With increased interest in semiconductor nanoparticles for use in quantum dot solar cells there comes a need to understand the long-term photostability of such materials. Colloidal CdSe quantum dots (QDs) were suspended in toluene and stored in combinations of light/dark and N2/O2 to simulate four possible benchtop storage environments. CdSe QDs stored in a dark, oxygen-free environment were observed to better retain their optical properties over the course of 90 days. The excited state lifetimes, determined through femtosecond transient absorption spectroscopy, of air-equilibrated samples exposed to light exhibit a decrease in average lifetime (0.81 ns) when compared to samples stored in a nitrogen/dark environment (8.3 ns). A photoetching technique commonly used for controlled reduction of QD size was found to induce energetic trap states to CdSe QDs and accelerate the rate of electron–hole recombination. X-ray absorption near edge structure (XANES) analysis confirms surface oxidation, the extent of which is shown to be dependent on the thickness of the ligand shell.

Successive ionic layer adsorption and reaction (SILAR) is a popular method of depositing the metal chalcogenide semiconductor layer on the mesoscopic metal oxide films for designing quantum-dot-sensitized solar cells (QDSSCs) or extremely thin absorber (ETA) solar cells. While this deposition method exhibits higher loading of the light-absorbing semiconductor layer than direct adsorption of presynthesized colloidal quantum dots, the chemical identity of these nanostructures and the evolution of interfacial structure are poorly understood. We have now analyzed step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films using X-ray absorption near-edge structure analysis and probed the interfacial structure of these films. The film characteristics interestingly show dependence on the order in which the Cd and Se are deposited, and the CdSe-TiO2 interface is affected only during the first few cycles of deposition. Development of a SeO2 passivation layer in the SILAR-prepared films to form a TiO2/SeO2/CdSe junction facilitates an increase in photocurrents and power conversion efficiencies of quantum dot solar cells when these films are integrated as photoanodes in a photoelectrochemical solar cell.

Chemical bath deposition (CBD) offers a simple and inexpensive route to deposit semiconductor nanostructures, but lack of fundamental understanding and control of the underlying chemistry has limited its versatility. Here we report the first use of in situ X-ray absorption spectroscopy during CBD, enabling detailed investigation of both reaction mechanisms and kinetics of ZnO nanowire growth from zinc nitrate and hexamethylenetetramine (HMTA) precursors. Time-resolved X-ray absorption near-edge structure (XANES) spectra were used to quantify Zn(II) speciation in both solution and solid phases. ZnO crystallizes directly from [Zn(H2O)6]2+ without long-lived intermediates. Using ZnO nanowire deposition as an example, this study establishes in situ XANES spectroscopy as an excellent quantitative tool to understand CBD of nanomaterials.

Cd1–x Zn x S (CdZnS) is a promising replacement for the CdS buffer layers in copper indium gallium (di)selenide (CIGS) solar cells because the wider band gap of CdZnS offers improved optical transmittance of blue light. Chemical bath deposition (CBD) is the state-of-the-art deposition method for CdS and CdZnS. However, CBD of CdZnS is poorly understood, and relationships between bath composition and stoichiometry, microstructure, and optoelectronic properties of the deposited film are lacking. We introduce CBD using a continuous flow microreactor as a new technique to rapidly explore a wide variety of deposition conditions on a single substrate using spatially dependent characterization. X-ray diffraction and X-ray absorption spectroscopy indicate that the film is a mixture of nanocrystalline CdZnS and amorphous Zn(O,OH,S). Over the length of a single substrate, films showed increasing Zn:Cd ratio in the nanocrystalline phase, increasing amorphous content, and increasing quantum confinement, and resultant monotonic increase in band gap from 2.42 to 2.75 eV. Microreactor CBD (μR-CBD) enables rapid identification of CdZnS compositions that are ideal candidates for thin film photovoltaics, as well as determination of the CBD conditions required to deposit them.

We assessed the effects of posted feedback and warning ticket programs on speeding and accidents in two cities. In Experiment 1, speeding feedback signs were effective even when 10 were used in Dartmouth, Nova Scotia, and reductions in speeding were associated with reductions in accidents. The effectiveness of the signs was correlated with the number of intersections and residences within 0.5 km beyond them, and the signs had no effect on untreated streets. In Experiment 2, posted feedback and a warning program reduced speeding and accidents on 14 streets in Haifa, Israel.