  A three terminal nanoscale refrigeration concept based on a vibron-coupled
quantum dot hybrid system coupled to two electronic reservoirs and a phonon
bath is proposed and analyzed in detail. While investigating the non-trivial
role of electron-phonon interactions, we show that, although they are well
known to be detrimental from a general refrigeration perspective, can be
engineered to favorably improve the trade-off between the cooling power (CP)
and the coefficient-of-performance (COP). Furthermore, an additional
improvement in the trade-off can be facilitated by applying a high electronic
thermal bias. However, the allowed maximum of the thermal bias being strongly
limited by the electron-phonon coupling, in turn, determines the lowest
achievable temperature of the cooled body. It is further demonstrated that such
interactions drive a phonon flow between the dot and bath whose direction and
magnitude depend on the temperature difference between the dot and bath. To
justify its impact in optimizing the peak CP and COP, we show that a weak
coupling with the bath is preferable when the phonons relax through it and a
strong coupling is suitable in the opposite case when the phonons are extracted
from the bath. Finally, in studying the effect of asymmetry in electronic
couplings, we show that a stronger coupling is favorable with the contact whose
temperature is closer to that of the bath. Combining these aspects, we believe
that this study could offer important guidelines for a possible realization of
molecular and quantum dot thermoelectric refrigerator.
