The influence of ligands passivation on strength of Fermi level pinning in the quantum dots interface

[Display omitted] •The impact of Fermi level pinning on energy level alignment in PbS quantum dot is examined.•UPS analyses indicate that energetic position of PbS QD’s gap-state to be c.a. 4.0 eV.•The pinning factors (S) for PbS QD-EDT and PbS-TBAI are empirically determined by UPS and LEIPES.•Higher S for PbS-EDT indicate the TBAI more effectively passivates the gap-state of PbS QD. PbS quantum dots capped by ethanedithiol (PbS QD-EDT) and tetrabutylammonium iodide (PbS QD-TBAI) and supported by different substrates were examined in terms of Fermi level pinning (FLP), gap states, and electron and hole barriers (Φe and Φh, respectively) using ultraviolet and low-energy inverse photoemission spectroscopy. The former analysis showed that TBAI and EDT differed in their ability to induce gap-state passivation, with the corresponding energy difference determined as 4.0 eV. Two FLP regimes were identified: at substrate work function (Фsub) 4.0 eV, the pinning strength of PbS QD-EDT (S of Фb,h and Фb,e = 0.19 and 0.24, respectively) exceeded that of PbS QD-TBAI (S of Фb,h and Фb,e = 0.53 and 0.57, respectively). Thus, the gap states were more effectively passivated in the case of PbS QD-TBAI. Our results indicate the importance of considering FLP strength when working with high-work-function substrates for the design of optimized QD-based devices.