The modification of the PbS-EDT/Au interface by self-assembled monolayers (SAMs) reduces the nonradiative recombination losses and facilitates the uniform distribution of thin Au recombination layer. As a result, the SAMs-based all-PbS quantum dots tandem solar cells achieve a record certified power conversion efficiency of 11.95%.
The bandgap tunability of lead sulfide (PbS) quantum dots (QDs) positions them as a promising candidate for tandem solar cells (TSCs). However, the power conversion efficiency (PCE) of all-PbS QDs TSCs is lagging much behind the theoretical efficiency limit due to the deficient carrier recombination capability of the interconnection layer (ICL). In this study, we fabricated all-PbS QDs TSCs utilizing 1.40 and 0.95 eV PbS QDs for the top and bottom subcells, respectively. We developed two kinds of ICLs, 1,2-ethanedithiol capped PbS QDs (PbS-EDT)/Au/ZnO and PbS-EDT/SAMs/Au/ZnO, where self-assembled monolayers (SAMs) of 4-(7H-dibenzo[c,g]carbazol-7-yl)butylphosphonic acid (4PADCB) were the first time applied for all-PbS QD TSCs. The SAMs bound with the PbS-EDT hole transport layer (HTL), enhancing hole extraction from the top cell via their conjugated π-system. Furthermore, they served to passivate traps at the HTL/Au interface, thereby reducing nonradiative recombination losses. Consequently, the top cell achieved 8.36% PCE with a semitransparent absorber layer. After the SAMs modification, it established a uniform and low-potential surface, facilitating a uniform distribution of a thin Au recombination layer (RL). The newly developed RL enhanced hole–electron recombination. The resulting SAMs-based TSCs achieved a certified PCE of 11.95%, more than 2% net PCE improvement over our last record data.
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