Benzenedithiol (BDT) and ethanedithiol (EDT) ligand-exchange treatments can be used to cross-link colloidal PbS quantum dots into nanocrystalline film structures with distinct optoelectronic properties. Such structures can provide a unique platform to study the energy transfer between layers of quantum dots with different sizes. In this report, efficient exciton funneling and recycling of surface state-bound excitons is observed in cascaded PbS quantum dot-based multilayered superstructures, where the excitons transfer from the larger band gap or donor layers to the smallest band gap or acceptor layers. In this system, both the BDT- and EDT-treated cascaded structures exhibit dramatically enhanced photoluminescence from the acceptor layers. As we show, the energy transfer mechanisms involved and their efficiencies are significantly different depending on the ligand-exchange treatment. In the future, we believe these efficient exciton recycling and funneling mechanisms could be used to improve significantly the photocurrent, charge-transport, and conversion efficiencies in low-cost nanocrystalline and hybrid solar cells and the emission efficiencies in hybrid light-emitting devices.
The incorporation of functionalized multi-wall carbon nanotubes into TiO2 mesoporous photoanodes for dye-sensitized solar cells leads to 30% enhancement in photoconversion efficiency of the optimized system.
Titanium dioxide (TiO 2 ) is a remarkable metal-oxide semiconductor with unique optoelectronic properties ideal for photovoltaics and photocatalytic conversion. The principal crystalline phases for TiO 2 are anatase, rutile, and brookite. The combination of both anatase and rutile crystalline structures can positively impact the optoelectronic properties of TiO 2 films. With standard sol−gel processing, hightemperature conversion generally yields one dominant phase and limits the combined use of anatase and rutile TiO 2 for optoelectronic devices. We report on a singular route to controllably engineer hybrid nanocrystalline films of TiO 2 at room temperature to synergistically exploit both anatase and rutile TiO 2 phases. Relying on sol−gel chemistry, this approach starts from an amorphous film and uses photoinduced activation using a low-power laser to achieve specific spatially controlled pattern consisting of different TiO 2 crystalline phases within the same film. While achieving remarkable precision, reproducibility, and control, we also avoid costly high-temperature, ion-metalassisted, or specific atmospheric processing that currently prevents the integration of TiO 2 in several optoelectronic platforms. In the future, we believe this unprecedented level of control and the ability to engineer the TiO 2 crystalline structure at the microscopic scale will allow the design and fabrication of novel high-performance TiO 2 hybrids for energy conversion and environmental applications.
We report significantly improved
silicon nanowire/TiO
2
n
+
–n heterojunction
solar cells prepared by sol–gel
synthesis of TiO
2
thin film atop vertically aligned silicon
nanowire arrays obtained by facile metal-assisted wet electroless
chemical etching of a bulk highly doped n-type silicon wafer. As we
show here, chemical treatment of the nanowire arrays prior to depositing
the sol–gel precursor has dramatic consequences on the device
performance. While hydrofluoric treatment to remove the native oxide
already improves significantly the device performances, hydrobromic
(HBr) treatment consistently yields by far the best device performances
with power conversion efficiencies ranging between 4.2 and 6.2% with
fill factors up to 60% under AM 1.5G illumination. In addition to
yield high-quality and easy to produce solar cell devices, these findings
regarding the surface treatment of silicon nanowires with HBr suggest
that HBr could contribute to the enhancement of the device performance
not only for solar cells but also for other optoelectronics devices
based on semiconductor nanostructures.
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