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The relaxation of high-energy "hot" carriers in semiconductors is known to involve the redistribution of energy between hot and cold carriers, as well as the transfer of energy from hot carriers to phonons. Over the past few years, these two processes have been identified in lead-halide perovskites (LHPs) using ultrafast pump–probe experiments, but their interplay is not fully understood. Here we present a practical and intuitive kinetic model that accounts for the effects of both hot and cold carriers on carrier relaxation in LHPs. We apply this model to describe the dynamics of hot carriers in bulk and nanocrystalline CsPbBr3 as observed by multi-pulse "pump–push–probe" spectroscopy. The model captures the slowing of the relaxation dynamics in the materials as the number of hot carriers increases, which has previously been explained by a "hot-phonon bottleneck" mechanism. The model also correctly predicts an acceleration of the relaxation kinetics as the number of cold carriers in the samples is increased. Using a series of natural approximations, we reduce our model to a simple form containing terms for the carrier–carrier and carrier–phonon interactions. The model can be instrumental for evaluating the details of carrier relaxation and carrier–phonon couplings in LHPs and other soft optoelectronic materials. [ABSTRACT FROM AUTHOR]

We present a comparison of the potential distribution along the cross section of bilayer poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 (P3HT/PCBM) solar cells, which show normal and anomalous, S-shaped current-voltage (IV) characteristics. We expose the cross sections of the devices with a focussed ion beam and measure them with scanning Kelvin probe microscopy. We find that in the case of S-shaped IV-characteristics, there is a huge potential drop at the PCBM/Al top contact, which does not occur in solar cells with normal IV-characteristics. This behavior confirms the assumption that S-shaped curves are caused by hindered charge transport at interfaces. [ABSTRACT FROM AUTHOR]

Unicolored phosphor‐sensitized fluorescence (UPSF) is a dual emitting concept proposed for improving efficiencies and operational lifetimes of blue organic light emitting diodes (OLEDs). To overcome the limitations of the individual emitters, it uses a phosphorescent donor to sensitize a fluorescent acceptor. To quantify the potential of the concept, a multiscale model of a UPSF OLED is developed. It starts from atomistic morphologies, the rates of all processes on the available experimental data are parameterized, and the respective master equation is solved with the help of the kinetic Monte Carlo algorithm. The simulations show that the energy transfer between donor molecules is essential to reproduce the results of the time‐resolved photoluminescence experiment. The scope of the experiment is expanded by studying the effect of the acceptor concentration, as well as Förster and (parasitic) Dexter energy transfer from the donor to acceptor, on the characteristics of the UPSF OLED. The study shows that an appropriate material design can further improve efficiency by more than 30% and at the same time achieve radiative decay times below 0.02 µs, thus significantly extending OLED operational lifetime. [ABSTRACT FROM AUTHOR]

Improving lifetimes and efficiencies of blue organic light-emitting diodes is clearly a scientific challenge. Towards solving this challenge, we propose a unicolored phosphor-sensitized fluorescence approach, with phosphorescent and fluorescent emitters tailored to preserve the initial color of phosphorescence. Using this approach, we design an efficient sky-blue light-emitting diode with radiative decay times in the submicrosecond regime. By changing the concentration of fluorescent emitter, we show that the lifetime is proportional to the reduction of the radiative decay time and tune the operational stability to lifetimes of up to 320 h (80% decay, initial luminance of 1000 cd/m2). Unicolored phosphor-sensitized fluorescence provides a clear path towards efficient and stable blue light-emitting diodes, helping to overcome the limitations of thermally activated delayed fluorescence. The potential of organic light-emitting diodes (OLEDs) for solid-state lighting applications is limited by the need to develop efficient blue emitters. Here, the authors utilize a unicolored phosphor-sensitized fluorescence strategy to demonstrate efficient sky-blue OLEDs with enhanced lifetime. [ABSTRACT FROM AUTHOR]

The increase of exposure to volatile organic compounds in general, and endocrine disruptors in particular, through daily healthcare consumer goods urgently calls for the development and commercialization of cheap and easy‐to‐use sensors to detect these molecules in air. Organic semiconductors (OSCs) promise the mass fabrication of cheap and flexible sensors, under the condition that the fabrication of functional thin films having the right morphology can be fully harnessed. Nanoporous morphologies are interesting in the field of gas sensing because they facilitate the diffusion of gas molecules to the active volume of organic field‐effect transistors (OFETs), at the vicinity of the gate dielectric. Nanoporous films of OSCs are, however, challenging to produce and to transfer into working sensors. Usage of nanoporous OSC films deposited on a sensitive 4‐tert‐butylcalix[6]arene gate dielectric as the active layer of an OFET‐based gas sensor is proposed here. The semiconducting molecules are self‐assembled into nanoporous films at the interface between air and water, allowing their transfer to practically any gas‐sensitive dielectric substrate. The OFET built on this film stack is used here to sense the presence of methyl 4‐hydroxybenzoate (methylparaben) in air at concentrations below 1 ppb. A nanoporous layer of organic semiconductor deposited on a sensitive calixarene‐based gate dielectric allows sub‐ppb detection of methylparaben in air. The nanoporous layer is interfacially self‐assembled, allowing its facile transfer on the sensitive dielectric. Its morphology guarantees the access of the methylparaben analyte to the zone where the sensitive dielectric is in contact with the organic semiconductor. [ABSTRACT FROM AUTHOR]