No abstract

AgInS2-ZnS (ZAIS) nanocrystals are very good candidates for easily synthesized, highly efficient cadmium-free nano-phosphors. They can be employed for the development of next generation white-LED technologies, taking advantage of their nanometric size. This paper describes the combined use of time-resolved emission spectroscopy and photoluminescence quantum yield measurements to quantitatively compare the efficiency of each recombination pathway involved in the photoluminescence of ZAIS nanocrystals. This approach, applied to nanocrystals of different sizes, compositions and surface chemistry revealed the critical role of surface effects. Moreover, we developed a new type of surface passivation that increases the photoluminescence quantum yield of all nanocrystal compositions by 15 to 20%. This molecular surface passivation can be applied as a replacement or in addition to the already established ZnS shell passivation method.

n -channel organic thin film transistors were fabricated on polyethylene naphthalate substrates. The first part of the paper is devoted to a critical analysis of eight methods to extract the threshold voltage from the transfer characteristic in the linear regime. Next, to improve electron injection and reduce contact resistance, self-assembled monolayers (SAMs) were deposited on the gold source and drain electrodes. The subsequent modification on the current-voltage characteristics of the transistors is analyzed by the transfer line method, using a threshold-voltage-corrected gate voltage. The improved performance of the device obtained with some of the SAM treatments is attributed to both a better morphology of the semiconductor film, resulting in an increased channel mobility, and to easier electron injection, which manifests itself through a lowering of the contact resistance. Interestingly, the modulation of the contact resistance exactly follows an opposite behavior to what reported in the case of p-channel devices, which brings further evidence for that charge injection is tuned by the direction and magnitude of the dipole moment of the SAM.