Photoactive p-type PbS as a counter electrode for quantum dot-sensitized solar cells

A photoactive PbS film synthesized by successive cycles of coating with ionic solutions and reaction can function as a performance-promoting counter electrode for quantum dot-sensitized solar cells (QDSSCs). The PbS film has a wide absorption spectrum that extends to the near infra-red region, making it capable of absorbing the long-wavelength light that penetrates the photoanode of a QDSSC. Under simulated one-sun illumination, this PbS film exhibits a p-type photovoltaic response in a polysulfide electrolyte, showing a quasi-Fermi level shift of +0.25 V. For QDSSCs consisting of a TiO2/CuInS2/CdS/ZnS photoanode and a polysulfide electrolyte, the PbS film outperforms Pt and CuS films as a counter electrode even though CuS has a much higher electrocatalytic activity in the polysulfide electrolyte than PbS. The photoactive characteristics of the PbS electrode increase the photocurrent of the resulting QDSSC. The p-type conductivity of the PbS forms a partial tandem junction between the PbS and the anode, increasing the photovoltage and the fill factor. Under one-sun illumination, a QDSSC assembled with the photoactive p-type PbS counter electrode achieves a maximum power conversion efficiency of 4.7%, which is more than 15% greater than that of a cell assembled with the highly electrocatalytically active CuS.