Conformally flat black holes in Poincar\'e gauge theory

General criteria for the existence of conformally flat Riemannian solutions in 3D Poincar\'e gauge theory without matter are formulated. Using these criteria, we show that the Oliva-Tempo-Troncoso black hole, a solution of the Bergshoeff-Hohm-Town\-send gravity, is also an exact vacuum solution of the Poincar\'e gauge theory. The related conserved charges, calculated from the Hamiltonian boundary term, are shown to satisfy the first law of black hole thermodynamics. The form of the boundary term is verified by using the covariant Hamiltonian approach.