An insight into the surface engineering of colloidal PbSe quantum dots for polymer hybrid photovoltaic applications

In this article, the beneficial effect of surface passivation rendered by the amalgamation of co-ordinating tri-n-octylphophine (TOP), oleylamine (OLA), and oleic acid mixture on the structural and optoelectronic properties of lead selenide (PbSe) quantum dots (QDs) (~6–20 nm) and its respective poly(3-hexylthiophene) (P3HT) polymer: PbSe composites has been demonstrated. Here, OLA ligand is found to play a major role in the nucleation and growth mechanism and hence control of the size distribution of the resultant PbSe QDs. The superior quality of the OLA-passivated PbSe QDs can be attributed to its better homogeneity, colloidal and photostability, which it imparts to its respective polymer: PbSe composites as compared to the corresponding OA-passivated PbSe QDs. The role of post-synthesis ligand exchange/removal has been envisaged to facilitate efficient charge transport in hybrid composites and has been modeled pictorially. Accordingly, P3HT: PbSe (OLA) composites exhibit significant PL quenching and hence higher current and better charge transfer characteristics as compared to their OA-counterparts. An exhaustive structural, optical and electrical investigations as corroborated by various complimentary techniques (TEM/SEM, XRD, NMR, FTIR, NIR-Absorption, PL, XPS, and I-V) have resulted in some significant findings wherein the effective stabilizing and etching properties with an optimum binding capability of OLA ligands to PbSe surface are found to be imperative for its effective utilization in hybrid composite photovoltaic devices. The superior morphology, optical properties, and higher stability of OLA-capped PbSe QDs can aid in the proper understanding of efficient charge separation and transport in hybrid organic–inorganic nanocomposites solar cells based on colloidal PbSe nanocrystals.