Silicon wafer processing system, apparatus and method of doping silicon wafers with hot concentrated acid dopant compositions for forming p-n junction and back contact layers during processing into PV solar cells. Highly concentrated acid dopant is atomized with pressurized gas and heated in the range of 80-200° C., then introduced into a concentrated acid vapor processing chamber to apply vapor over 1.5-6 min to wafers moving horizontally on a multi-lane conveyor system through the processing chamber. The wafers are dried and forwarded to a diffusion furnace. An optional UV pre-treatment assembly pre-conditions the wafers with UV radiation prior to dopant application, and doped wafers may be post-treated in a UV treatment module before being fired. The wafers may be cooled in the processing chamber. Post-firing, the wafers exhibit excellent sheet resistance in the 60-95Ω/sq range, and are highly uniform across the wafers and wafer-to-wafer.