All-PbS colloidal quantum dot tandem solar cells with an ITO interlayer: A combined simulation and experimental study

Colloidal quantum dot (CQD) solar cells hold great promise for applications in single-junction and tandem solar cells owing to their adaptable bandgaps. However, power conversion efficiencies (PCEs) of their tandem solar cells still lag far behind their single-junction counterparts, primarily due to suboptimal thicknesses of light harvesting layers and underexplored interlayers for efficient charge recombination. In this study, Silvaco TCAD simulation is first conducted to optimize absorbing layer thickness in the front and rear sub-cells, enabling ideal photocurrent matching. Then, indium tin oxide (ITO) is introduced as an interlayer in a PbS CQD tandem solar cell to achieve efficient charge recombination. Guided by these simulation results, a two-terminal solution-processed PbS CQD tandem solar cell with an ITO interlayer is experimentally fabricated and characterized, which therefore achieved a PCE of 7.4% whereas the control device without an ITO interlayer only delivered a PCE of less than 1%. Therefore, this work offers insights into thickness optimizations of active layers and interlayer engineering for high-performance tandem solar cells, providing a theoretical and experimental guideline for optimizing CQD tandem devices.