The Investigation of Tin Sulfide Solar Cells by Sputtering and Sulfurization

In the last few years, thin film solar cells draw people’s attention due to their great potential application in the future, especially for CIGS and CdTe solar cells. Despite the promise of these technologies, restrictions on heavy metal usage for Cd and limitations in supply for In and Te are projected to restrict the production capacity of the existing chalcogen-based technologies to ＜100GWp per year, a small fraction of our growing energy needs, which are expected to double to 27TW by 2050. Earth-abundant tin-base materials, Cu2ZnSnS4, have been proposed as potential alternatives for the future technologies. However, Cu2ZnSnS4 has a problem of narrow stability range of this multi-component material. Therefore, simpler binary Earth-abundant absorbers have recently experienced a renewed interest in the PV community. SnS is a potential photovoltaic absorber because of its high optical absorption coefficients ~105cm-1, non-toxic p-type semiconductor with a bandgap of 1.3eV, which is close to the optimal bandgap, etc. Therefore, SnS will be investigated in this project. This project will be implemented by two years. In the first year, material properties of SnS will be investigated. The SnS thin film will be deposited by sputtering and sulfurization techniques. Two methods, sputtering SnS thin film directly and sputtering Sn and then sulfurization, are compared to prepare SnS thin film. A good quality of SnS thin film is obtained by adjusting sputter parameters, such as RF power, pressure and substrate temperature, and then high-temperature annealing treatment. For sulfurization process, the temperature, time and sulfur vapor are carefully controlled, especially for observing the high or low sulfur vapor related to the formation quality of SnS thin film. In literature, it is known that sulfurization technique can produce a large-grain SnS thin film. In the second year, a high efficiency SnS solar cell device is fabricated by suitably choosing a buffer layer material, such as CdS、ZnS、ZnO and SnS2, etc. These buffer layers will be prepared by chemical bath deposition, not by sputtering technique, to obtain a good interface property. The energy band offset at the buffer/absorber heterojunction, like a spike or cliff, is very important for making a high efficiency solar cell. From our preliminary simulation results, a good solar efficiency can be obtained by choosing CdS or ZnO as a buffer layer. In this work, the fabricating solar cell structure will be determined by our simulation results and verified by device measurement. Based on our past experiences for making CIGS and CZTS solar cells, I hope we can make the highest efficiency of SnS solar cells in the world.

Project ID:PB10207-1805
External Project ID:NSC102-2221-E182-041