Development of Earth-Abundant Tin(II) Sulfide Thin-Film Solar Cells by Vapor Deposition.

摘要

To sustain future civilization, the development of alternative clean-energy technologies to replace fossil fuels has become one of the most crucial and challenging problems of the last few decades. The thin film solar cell is one of the major photovoltaic technologies that is promising for renewable energy. The current commercial thin film PV technologies are based on Cu(In,Ga)Se 2 and CdTe. Despite their success in reducing the module cost below ;Because of the high volatility of sulfur and various oxidation states of tin, non-stoichiometric chemical composition, traces of other phases (i.e. Sn, Sn2S3, and SnS2), and elemental impurities (e.g. oxygen) are usually observed in SnS films obtained from various reported deposition techniques. First, we present a process to prepare pure, stoichiometric, single-phase SnS films from atomic layer deposition (ALD). The as-deposited SnS films exhibit several attractive properties, including suitable energy band gaps (Eg,~ 1.1 - 1.3 eV), a large absorption coefficient (alpha > 104 cm-1), and a proper carrier concentration ([p] ~ 1015 - 10 16 cm-3). Then, heterojunction solar cells were fabricated from p-type SnS and n-type zinc oxysulfide (Zn(O,S)). A record high active-area efficiency of 2.46 % was achieved via conduction band offset engineering by varying the oxygen-to-sulfur ratio in Zn(O,S).;Finally, we address two approaches potentially used for improving a device efficiency of the SnS solar cell. First, via doping to create an n-type SnS, a p-n homojunction device could be made. We present the processes and the results of doping SnS films with antimony and chlorine, potential n-type dopants. Second, by post-deposition heat treatment, an improvement in the transport properties of SnS film can be achieved. We discuss the effect of temperature and an annealing ambient (N2, H2S, and sulfur) on grain growth and the electrical properties of annealed SnS films.