  Replacing the bulky cryo-liquid based cooling stages of cryo-enabled
instruments by chip scale refrigeration is envisioned to disruptively reduce
the system size similarly as microprocessors did for computers. Electronic
refrigerators based on superconducting tunnel junctions have been envisioned to
provide a solution, but reaching the necessary above 1 kelvin operation
temperature range has remained a goal out of reach for several decades. We show
efficient electronic refrigeration by Al-AlOx-Nb superconducting tunnel
junctions starting from bath temperatures above 2 K. The junctions can deliver
electronic cooling power up to $\sim$mW/mm$^2$, which enables us to demonstrate
tunnel current driven electron temperature reduction from 2.4 K to below 1.6 K
(34% relative cooling) against the phonon bath. Our work shows that the key
material of integrated superconducting circuits - niobium - enables powerful
cryogenic refrigerator technology. This result is a prerequisite for practical
cryogenic chip scale refrigerators and, at the same time, it introduces a new
electro-thermal tool for quantum heat transport experiments.
