3D TEM characterization of silver implanted silicon for intermediate band solar cells

Abstract

As the need for renewable and sustainable energy sources are growing solar cells are turning into one of the most affordable and widely adopted solutions for renewable electricity production. This is driven by a steady increase the solar cell efficiency and a reduction of cost. Today production solar cells are approaching the theoretical limit of of today's technology and soon further improvement must come from alternative technologies.

The intermediate band solar cells is one such candidate. The issue is that intermediate band materials have not been found naturally and need to be made. As a candidate for an intermediate band material silver implanted silicon have been made by ion implantation and pulsed laser melting in previous work at NTNU.

In this master thesis silver implanted silicon is characterized by different TEM techniques to see how silver is distributed in the silicon. This is done by cross section TEM. Silver were found to segregates in complex 3D structures and 3D characterisation were needed to understand them.

Electron tomography is a technique for 3D characterization in TEM. There was no work flow available for electron tomography on the microscopes at NTNU so this had to be developed. As this work flow have extensive use outside of the thesis the tomography work flow development is a goal in it self.

Electron tomography is demonstrated trough a work flow for acquisition on the NORTEM microscopes at NTNU and processing mainly in python and other open source software. From the 3D data the segregated silver were found to make up very different features for different processing parameters.

To summarize this thesis cover two topics. Silver implanted silicon have been characterized with 2D and 3D TEM techniques. Secondly a work flow for electron tomography is demonstrated.