Photovoltaic conversion of solar energy into electricity is an alternative way to use renewable energy for sustainable energy production. The great demand of low-cost and efficient solar cells inspires research on solution-processable light-harvesting materials. Antimony trisulfide (Sb 2 S 3) is a promising light-harvester for photovoltaic purposes. Here we report on the in situ grown monolayer of preferentially oriented, large Sb 2 S 3 single-crystalline cuboids on a polycrystalline titania (TiO 2) nanoparticle film. A facile, oriented seed-assisted solutionprocessing method is used, providing the Sb 2 S 3 /TiO 2-based bulk/nano-planar heterojunction with a preferred structure for efficient planar solar cells. An orientation-competing-epitaxial nucleation/growth mechanism is proposed for understanding the growth of the Sb 2 S 3 singlecrystalline cuboids. With an organic hole transporting material, the stable solar cell of the heterojunction yields a power conversion efficiency of 5.15% (certified as 5.12%). It is found that the [221]-oriented Sb 2 S 3 cuboids provide highly effective charge transport channels inside the Sb 2 S 3 layer.

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