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

Azimi, Hamed, Kuhri, Susanne, Osvet, Andres, Matt, Gebhard, Khanzada, Laraib S., Lemmer, Mario, Luechinger, Norman A., Larsson, Mats I., Zeira, Eitan, Guldi, Dirk M., Brabec, Christoph J.
Journal of the American Chemical Society 2014 v.136 no.20 pp. 7233-7236
Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, absorption, cupric oxide, cuprous oxide, ligands, nanocrystals, nanoparticles, oxygen, pyrolysis, transmission electron microscopy
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.