The efficiency of tandem pn-dye-sensitized solar cells (pn-DSCs) has been limited by the poor performance of the available p-DSCs. A facile approach of introducing a compact NiO blocking layer into an active NiO photocathode network of p-DSCs and pn-DSCs is presented to enrich the power conversion efficiency (PCE) using a Co2+/3+ redox mediator. Two photoelectrodes sensitized with different dyes (SQ for n-DSC and P1 for p-DSC) have a complementary nature in absorbing solar irradiation at different wavelengths. The constructed pn-DSC demonstrates an enhanced photovoltage compared to n-DSC, resulting in an overall PCE of 1.486%. This PCE is further improved to 1.913% by the addition of an optimized NiO blocking layer to the p-DSC; this was prepared via spin-coating with a nickel acetate precursor solution. All photovoltaic parameters were significantly increased with the introduction of a blocking layer compared to a bare cell.