The reported photocurrent density (J SC) of PbS quantum dot (QD)-sensitized solar cell was less than 19 mA/cm2 despite the capability to generate 38 mA/cm2, which results from inefficient electron injection and fast charge recombination. Here, we report on a PbS:Hg QD-sensitized solar cell with an unprecedentedly high J SC of 30 mA/cm2. By Hg 2+ doping into PbS, J SC is almost doubled with improved stability. Femtosecond transient study confirms that the improved J SC is due to enhanced electron injection and suppressed charge recombination. EXAFS reveals that Pb-S bond is reinforced and structural disorder is reduced by interstitially incorporated Hg2+, which is responsible for the enhanced electron injection, suppressed recombination and stability. Thanks to the extremely high J SC, power conversion efficiency of 5.6% is demonstrated at one sun illumination.