We report on the optoelectronic properties of ITO layers deposited by DC sputtering, using different oxygen to total flow ratios [r(O-2) = O-2/Ar, ranging from 1% to 8%], for silicon heterojunction (SHJ) solar cell application. The depth profiling of the various elements throughout the thicknesses and interfaces of the ITOs and thin films forming the SHJ device was determined by time-of-flight secondary ion mass spectrometry. Finally, the photovoltaic performance of the fabricated SHJ cells was evaluated with respect to the r(O-2) into the ITO layers. Lower r(O-2) was found to yield the best PV performance which is attributed to lower parasitic resistive losses.