Transmission electron microscopy study on the laser-cutting induced microdefects in silicon heterojunction solar cells

Abstract

Silicon heterojunction (SHJ) solar cells are at the forefront of high-efficiency photovoltaic (PV) technology, achieving record efficiencies and promising bifacial performance. These cells are crucial for future PV markets, but challenges like cell-to-module (CTM) losses can reduce overall module efficiency. Half-cell module technology, using thermal laser separation (TLS), helps minimize these losses, but performance degradation persists, even with edge passivation. This study investigates how TLS affects the microstructure of SHJ cells, focusing on defects formed during laser processing. We used high-resolution scanning transmission electron microscopy (STEM) to examine these changes, providing detailed insights into the cell's structure. The results reveal that the hydrogenated amorphous silicon (α-Si:H) layer near laser-cut edges crystallizes, with the affected zones spanning approximately 12 μm at the n⁺-n junction and 6 μm at the p⁺-n junction, where the crystallization patterns are influenced by laser energy. The scribing laser also melts and diffuses the indium tin oxide (ITO) layer, and induces defects in the crystalline silicon (c-Si) regions. These changes are likely the main reasons for efficiency losses, reducing cell performance. These insights are vital for developing strategies to mitigate laser-induced defects, enhancing SHJ cell efficiency and reliability for large-scale production.