The mass spectrum of stellar black holes (BHs) is highly uncertain. Theoretical models of BH formation strongly depend on the efficiency of stellar winds of the progenitor stars and on the supernova (SN) explosion mechanism. We discuss the BH mass spectrum we obtain using SEVN, a new public population-synthesis code that includes up-to-date stellar-wind prescriptions and several SN explosion models. Our models have been used by the LIGO and Virgo collaboration to constrain the properties of the gravitational wave (GW) source GW150914, indicating a sub-solar metallicity environment for its progenitors. We show that our models predict substantially larger BH masses (up to ∼ 100 M) than other population synthesis codes, at low metallicity. In this proceeding, we also discuss the impact of pair-instability SNe on our previously published models.
