The project SIFORCE (Silicon Improvement FOR higher Cell Efficiency) is led by Prof. Luciano Mule’ Stagno and Dr Ing. Marija Demicoli at the Institute for Sustainable Energy (ISE) at the University of Malta. The research support officer Dr Jinta Mathew is the main researcher working on this project at ISE. The project is also being carried out in collaboration with the Middle East Technical University Centre for Solar Energy Research and Applications (ODTÜ-GÜNAM), led by Prof. Dr. Raşit Turan, and the industrial partner Kalyon PV, led by Nurhayat Yildirim.
The aim of the project is to acquire new knowledge and skills concerning the effects of defect generation and growth mechanisms in commercial silicon crystals on the performance of high-end solar cells. Single-crystal silicon accounts for most of the solar capacity installed worldwide, with the efficiency of the top-performing solar panels currently ranging between 21%-22%. Improving the efficiency of silicon-based solar cells is imperative to harness solar power to its fullest extent. The current improvements in efficiency were attained by better manufacturing techniques and purer materials. It is however known that the so-called grown-in defects in silicon have a direct impact on cell efficiency and that crystal engineering is required to stop or reduce the defect growth rate in silicon wafers.
Throughout its first year, the project succeeded in growing material (silicon crystals) at Kalyon PV, leading to the availability of samples with different growth profiles. This was crucial to meet the objectives of the project as it enabled a comparison of the efficiencies achieved from solar cells built on silicon wafers from different parts of the crystal. Detailed polishing procedures were developed at ISE to ensure that these samples have a specular surface which is required for subsequent good material characterisation. Pre-cell material characterisation was carried out to investigate important parameters such as the range of oxygen and defect size/density using various tools at the Solar Research Laboratory. Such tools and techniques include Laser Scattering Tomography, Fourier Transform Infrared Spectroscopy, Photoluminescence Imaging and Lifetime. Solar cells were then fabricated on the characterised wafers at ODTÜ-GÜNAM with initial results indicating no immediate relation between solar cell efficiency and defect density. These results were presented at the SiliconPV Conference held in Chambery, France in April 2024.
Such results led the research team into the second stage of the project during which silicon wafers were engineered through heat treatment to mirror the grown-in material with various defect densities. Our partner ODTÜ-GÜNAM is currently fabricating solar cells on these characterised silicon wafers to quantify the solar cell yield. Such an approach will enable the development of a more evident correlation between defect density and solar cell efficiency. Such results will be eye-opening to the relevant industries and will attract considerable interest and further future funding and collaboration.
Project SIFORCE is financed by the Energy and Water Agency under the National Strategy for Research and Innovation in Energy and Water (2021-2030).