Widespread application of photovoltaic power to provide a significant fraction of the world’s energy needs will require a dramatic lowering of photovoltaic cell material cost and thus, the use of inexpensive, abundant materials and low-cost fabrication strategies. One candidate material that has the potential to meet these requirements is Cu2ZnSnS4 (CZTS). CZTS has a favorable band gap for solar cell applications, is made entirely of abundant materials and has a high absorption coefficient to minimize the quantity of material used in devices.
In order to prepare thin films of CZTS we constructed a five target sputtering system. The system consists of a load lock for rapid sample loading/unloading, a large chamber with three sputter guns for co-deposition of copper, zinc and tin, and a secondary chamber for deposition of chromium and molybdenum to be used as back contacts for CZTS devices. It includes a substrate heater for temperature control from room temperature up to 700°C and a rate monitor to control deposition rate. We also added a H2S gas source in an attempt to incorporate sulfur into the films during the deposition process. By introducing controlled quantities of H2S into the sputtering ambient we can reactively sputter a CZTS film with the required crystal structure in a one-step process. This process has the potential to eliminate the defects associated with out-diffusion of metals during the post-deposition H2S anneal used in the current world record process.
Students: Chinmay Nivargi