Interface Modification enables 11.95%‐Efficient All‐PbS‐QDs Tandem Solar Cells Utilizing Self‐Assembled Monolayers

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.