narrow finger lines and two or three wide busbars lines at a right angle. Fingers are designed to achieve low series resistance while keeping low metal coverage. Busbars provide good adhesion for the tabbing ribbons connecting the cells in the module.

This paper presents a novel approach based on decoupling the screen printing of fingers and busbars allowing the optimization of the metallization pastes for each features of the front side grid. This work reports the performance of a paste specially designed for busbars which provides excellent adhesion properties, increased conductivity and higher Voc by improving the passivation effect of the ARC layer.

Results show that a efficiency increase of 0.2% absolute can be achieved using this paste designed specifically for decoupled busbars compared to a single print H pattern.

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