Copper Light-induced Plating Contacts with Ni Seed-layer for mc-Si Solar Cells after Laser Ablation of SiNx:H

Abstract

This study focuses on the electrochemical Ni/Cu metallization of multi-crystalline silicon (mc-Si) without alignment steps. Selective ablation of the silicon nitride (SiNx:H) anti-reflection and passivation coating was performed prior to metallization with a frequency tripled Nd:YAG laser. Electroless nickel-phosphorous layers of different thicknesses were deposited as a seed-layer at 95°C on two batches of samples before electrolytic copper thickening. The thickening of the Ni contact by copper was done by light-induced plating (LIP). The influence of laser ablation parameters as well as chemical etching prior to metal deposition was investigated. The morphology of electrochemically deposited Ni and Cu metal layers was investigated by SEM and optical microscope. Laboratory scale solar cells were fabricated to evaluate the electrical properties of the front contacts. A copper thickness of between 9 and 16μm was necessary in order to optimize the fill factor. The best efficiency measured on 200μm thick p-type mc-Si solar cell with an area of 4.4cm2 was 15.5%. An average efficiency of 15% over 18 samples has been demonstrated. Such results were obtained without any additional thermal annealing treatment of the Ni seed-layer. The limiting factors as well as possible improvements are discussed.