Despite the promise of quantum dots (QDs) as a light-absorbing material to replace the dye in dye-sensitized solar cells, quantum dot-sensitized solar cell (QDSSC) efficiencies remain low, due in part to high rates of recombination. In this article, we demonstrate that ultrathin recombination barrier layers of Al 2 O 3 deposited by atomic layer deposition can improve the performance of cadmium sulfide (CdS) quantum dot-sensitized solar cells with spiro-OMeTAD as the solid-state hole transport material. We explored depositing the Al 2 O 3 barrier layers either before or after the QDs, resulting in TiO 2 /Al 2 O 3 /QD and TiO 2 /QD/Al 2 O 3 configurations. The effects of barrier layer configuration and thickness were tracked through current−voltage measurements of device performance and transient photovoltage measurements of electron lifetimes. The Al 2 O 3 layers were found to suppress dark current and increase electron lifetimes with increasing Al 2 O 3 thickness in both configurations. For thin barrier layers, gains in open-circuit voltage and concomitant increases in efficiency were observed, although at greater thicknesses, losses in photocurrent caused net decreases in efficiency. A close comparison of the electron lifetimes in TiO 2 in the TiO 2 /Al 2 O 3 /QD and TiO 2 /QD/Al 2 O 3 configurations suggests that electron transfer from TiO 2 to spiro-OMeTAD is a major source of recombination in ss-QDSSCs, though recombination of TiO 2 electrons with oxidized QDs can also limit electron lifetimes, particularly if the regeneration of oxidized QDs is hindered by a too-thick coating of the barrier layer.

Low degrees of symmetry breaking in initial states lead to full-blown symmetry breaking and improved predictions in time-dependent direct dynamics.

By replacing the dye in the dye-sensitized solar cell design with semiconductor quantum dots as the lightabsorbing material, solid-state quantum dot-sensitized solar cells (ss-QDSSCs) were fabricated. Cadmium sulfide quantum dots (QDs) were grown in situ by successive ion layer adsorption and reaction (SILAR). Aluminum oxide recombination barrier layers were deposited by atomic layer deposition (ALD) at the TiO 2 /hole-conductor interface. For low numbers of ALD cycles, the Al 2 O 3 barrier layer increased open circuit voltage, causing an increase in device efficiency. For thicker Al 2 O 3 barrier layers, photocurrent decreased substantially, leading to a decrease in device efficiency.Index Terms -quantum dots, surface engineering, charge carrier lifetime, photovoltaic cells. 978-

We propose an all‐optical switch based on cross‐polarization modulation in a semiconductor optical amplifier (SOA), operating at 2.5 Gbits/s with an NRZ pseudorandom data sequence. The effect consists of an induced modification of the birefringence and waveguide eigenmodes of an SOA produced by a strong control beam. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 205–208, 2001.

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