Jaime Benavides

Functionalized multi-wall carbon nanotubes/TiO2 composites as efficient photoanodes for dye sensitized solar cells

We report on the effects of incorporation of different concentrations of carboxyl group (COOH)-functionalized multi-wall carbon nanotubes (F-MWCNTs) into TiO2 active layers for dye-sensitized solar cells (DSSCs). Standard DSSCs with bare TiO2 exhibit a photo-conversion efficiency (PCE) of 6.05% and a short circuit current density (Jsc) of 13.3 mA cm−2. The presence of 2 wt% F-MWCNTs in the photoanodes increases the PCE up to 7.95% and Jsc up to 17.5 mA cm−2. The photoanodes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The electrochemical behaviour of the solar cells was investigated by electrochemical impedance spectroscopy (EIS). We attribute the improved performances to the combined effect of increased dye loading and reduced charge recombination (as clarified by dye loading and EIS measurements), due to the conformal coverage of F-MWCNTs, which allows fast and efficient charge collection in operating solar cells. These results can help in improving the PCE in DSSCs in an elegant and straightforward way, minimizing the need of additional steps (e.g. pre- and post-treatment with TiCl4) for photoanode preparation.

Interconnected TiO2 Nanowire Networks for PbS Quantum Dot Solar Cell Applications

We present a simple method for the fabrication of an interconnected porous TiO2 nanostructured film via dip coating in a colloidal suspension of ultrathin TiO2 nanowires followed by high-temperature annealing. The spheroidization of the nanowires and the fusing of the loosely packed nanowire films at the contact points lead to the formation of nanopores. Using this interconnected TiO2 nanowire network for electron transport, a PbS/TiO2 heterojunction solar cell with a large short-circuit current of 2.5 mA/cm2, a Voc of 0.6 V, and a power conversion efficiency of 5.4% is achieved under 8.5 mW/cm2 white light illumination. Compared to conventional planar TiO2 film structures, these results suggest superior electron transport properties while still providing the large interfacial area between PbS quantum dots and TiO2 required for efficient exciton dissociation.

Tailored Interfaces of the Bulk Silicon Nanowire/TiO2 Heterojunction Promoting Enhanced Photovoltaic Performances

We report significantly improved silicon nanowire/TiO2 n+–n heterojunction solar cells prepared by sol–gel synthesis of TiO2 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.

Colloidal Ag Nanoparticles Enhanced Polymer-LEDs by Exciton-Surface Plasmon Coupling

We report high performance enhancement in an all-solution processed polymer LED by incorporating large density of colloidal Ag nanoparticles. A 11-fold maximum luminance enhancement and a 20-fold maximum current efficiency enhancement are observed.

Hybrid polymer-nanocrystal heterostructures for high-performance chip-integrated near-infrared LEDs

We report an all solution-based method producing hybrid heterostructures with efficient light-emission in the near-infrared. This robust, low-cost and versatile architecture is especially useful for flexible or reconfigurable optoelectronics, energy harvesting and biosensing chip-integrated platforms.

Synthesis of mesoporous TiO2 nanowire film for high performance PbS/TiO2 heterojunction photovoltaic devices

We report on the fabrication of mesoporous TiO2 nanowire film for PbS/TiO2 heterojuction solar cells. We achieved improved short circuit current and a remarkable power converting efficiency of 5.5% under 8.5 mW/cm2 white light illumination.

Hybrid Multilayered Heterostructures for High-Performance Near-Infrared LEDs

We report a solution-based method producing hybrid heterostructures for light-emission in the near-IR. This low-cost and versatile approach is most useful for flexible or reconfigurable optoelectronics, energy harvesting and biosensing platforms.