Ultrafast, deep-dopant diffusion in crystalline silicon by laser-induced full area surface melting

Published: November 01, 2018

Author(s)

Zibo Zhou, Ivan Perez-Wurfl, Brian J. Simonds

Abstract

As solar cell back contact schemes have improved in recent years, the non-ideal emitter region has become a dominant contributor to overall losses in solar cell efficiency. Our analysis shows that these losses can be greatly reduced by creating a lightly (<1018 cm-3), uniformly doped emitter that is about 10 µm deep. However, the constraints imposed by current manufacturing techniques, namely using a tube-furnace for solid state dopant diffusion, limits the emitter to a much more highly doped (~1020 cm-3) and shallow (< 500 nm) region. A laser- based process by which dopants are diffused in a liquid silicon state can overcome these limitations. In this work, we provide semiconductor device simulations that compare the effects of these two types of emitters on device performance. Then, we used a heat transport model to demonstrate that a focused laser line beam can create a molten region at the surface of a silicon wafer that would allow dopants to diffuse deeply within a short amount of time. We then performed the laser processing with a scanned laser line beam on preheated silicon samples. The resulting junction depth (>10 µm) is measured by cross-sectional etching and electron beam- induced current measurements. Electrochemical capacitance-voltage measurements are used to measure both the depth as well as the dopant profile resulting from the laser-driven process. A simple solar cell device is created and its performance is discussed. In order to understand the causes limiting cell performance, we analyse dislocation defects induced by the large thermal gradients inherent to the laser-based process.
Citation: Journal of Solar Energy Materials and Solar Devices
Volume: 86
Pub Type: Journals

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Keywords

Laser Processing, Solar Cells, Silicon
Created November 01, 2018, Updated September 27, 2018