Effective Ligand Passivation of Cu₂O Nanoparticles through Solid-State Treatment with Mercaptopropionic Acid

In colloidal nanoparticle (NPs) devices, trap state densities at their surface exert a profound impact on the rate of charge carrier recombination and, consequently, on the deterioration of the device performance. Here, we report on the successful application of a ligand exchange strategy to effectively passivate the surface of cuprite (Cu₂O) NPs. Cu₂O NPs were prepared by means of a novel synthetic route based on flame spray pyrolysis. FTIR, XRD, XPS, and HRTEM measurements corroborate the formation of cubic cuprite Cu₂O nanocrystals, excluding the possible presence of undesired CuO or Cu phases. Most importantly, steady-state emission and transient absorption assays document that surface passivation results in substantial changes in the intensity of emissive excitonic statescentered at copper and oxygen vacanciesand in the lifetime of excitons near the band edge. To shed light onto ultrafast processes in Cu₂O nanocrystals additional pump probe experiments on the femtosecond and nanosecond time scales were carried out. Two discernible species were observed: on one hand, an ultrafast component (∼ps) that relates to the excitons; on the other hand, a long-lived component (∼μs) that originates from the defects/trap states