Abstract Barium disilicide (BaSi 2 ), composed of Earth-abundant and nontoxic elements, is a promising material for thin-film solar cells. The control of carrier type and carrier concentration by impurity doping is particularly important for the application of BaSi 2 to solar cells. However, the presence of defects in semiconductors such as BaSi 2 may have a significant impact on the electrical and optical properties of solar cells. In this study, we chose boron to act as a p-type impurity in BaSi 2 and studied boron-related defects using the Quantum Espresso method with density functional theory. The formation energy of interstitial boron defects was found to be lower than that of boron in Si vacancy sites. The hyperfine coupling constants of 137 Ba with antisite boron defects (B Si ) are very localized and differ significantly from those of 137 Ba with interstitial boron defects (B i ). This suggests that neutral B Si and B i can be identified by electron paramagnetic resonance.