Stella Yu : Publications

Deep Learning Approach to Inline Quality Rating and Mapping of Multi-crystalline Si-wafers
Matthias Demant and Patrick Virtue and Aditya Kovvali and Stella X. Yu and Stefan Rein
European Photovoltaic Solar Energy Conference, Brussels, Belgium, 24-28 September 2018
Paper

Abstract
This work shows the first successful application of CNNs for material characterization and process control in solar cell production. We present a fully data-driven machine learning approach for inline quality rating and quality mapping of as-cut multi-crystalline Silicon (mc-Si) wafers. We use Photoluminescence (PL) images to image crystallization related defects in the wafers. We show that we can learn how to quantify these defect patterns based on empirical data and derive a meaningful wafer representation directly from the high-resolution input images by means of deep convolutional neural networks (CNN). This end-to-end regression model predicts solar cell efficiencies with mean errors of 0.12\% for materials of bricks not presented in the training set, which is 25\%rel better than our classical methods based on feature engineering. Moreover, we visualize the expected quality distribution for each sample within a spatially resolved activation map. The mapping procedure gives an insight into the “black box” neural network and shows that the quality distribution is in accordance to the expectations of domain experts and similar to spatially resolved quality data like the image of the dark saturation current density (j0). More details on learning and mapping will be reported within two studies elsewhere.

Keywords
multi-crystalline silicon, convolutional neural networks, regression activation mapping, material rating, semantic representation, PERC