Tuning quantum-dot heat engines for optimal ecological performance

We study the performance of electron-based quantum-dot heat engines using non-equilibrium thermodynamics and optimize them using an ecological performance criterion. We first globally optimize the system, assuming that we can control both the gate and drain voltages simultaneously. We then show that less general optimizations are possible, in which we control only the drain voltage. In the final part of the paper, we demonstrate, using irreversible thermodynamics, a one-to-one correspondence between the extreme condition of the ecological function and the thermodynamic equilibrium condition of the system.