3 research outputs found
Plasmonic Nanocrystal Solar Cells Utilizing Strongly Confined Radiation
The ability of metal nanoparticles to concentrate light <i>via</i> the plasmon resonance represents a unique opportunity for funneling the solar energy in photovoltaic devices. The absorption enhancement in plasmonic solar cells is predicted to be particularly prominent when the size of metal features falls below 20 nm, causing the strong confinement of radiation modes. Unfortunately, the ultrashort lifetime of such near-field radiation makes harvesting the plasmon energy in small-diameter nanoparticles a challenging task. Here, we develop plasmonic solar cells that harness the near-field emission of 5 nm Au nanoparticles by transferring the plasmon energy to band gap transitions of PbS semiconductor nanocrystals. The interfaces of Au and PbS domains were designed to support a rapid energy transfer at rates that outpace the thermal dephasing of plasmon modes. We demonstrate that central to the device operation is the inorganic passivation of Au nanoparticles with a wide gap semiconductor, which reduces carrier scattering and simultaneously improves the stability of heat-prone plasmonic films. The contribution of the Au near-field emission toward the charge carrier generation was manifested through the observation of an enhanced short circuit current and improved power conversion efficiency of mixed (Au, PbS) solar cells, as measured relative to PbS-only devices
Suppressed Carrier Scattering in CdS-Encapsulated PbS Nanocrystal Films
One of the key challenges facing the realization of functional nanocrystal devices concerns the development of techniques for depositing colloidal nanocrystals into electrically coupled nanoparticle solids. This work compares several alternative strategies for the assembly of such films using an all-optical approach to the characterization of electron transport phenomena. By measuring excited carrier lifetimes in either ligand-linked or matrix-encapsulated PbS nanocrystal films containing a tunable fraction of insulating ZnS domains, we uniquely distinguish the dynamics of charge scattering on defects from other processes of exciton dissociation. The measured times are subsequently used to estimate the diffusion length and the carrier mobility for each film type within the hopping transport regime. It is demonstrated that nanocrystal films encapsulated into semiconductor matrices exhibit a lower probability of charge scattering than that of nanocrystal solids cross-linked with either 3-mercaptopropionic acid or 1,2-ethanedithiol molecular linkers. The suppression of carrier scattering in matrix-encapsulated nanocrystal films is attributed to a relatively low density of surface defects at nanocrystal/matrix interfaces
Infrared Emitting PbS Nanocrystal Solids through Matrix Encapsulation
Colloidal
semiconductor nanocrystals (NCs) are emerging as promising
infrared-emitting materials, which exhibit spectrally tunable fluorescence,
and offer the ease of thin-film solution processing. Presently, an
important challenge facing the development of nanocrystal infrared
emitters concerns the fact that both the emission quantum yield and
the stability of colloidal nanoparticles become compromised when nanoparticle
solutions are processed into solids. Here, we address this issue by
developing an assembly technique that encapsulates infrared-emitting
PbS NCs into crystalline CdS matrices, designed to preserve NC emission
characteristics upon film processing. An important feature of the
reported approach is the heteroepitaxial passivation of nanocrystal
surfaces with a CdS semiconductor, which shields nanoparticles from
the external environment leading to a superior thermal and chemical
stability. Here, the morphology of these matrices was designed to
suppress the nonradiative carrier decay, whereby increasing the exciton
lifetime up to 1 μs, and boosting the emission quantum yield
to an unprecedented 3.7% for inorganically encapsulated PbS NC solids