Record High Efficiency Screen-Printed Belt Co-Fired Cells on Cast Multi-Crystalline Silicon

Presented at the 19th European Photovoltaic Solar Energy Conference and Exhibition, Paris, France; June 7-11, 2004.Record-high efficiency screen-printed 4 cm(2) solar cells were achieved on HEM and Baysix cast multi-crystalline silicon. These cells were fabricated using a simple, manufacturable process involving POCl3 diffusion for a 45 Ω/ ٱ emitter, PECVD SiN(x):H deposition for a single-layer antireflection coating and rapid co-firing of an Ag grid, an Al back contact, and Al-BSF formation in a belt furnace. This process scheme resulted in effective impurity gettering and defect passivation. It also contributed to good ohmic contacts with series resistance of < 1Ω-cm(2), back surface recombination velocity of < 500 cm(2)/s, high average bulk lifetimes in the range of 100-250 μs after cell processing and fill factors of ~0.78. These parameters resulted in record high, 16.9% and 16.8% efficient screen-printed cells on HEM (Heat Exchanger Method) and Baysix mc-Si (confirmed by NREL). The identical process applied to the un-textured Float zone (FZ) wafers gave an efficiency of 17.2%. The optimized co-firing cycle, when applied to HEM mc-Si wafers with starting lifetimes varying over a wide range from 4 - 70 μs, resulted in a very tight efficiency range of 16.6% to 16.8% as a result of efficient defect gettering and passivation. Model calculations performed using the simple cell design and measured cell parameters agreed well with the experimental cell efficiency

Design of a High-Throughput Plasma-Processing System

Sandia National Laboratories has demonstrated significant performance gains in crystalline silicon solar cell technology through the use of plasma-processing for the deposition of silicon nitride by Plasma Enhanced Chemical Vapor Deposition (PECVD), plasma-hydrogenation of the nitride layer, and reactive-ion etching of the silicon surface prior to the deposition to decrease the reflectivity of the surface. One of the major problems of implementing plasma processing into a cell production line is the batch configuration and/or low throughput of the systems currently available. This report describes the concept of a new in-line plasma processing system that could meet the industrial requirements for a high-throughput and cost effective solution for mass production of solar cells