Ultrasmall PbS quantum dots: a facile and greener synthetic route and their high performance in luminescent solar concentrators

Abstract

Synthesis of quantum dots (QDs) with widely size-tunable optical absorption and high photoluminescence quantum yield (PL QY) via a facile route is highly desired. By introducing tributylphosphine (TBP) into a relatively green synthesis method based on the use of S, PbCl₂ and oleylamine (OLA), we conveniently synthesized ultrasmall PbS QDs with the first excitonic absorption peak wavelength as short as 705 nm, without using a glove box, which cannot be achieved by previously reported approaches, without involving smelly S precursors (such as bis(trimethylsilyl) sulfide). Such synthesized PbS QDs show narrow size distributions without any aggregation and demonstrate high PL QY in the range of 60–90%, depending on the QD size. Based on nuclear magnetic resonance spectroscopy and X-ray diffraction investigations, TBP was found to act as the passivation ligand on the surface of QDs while simultaneously assisting the transformation of PbCl₂–OLA into more reactive Pb(OH)Cl that can directly participate the nucleation process, yielding ultrasmall PbS QDs. This new finding renders Pb(OH)Cl a very promising, new lead precursor for convenient synthesis of PbS and other lead-based QDs. We also demonstrate that the process can be readily scaled up. After synthesizing a thin CdS shell (∼0.1 nm), ultrasmall core/shell QDs with a large Stokes shift (0.36 eV) and good stability were employed for fabricating near infrared (NIR) luminescent solar concentrators, which led to a record-high optical efficiency of ∼1.2% at a geometric factor of ∼50 (10 cm in length). The TBP route developed herein is very promising for synthesizing high quality ultrasmall QDs that have high potential in NIR-related applications.