Formation of uniform PbS quantum dots by a spin-assisted successive precipitation and anion exchange reaction process using PbX2 (X = Br, I) and Na2S precursors

We devised a straightforward spin-assisted successive precipitation and anion exchange reaction (spin-SPAER) process in order to deposit relatively uniform PbS quantum dots (QDs) on mesoporous TiO2 (mp-TiO2). For the spin-SPAER process, we used PbX2 (X = I, Br, and Cl) precursors instead of a Pb(NO3)2 precursor and consequently deposited individual PbS QDs on mp-TiO2 due to the suppressed overgrowth of PbS QDs, whereas the conventional spin-assisted successive ionic layer adsorption and reaction (spin-SILAR) process formed aggregated PbS QDs on the mp-TiO2 surface due to continuous adsorption and reaction. In addition, the PbS QDs prepared by spin-SPAER showed better air stability than the PbS QDs prepared by spin-SILAR possibly due to the passivation by halogen elements such as I and Br. Accordingly, we could improve the overall power conversion efficiency of PbS QD-SSCs prepared by the spin-SPAER process using PbI2 and PbBr2 precursors to ∼26.7% and ∼44.2%, respectively, compared to the PbS QD-SSCs prepared by spin-SILAR using the Pb(NO3)2 precursor.