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Ternary metal chalcogenide nanocrystals (NCs) offer exciting opportunities as novel materials to be explored on the nanoscale showing optoelectronic properties tunable with size and composition. CuInS (CIS) NCs are the most widely studied representatives of this family as they can be easily prepared with good size control and in high yield by reacting the metal precursors (copper iodide and indium acetate) in dodecanethiol (DDT). Despite the widespread use of this synthesis method, both the reaction mechanism and the surface state of the obtained NCs remain elusive. Here, we perform in situ X-ray diffraction using synchrotron radiation to monitor the pre- and postnucleation stages of the formation of CIS NCs. SAXS measurements show that the reaction intermediate formed at 100 °C presents a periodic lamellar structure with a characteristic spacing of 34.9 Å. WAXS measurements performed after nucleation of the CIS NCs at 230 °C demonstrate that their growth kinetics depend on the degree of precursor conversion achieved in the initial stage at 100 °C. NC formation requires the cleavage of S-C bonds. We reveal by means of combined 1D and 2D proton and carbon NMR analyses that the generated dodecyl radicals lead to the formation of a new thioether species R-S-R. The latter is part of a ligand double layer, which consists of dynamically bound dodecanethiolate ligands as well as of head-to-tail bound R-S-R molecules. This ligand double layer and a high ligand density (3.6 DDT molecules per nm) are at the origin of the apparent difficulty to functionalize the surface of CIS NCs obtained with the DDT method.

Diff erential pulse voltammetry and cyclic voltammetry reveal the modifi cation of the electronic energy levels of CdSe nanocrystals' thin fi lms upon surface ligand exchange with appropriate small molecules, leading to strongly enhanced conductivity.In recent years the treatment of thin films of nanocrystals (NCs) with short monofunctional or bifunctional bridging ligands has commonly been used to improve the conductivity within the NCs' assemblies. How does this surface ligand exchange in the solid state influence the electronic energy levels of the system? We show that electrochemical studies and in particular differential pulse voltammetry (DPV) can be used to give an answer to this question. Combined UV-vis, DPV and cyclic voltammetry data reveal that a shift of several tens of meV of the NCs' HOMO and LUMO levels takes place upon surface ligand exchange. As objects of our study we have selected thin solid films of stearic acid and oleylamine capped CdSe NCs, which were treated with acetonitrile solutions of 1,2ethanedithiol, butylamine, phenylenediamine, benzenedithiol and pyridine to induce the ligand exchange in the solid state, confirmed by FTIR spectroscopy. The resulting modified films exhibit strongly enhanced conductivity as compared to the films constituted of pristine NCs. Results and discussionThe solid state exchange with the following ligands was investigated: n-butylamine, p-phenylenediamine, pyridine, 1,2-ethanedithiol (EDT), p-benzenedithiol (BDT). To elucidate the effect of

Geminate recombination of bound polaron pairs at the donor/acceptor interface is one of the major loss mechanisms in organic bulk heterojunction solar cells. One way to overcome Coulomb attraction between opposite charge carriers and to achieve their full dissociation is the introduction of high dielectric permittivity materials such as nanoparticles of narrow band gap semiconductors. We selected CuInS2 nanocrystals of 7.4 nm size, which present intermediate energy levels with respect to poly(3-hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). Efficient charge transfer from P3HT to nanocrystals takes place as evidenced by light-induced electron spin resonance. Charge transfer between nanocrystals and PCBM only occurs after replacing bulky dodecanethiol (DDT) surface ligands with shorter 1,2-ethylhexanethiol (EHT) ligands. Solar cells containing in the active layer a ternary blend of P3HT:PCBM:CuInS2-EHT nanocrystals in 1:1:0.5 mass ratio show strongly improved short circuit current density and a higher fill factor with respect to the P3HT:PCBM reference device. Complementary measurements of the absorption properties, external quantum efficiency and charge carrier mobility indicate that enhanced charge separation in the ternary blend is at the origin of the observed behavior. The same trend is observed for blends using the glassy polymer poly(triarylamine) (PTAA).

tert-butylthiol (tBuSH) is used as the sulfur source, surface ligand and co-solvent in the synthesis of CuInS2 nanocrystals (NCs). The presented method gives direct access to short-ligand-capped NCs without post-synthetic ligand exchange. The obtained 5 nm CuInS2 NCs crystallize in the cubic sphalerite phase with space group F-43m and a lattice parameter a=5.65 Å. Their comparably large optical and electrochemical band gap of 2.6-2.7 eV is attributed to iodine incorporation into the crystal structure as reflected by the composition Cu1.04 In0.96 S1.84 I0.62 determined by EDX. Conductivity measurements on thin films of the tBuSH-capped NCs result in a value of 2.5(.) 10(-2)  S m(-1) , which represents an increase by a factor of 400 compared to established dodecanethiol-capped CuInS2 NCs.

Transfers of photoexcited electrons between poly(thieno[3,4-c]pyrrole-4,6-dione)-based copolymers (push–pull type) and fullerene or nanocrystals were studied by light-induced electron paramagnetic resonance (EPR). EPR tracing methodology has been used: EPR signatures of the various species taking part in the electron-transfer processes were determined and used to monitor potential charge transfers in the studied composites. The EPR tracing method combined with DFT calculations revealed that excited electrons are not only promoted from the HOMO of the polymer but also from its HOMO – 1 and even HOMO – 2, which are either exclusively centered on the push moiety or delocalized over both the push and pull units.

Among inorganic semiconductors, ternary and quaternary chalcogenides have attracted interest as light absorbers in photovoltaic applications. Cu 2 ZnSnS 4 (CZTS) has drown considerable attention as it has band‐gap suitable for solar‐harvesting applications, it shows p‐type conductivity and a high absorption coefficient. Moreover it only consists of inexpensive, non‐toxic and earth‐abundant materials. Synthesis by wet‐chemical methods are promising alternatives to physical deposition processes, as more easily implemented and cheaper. One of the challenges in the synthesis of colloidal CZTS nanocrystals is the control of internal structure and composition, which influence significantly their optoelectronic properties [1]. In this presentation we show the evidence of cation ordering in CZTS structure thanks to STEM HAADF imaging and we analyze nanocrystals homogeneity and composition by STEM EDX. CZTS nanocrystals were syntesized following an heating‐up method [2]. The first stage of the synthesis consists in a 30 minutes pre‐heating at 110°C of the organometallic precursors mixed in oleylamine. Then, CZTS nCs are obtained by increasing the mixing temperature up to 280°C and keeping it constant for one hour. The presence of long‐chained organic ligands passivating the surface of nanocrystals is fundamental for avoiding agglomeration in solution phase, it allows a slow and controlled growth; nevertheless it is detrimental for application in devices and for electron microscopy studies, in particular in spectroscopy (where contamination is critical). By drop‐casting the sample on graphene membranes, we could test the influence of several purification strategies. Thanks to the low‐contrast support we could image the unwanted parasitic residuals. In particular we proved the efficiency of solvent/antisolvent chloroform/aceton + acetic acid dispersion cycles [3]. HRTEM characterization was performed ex‐situ. HRTEM and STEM‐HAADF images were used to measure size dispersion of the nanocrystals. HRSTEM‐HAADF is sensible to chemical contrast, the signal being dependent on the atomic number Z; it is then possible to observe the sites occupied by the heavier atoms (Sn) in the structure, and distinguish then between kesterite (space group I‐4) or stannite (space group I‐42m) and pre‐mixed Cu‐Au (PMCA, space group P‐42m) structures, which show different characteristic “bright” motifs. The latter (PCMA) structure was the one found when nanocrystals were showing the good direction for phase identification (111). HRSTEM‐HAADF experimental images were compared with simulated ones obtained by multislice method and thermal diffusion scattering approximation [4]. STEM‐EDX was carried out on a dedicated FEI Themis with SuperX detector, in order to ensure chemical homogeneity between nanocrystals and inside a single crystal. Spectra were analyzed and quantified using Bruker Esprit 1.9 software.An overview of the nucleation and growing process was obtained by in‐situ Wide‐Angle X‐ray Scattering (WAXS) and Small‐Angle X‐ray Scattering (SAXS), performed on the ID01 beamline at the European Synchrotron Radiation Facility.

The Inside Cover picture shows short ligand‐capped CuInS2 nanocrystals (red), which are synthesized by using tert‐buthylthiol as the sulfur source, ligand, and co‐solvent. They show a 400‐fold increase in conductivity compared to nanocrystals capped with dodecanethiol (blue).More details can be found in the Communication by P. Reiss and co‐workers on page 654 in Issue 5, 2016 (DOI: 10.1002/cphc.201500800).