Photovoltaics via Electrodeposition of Compound Semiconductors - PECOS
Coordinating Institution:
Université du Luxembourg
Other Partner(s):
University of Utah ,
University of Bath (UK)
From: 01/01/2008
To: 31/12/2012
Budget: 800,000.00€
Contact(s):
Dale Phillip
Summary
The PECOS program is the main research project of the ATTRACT fellowship which is part of the Laboratoire Photovoltaïque headed by Prof. Susanne Siebentritt. The work of this laboratory is to investigate semiconductor materials suitable for use in solar cells which convert the energy from the sun to electrical energy. The role of the PECOS program is two fold.
Firstly to develop a new semiconductor material, kesterite, for use in a thin film solar cell by using a low cost deposition technique – electroplating, and secondly to investigate the use of a new electrodeposition medium – ionic liquids. Kesterite is a semiconductor which can be prepared in thin film form, and contains only cheap and naturally abundant materials. These properties make it an ideal candidate for achieving the goal of reducing the cost of solar cells. Electroplating is the process of depositing a thin film of conducting ions from an aqueous solution onto a metallic surface by the use of an electrical field. Normally the electroplated films must then be annealed in an oven to give the deposited material the desired properties. Ionic liquids are salts which are liquid below 100 °C and are electrically conducting. This means that they can be used instead of water in the electroplating process.
They have several advantages over water, including a very low vapor pressure at high temperature, and large electrochemical potential windows which allow the electrodeposition of elements not possible in water. It is proposed that they will replace the water in a standard electroplating process and give the deposited films enhanced properties. In the second year of the PECOS program, the fabrication of kesterite solar cells using the aqueous solution approach lead to a 3.2 % efficient device (current world record: 3.4 %). Furthermore, the deposition process and with it the thin film uniformity could be improved, however, microscopic problems, such as pinholes or multiple phases still need to be solved. The ionic liquid approach has started in 2009 and focuses on the electroplating of chalcopyrites thin films. It could successfully be demonstrated that these liquids can be used to deposit metallic gallium and gallium alloys with such high plating efficiencies that are impossible in aqueous solutions. Work in 2010 will look to understand and improve Kesterite formation processes, and aim to fabricate more homogeneous solar cell devices with larger efficiencies. The ionic liquid work will continue to focus on understanding the electrodeposition of metal alloys used as precursors for compound semiconductors.
Project Website:
Figure 1: Annealing oven used for the making of thin film semiconductors
Figure 2 : SEM image of the cross section of a Kesterite solar cell device. Glass was used as a substrate, Molybdenum (Mo) is used for the electrical back contact, MoS2 (Molybdenum sulfide) is created during the annealing process of the Kesterite (CZTS) layer. Cadmium sulfide (CdS) is used as a buffer layer between the CZTS absorber and the ZnO (Zinc Oxide) layers.