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Solar cells based on inorganic absorbers, such as Si, GaAs, CdTe and Cu(In,Ga)Se₂, permit a high device efficiency and stability. The crystals’ three-dimensional structure means that dangling bonds inevitably exist at the grain boundaries (GBs), which significantly degrades the device performance via recombination losses. Thus, the growth of single-crystalline materials or the passivation of defects at the GBs is required to address this problem, which introduces an added processing complexity and cost. Here we report that antimony selenide (Sb₂Se₃)—a simple, non-toxic and low-cost material with an optimal solar bandgap of ∼1.1 eV—exhibits intrinsically benign GBs because of its one-dimensional crystal structure. Using a simple and fast (∼1 μm min^–1) rapid thermal evaporation process, we oriented crystal growth perpendicular to the substrate, and produced Sb₂Se₃ thin-film solar cells with a certified …