Investigation and Characterization of Al paste as back surface field (BSF) for High Efficiency Si Solar cell

Abstract

Photovoltaic solar cells offer many advantages, including needing little maintenance, environmentally benign of any electricity generating source with zero greenhouse gas emission. In the photovoltaic industry both the reduction of the silicon material thickness and the increase of the solar cells efficiency are critical topics for cost reduction. One key factor to reducing the cost and energy consumption of solar cell production process is reducing the thickness of the Si wafer to the order of 200 μm, the current industry wafer thickness ranges of 275 - 350 μm. The back-surface field (BSF), ~50 μm thick is formed during the firing of a screen printed A1 on the rear side. The main issue using thinner wafers with Al BSF is the bow of the wafers after firing. In this study, baseline Si Solar cells with 19.7% light conversion efficiencies was achieved on monocrystalline ptype CZ-Si with two types of Al BSF pastes. High performance SiN:H was grown by PECVD tool. The Al/Ag firing process for the Sun Chemical product (CTX 0435) needs to be optimized as the current process disintegrates to powder substance after Ag firing. The process window for firing the DuPont Ag front-side paste is large and yields low series resistance values without forming gas anneal (FGA anneal).