Deposition of CIGS absorber layer by gas flow sputtering : Initiation of project

The photovoltaic solar cell industry is growing rapidly, but high cost per watt is still an obstacle. Thin film solar cells, especially thin film solar cells using CIGS absorbers that have the highest proven efficiency, have the potential to reduce the cost through cheap manufacturing. Academic research concerning CIGS solar cells has so far been focused on cells with absorber layers deposited by co-evaporation, which can be used to make very high efficiency cells but is a deposition process ill suited for large scale production. In this thesis a process for depositing CIGS absorber layers by gas flow sputtering, a deposition technique enabling high rate depositions of low energy particles that is potentially easier to apply to a large scale production, has been outlined. Equipment for CIGS-deposition by gas flow sputtering has been prepared, characteristics of the process have been investigated and ultimately a series of first prototype CIGS absorber layers has been deposited as part of complete solar cells. A lot of focus in this thesis is on the practical work and problem solving around the equipment, e.g. pulsed DC power supplies and electrical connections, heating and heating control in a reactive vacuum environment, and on the basic functionality of the gas flow sputter, how process and film properties like deposition rate, thickness uniformity etc. vary with sputter conditions like pressure, gas flow etc. Following the process design the first prototype series produced crystalline CIGS absorbers of desired elemental composition and thickness but having rather small grain sizes, while the complete cells exhibited solar cell IV-characteristics but very poor efficiencies