In　this　study,　we　investigate　the　effect　of　residual　H2O　pressure　(P-H2O)　on　the　structural,　electrical,　and　optical　properties　of　indium　tin　oxide　(ITO)　film　and　the　current-voltage　(I-V)　performance　of　silicon　heterojunction　(SHJ)　solar　cells.　The　ITO　films　and　SHJ　solar　cell　were　prepared　under　different　P-H2O　(3.75　x　10(-7)　Pa,　6　x　10(-7)　Pa,　10.25　x　10(-7)　Pa)　by　varying　the　pumping　time　before　starting　the　fabrication　process.　The　experimental　results　revealed　the　crystallinity　of　ITO　films　was　suppressed　with　the　increase　in　P-H2O.　Further,　the　sheet　resistance　of　ITO　films　was　reduced　from　103　O/sq　to　60　O/sq　due　to　the　enhanced　carrier　mobility,　and　the　transmittance　in　near-infrared　(NIR)　region　exhibited　a　slight　increase,　but　the　conversion　efficiency　of　SHJ　solar　cells　dropped　dramatically　from　23.3%　to　22.79%　due　to　the　degradation　of　fill　factor　(FF).　The　analysis　on　n-a-Si:H/ITO　and　ITO/Ag　contact　properties　indicated　that　such　FF　degradation　could　be　attributed　to　the　increased　specific　contact　resistance　for　the　two　contacts,　when　P-H2O　was　high.　Finally,　SHJ　solar　cell　with　conversion　efficiency　of　23.53%　was　achieved　by　restraining　the　residual　H2O　vapor　during　ITO　deposition　along　with　the　optimization　of　transmittance　in　NIR　region　by　adjusting　the　amount　of　O-2　flow.