Hydrazine solution processed CuSbSe2: Temperature dependent phase and crystal orientation evolution

CuSbSe2 has attracted huge attention as an absorber material for thin-film solar cells due to its attractive optical and electrical properties, as well as earth-abundant, low-cost, and low-toxic constituent elements. However, different from the conventional inorganic absorbers such as CdTe, CuSbSe2 has a complicated phase space with at least five competitive phases such as Cu2Se, CuSe, Sb2Se3, Cu3SbSe4, and Cu3SbSe3 and crystallizes in two-dimension (2D) layered structure. Crystal phase and orientation strongly correlate with film properties and thus are crucial for device performance. In this paper, by varying the annealing temperature, we carefully investigated the phase, electrical properties and crystal orientation evolutions of hydrazine solution processed CuSbSe2 films. Intermediate Cu3SbSe3 secondary phase was identified, and the temperature dependent orientation change was observed, which is driven by the reduced surface energy, as supported by the first-principle calculations. Finally, a prototype thin film solar cell is fabricated, achieving 2.70% efficiency. Our theoretical calculation and experimental investigation demonstrated the importance of controlling phase composition and crystal orientation in the application for photovoltaics.