We have measured the electrical resistivity and thermopower of electron-doped perovskite cobaltites ${\mathrm{LaCo}}_{1\ensuremath{-}y}{\mathrm{Te}}_{y}{\mathrm{O}}_{3}$. In contrast to hole-doped systems such as metallic ferromagnets ${\mathrm{La}}_{1\ensuremath{-}x}{M}_{x}{\mathrm{CoO}}_{3}$ $(M=\text{Ca}, \mathrm{Sr}, \mathrm{Ba})$, the electron-doped samples show an insulating behavior even in a heavily doped range due to a spin-state blockade mechanism that an electron hopping from a high-spin ${\mathrm{Co}}^{2+}$ to low-spin ${\mathrm{Co}}^{3+}$ site is energetically suppressed. We find that, despite electron doping, the thermopower shows relatively large positive values above $y=0.05$, strikingly distinct from the hole-doped case where it comes close to zero with doping. This prominent electron-hole asymmetry seen in the thermopower originates from a bipolar conduction which consists of a slight number of mobile holes and the main immobile electrons, demonstrating the impact of a spin-state blockade on thermoelectric transport.