The reported photocurrent density (J(SC)) of PbS quantum dot (QD)-sensitized solar cell was less than 19 mA/cm(2) despite the capability to generate 38 mA/cm(2), 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/cm(2). 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 Hg(2+), 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.