Efficient light detection in the near-infrared (NIR) wavelength region is central to emerging applications such as medical imaging and machine vision. An organic upconverter (OUC) consists of a NIR-sensitive organic photodetector (OPD) and an visible organic light-emitting diode (OLED), connected in series. The device converts NIR light directly to visible light, allowing imaging of a NIR scene in the visible. Here, we present an OUC composed of a NIR-selective squaraine dye-based OPD and a fluorescent OLED. The OPD has a peak sensitivity at 980 nm and an internal photon-to-current conversion efficiency of ∼100%. The OUC conversion efficiency (0.27%) of NIR to visible light is close to the expected maximum. The materials of the OUC multilayer stack absorb very little light in the visible wavelength range. In combination with an optimized semitransparent metal top electrode, this enabled the fabrication of transparent OUCs with an average visible transmittance of 65% and a peak transmittance of 80% at 620 nm. Visibly transparent OUCs are interesting for window-integrated electronic circuits or imaging systems that allow for the simultaneous detection of directly transmitted visible and NIR upconverted light.

No abstract

The improvement of photocatalytic activity of TiO2-based nanomaterials is widely investigated due to the tentative of their industrialization as environmental photocatalysts and their inherently low solar spectrum sensitivity and rapid recombination of charge carriers. Coupling of oxygen-based bidentate diketone to nanocrystalline TiO2 represents a potential alternative for improving the holdbacks. Formation of TiO2-acetylacetone charge transfer complex (CTC) by sol-gel route results in a hybrid semiconductor material with photodegradation activity against toxic NOx gas. In this research, the influence of the chelating agent acetylacetone (ACAC) content on the CTC photocatalytic efficiency under visible light was evaluated. A high content of ACAC in the CTC is not a decisive factor for efficiency of photocatalytic reactions. In fact, the highest efficiency for NOx degradation (close to 100%, during 1 h of visible light exposure) was reported for the material calcined in air at 300 °C with the content of strongly bonded acetylacetone not higher than 3 wt.%. Higher calcination temperature (400 °C) left TiO2 almost completely depleted in ACAC, while at the highest applied temperature (550 °C) a portion of anatase was transformed into rutile and the sample is free of ACAC. The analyses pointed out that superoxide anion radical (O2−) plays an active role in photo-oxidation of NOx. Our findings indicate that this CTC has both high visible light spectral sensitivity and photocatalytic efficiency.

No abstract

No abstract

The growing interest in near-infrared (NIR) imaging is explained by the increasing number of applications in this spectral range, which includes process monitoring and medical imaging. NIR-to-visible optical upconverters made by integrating a NIR photosensitive unit with a visible emitting unit convert incident NIR light to visible light, allowing imaging of a NIR scene directly with the naked eye. Optical upconverters made entirely from organic and hybrid materialswhich include colloidal quantum dots, and metal-halide perovskitesenable low-cost and pixel-free NIR imaging. These devices have emerged as a promising addition to current NIR imagers based on inorganic semiconductor photodiode arrays interconnected with read-out integrated circuitry. Here, we review the recent progress in the field of optical upconverters made from organic and hybrid materials, explain their functionality and characterization, and identify open challenges and opportunities.

In recent years the use of solvent additives for fabrication of polymer-based solar cells has become an important procedure to induce morphological changes at the system nanoscale, a critical step to improve device performance. Yet the actual effects of those additives on the polymer’s backbone conformations (with coupled variations on the electronic structure) remain very elusive. By combining different experimental and theoretical techniques, we show that the use of the solvent additive 1,8-diiodooctane (DIO) might influence the conformation of poly­[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) chains resulting in improved properties of the film. We correlate this conformational variation with the photovoltaic response of F8T2:fullerene­(C60) devices prepared using different DIO concentrations. We find that the efficiency of the devices increases more than 100%, and the hole mobility in the F8T2 films increases almost 1 order of magnitude with the use of DIO. A comparison between experimental data and the properties of the calculated structures suggests that the additive induces a higher density of syn conformers in the bithiophene unit of the copolymer backbone, planarizing the polymer’s geometry. The simulations indicate that this transition is very likely mediated by the electrostatic interaction between the iodine atom of the DIO and the heteroatoms of the bithiophene moiety. The higher degree of electronic delocalization and the enhancement of the interchain interactions improve the transport and the photovoltaic features of F8T2 layers. The use of solvent additive treatments to control conformational variations of the backbone might be a promising strategy to improve the optoelectronic properties of polymer-based devices.

No abstract