Cu-deficient CuInS2 quantum dots (QDs) synthesized by varying the [Cu]:[In] ratio allow modulation of optical properties as well as identification of the radiative emission pathways. Absorption and emission spectral features showed a strong dependence on the [Cu]:[In] ratio of CuxInS2 QDs, indicating two independent optical transitions. These effects are pronounced in transient absorption spectra. The bleaching of band edge absorption and broad tail absorption bands in the subpicosecond-nanosecond time scale provide further evidence for the dual optical transitions. The recombination process as monitored by photoemission decay indicated the involvement of surface traps in addition to the bandgap and sub-bandgap transitions. Better understanding of the origin of the optical transitions and their influence on the photodynamics will enable utilization of ternary semiconductor quantum dots in display and photovoltaic devices.

The optical and electronic properties of quantum dots (QDs), which are drastically affected by their size, have a major impact on their performance in devices such as solar cells. We now report the size-dependent solar cell performance for CuInS 2 QDs capped with 1dodecanethiol. Pyramidal shaped CuInS 2 QDs with diameters between 2.9 and 5.3 nm have been synthesized and assembled on mesoscopic TiO 2 films by electrophoretic deposition. Time-resolved emission and transient absorption spectroscopy measurements have ascertained the role of internal and surface defects in determining the solar cell performance. An increase in power conversion efficiency (PCE) was observed with the increasing size of QDs, with maximum values of 2.14 and 2.51% for 3.9 and 4.3 nm size particles, respectively. The drop in PCE observed for larger QDs (5.3 nm) is attributed to decreased charge separation following bandgap excitation. Because the origin of photocurrent generation in CuInS 2 QDSC arises from the defect-dominated charge carriers, it offers the opportunity to further improve the efficiency by controlling these defect concentrations.

Due to its ∼2.4 eV band gap, BiVO 4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO 3 /BiVO 4 heterojunction films, the electrons photoexcited in BiVO 4 are injected into WO 3 , overcoming the lower charge carriers' diffusion properties limiting the PEC performance of BiVO 4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO 4 excitation, a favorable electron transfer from photoexcited BiVO 4 to WO 3 occurs immediately after excitation and leads to an increase of the trapped holes' lifetime in BiVO 4 . However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO 4 . PEC measurements reveal the implication of these wavelengthdependent ultrafast interactions on the performances of the WO 3 /BiVO 4 heterojunction.

Multinary quantum dots such as AgInS and alloyed AgInS-ZnS are an emerging class of semiconductor materials for applications in photovoltaic and display devices. The nanocrystals of (AgInS)-(ZnS) (for x = 0.67) exhibit a broad emission with a maximum at 623 nm and interact strongly with TiO nanostructures by injecting electrons from the excited state. The electron transfer rate constant as determined from transient absorption spectroscopy was 1.8 × 10 s. The photovoltaic performance was evaluated over a period of a few weeks to demonstrate the stability of AgInS-ZnS when utilized as sensitizers in solar cells. We report a power conversion efficiency of 2.25% of our champion cell 1 month after its fabrication. The limitations of AgInS-ZnS nanocrystals in achieving greater solar cell efficiency are discussed.

Complexation of copper(I) with the binucleating ligand, 1,3-bis(9-methyl-1,10-phenanthrolin-2-yl)propane, mphenpr, result in formation of helical dimers, [Cu2(mphenpr)2](2+). The resolution of the enantiomeric forms of the dimers has been carried out with Δ-[As(cat)3](-) as resolving agent and X-ray structures for two compounds, P-[Cu2(mphenpr)2](Δ-[As(cat)3])2 and P-[Cu2(mphenpr)2](Δ-[As(cat)3])2·4(CH3CN), are reported. The rate of racemization in poorly-coordinating solvents has been examined by (1)H NMR, and is slow. At saturating concentrations of [[Cu2(mphenpr)2](2+)] in acetonitrile, crystals of the helical trimeric complex [Cu3(mphenpr)3](ClO4)3 are obtained. The X-ray structure of the trimer is reported. This species has also been resolved. As with the helical dimer, racemization in poorly-coordinating solvents is slow, and circular dichroism and (1)H NMR spectra are reported. The absolute configuration of the resolved complex, P-[Cu3(mphenpr)3](Δ-[As(cat)3])3, has been determined by X-ray crystallography.