Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials.

We report on the fabrication of efficient PbS solar cells, showing power conversion efficiencies approaching 4% and fill factors of 60% under AM1.5 illumination. The effect of the size of two different nanocrystals (NCs) on the performance and key parameters of the devices are discussed together with peculiar features of device functioning. The results prove that the devices are not under space-charge limitation and the device performance is influenced by charge trapping which is dependent on the size of the NCs.

Nanocrystal/fullerene derivative inorganic-organic hybrid photodetectors exhibiting high detectivity for near-IR wavelengths and a linear power dependence are produced. The ultrafast electron transfer from the PbS crystals to the fullerene opens a new route to obtaining efficient photodetectors that are appealing, cost-effective alternatives to the currently available technology

Temperature‐dependent studies of the electrical and optical properties of cross‐linked PbS nanocrystal (NC) solar cells can provide deeper insight into their working mechanisms. It is demonstrated that the overall effect of temperature on the device efficiency originates from the temperature dependence of the open‐circuit voltage and the short‐circuit current, while the fill factor remains approximately constant. Extensive modeling provides signs of band‐like transport in the inhomogeneously coupled NC active layer and shows that the charge transport is dominated by diffusion. Moreover, via low temperature absorption and photoluminescence (PL) measurements, it is shown that the optical properties of PbS thin films before and after benzenedithiol (BDT) treatment exhibit very distinct behavior. After BDT treatment, both the optical density (OD) and PL are shifted to lower energies, indicating the occurrence of electronic wave function overlap between adjacent NCs. Decrease of the temperature leads to additional red‐shift of the OD and PL spectra, which is explained by the well‐known temperature dependence of the PbS NCs' bandgap. Moreover, BDT treated PbS NCs show unusual properties, such as decrease of the PL signal and broadening of the spectra at low temperatures. These features can be attributed to the partial relaxation of the quantum confinement and the opening of new radiative and nonradiative pathways for recombination at lower temperatures due to the presence of trap states.

We demonstrate solution processable all-polymer based field-effect transistors (FETs) exhibiting comparable electron and hole mobilities. The semiconducting layer is a bulk heterojunction of poly{[N,N 0-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 0-(2,2 0bithiophene)} (n-type polymer) and regioregular poly(3-hexylthiophene) (p-type polymer). These polymers form a type-II heterojunction as revealed by the faster photoluminescence dynamics of the blend compared to the pristine materials. An electron mobiliy of 4 Â 10 À3 cm 2 /V s and a hole mobility of 2 Â 10 À3 cm 2 /V s were extracted from the transfer characteristics of bottom contact FETs. The balanced mobilities suggest that the active layer is a fine network of the two components, as confirmed by atomic force microscopy phase images.

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We investigate a promising organic/inorganic hybrid composite for solution-processable optoelectronics made by lead sulphide nanoparticles and fullerene derivatives, which combine the sensitivity of PbS to the infrared spectrum with the good electron transport properties of fullerenes. Charge separation is the crucial process that determines whether the heterojunction can be the building block for devices converting photogenerated excitons into free charges flowing in a circuit. Subpicosecond spectroscopy techniques on bulk heterojunctions between PbS nanocrystals of various sizes and [6,6]-phenyl-61-butyric acid methyl ester (PCBM) were employed to reveal the ultrafast dynamics of photoexcited carriers, particularly transfer of photoexcited electrons from nanocrystals to PCBM. Electron transfer is found to critically depend on nanoparticle size, occurring for nanocrystals with diameter 4.4 nm and smaller, not for larger ones. Our findings are relevant to the engineering of hybrid solar cells and light detectors based on PbS nanocrystal/fullerene bulk heterojunctions

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