Significant improvements in silicon solar cell performance are reported using an improved high‐efficiency silicon solar cell structure. This structure overcomes deficiencies in an earlier structure by locally diffusing boron into contact areas at the rear of the cells. Terrestrial energy conversion efficiencies up to 24% are reported for silicon cells for the first time. Air Mass 0 efficiencies lie in the 20–21% range, the first silicon cells to exceed 20% efficiency under space illumination.