In hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction (HJ) solar cell, the high contact resistance or high Schottky barrier at the back-surface field (BSF)/Indium Tin Oxide (ITO) is prejudicial to the majority carrier collections process, as it degrades the fill factor (FF), which in turn, cell efficiency. To minimize the contact resistance or Schottky barrier, high conductivity of the BSF layer is thus required. In this study, to preserve high BSF conductivity, while without prompting silicon dehydrate-related structural defects within the films, the high conductivity n-type hydrogenated microcrystalline Si layer (mc-Si:H(n+)), instead of standard n-type hydrogenated amorphous silicon, was employed as a BSF layer. The film conductivity (sd) of the mc-Si:H(n+) layer was improved from 0.16 (S/cm) to 4.16 (S/cm), as the crystalline fraction (Xc) increased from 6% to 89%. It was found that the FF tends depend on the contact resistance at the mc-Si:H(n+)/ITO interface, in defiance of Schottky contact behavior. Thus, series contact resistance dominates the FF of the device; this finding is opposite to previous report. Using a moderated crystalline fraction of 60% mc-Si:H(n+)-BSF, the photovoltaic parameter of the a-Si:H/c-Si HJ solar cells yielded an open-circuit voltage of up to 700 mV, in turn giving an efficiency >20%.