The exciton physics of organic semiconductors is exotic. It is a domain in which singlet and triplet kinetics both play an important role in determining the performance of various optoelectronic devices. Since triplet excitons are non-emissive, it brings further challenges in the understanding of triplet kinetics. In this work, we have studied the effect of polymer chain packing on triplet diffusion in the polyfluorene based polymeric system, which is known to give efficient organic light emitting diode (OLED) efficiency for display devices. Furthermore, this polyfluorene system exhibits an efficient triplet–triplet fusion process, which provides singlet excitons as delayed fluorescence and becomes a tool to study triplet exciton kinetics. We have developed a unique method to trace the position of the triplet exciton in the emissive layer of OLEDs by analyzing angle-resolved delayed electroluminescence emission patterns as a function of time. This study could provide exciton transport kinetics in the transverse direction from the substrate plane. Furthermore, direct visualization of the delayed photoluminescence imaging technique could provide lateral transport kinetics of triplet excitons. Results suggest that the diffusion is significantly anisotropic in thinner films. As the thickness of the film increases, anisotropy reduces in triplet transport. Moreover, we noticed that in thicker polymeric semiconductor films, diffusivity approaches close to ultrahigh 10−3 cm2 s−1, which is similar to the values that are reported for acene-based molecular crystalline thin films. Our results also provide important insight into efficient electroluminescence in unusually thick (1.2 μm) polyfluorene-based emissive layers of OLEDs.

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Abstract-This paper reports study of metal-oxide-semiconductor (MOS) capacitors with 2.2 nm dry and N O grown gate dielectrics. Interface trap generation during constant voltage stressing at different operating temperatures (from 22 C to 90 C) has been investigated. The effect of nitrogen annealing (20 min) at 400 C on high temperature stress-induced interface traps was also studied.Index Terms-Oxynitrides, SILC, temperature dependence of interface trap generation, ultra-thin oxides.

Quasi-Fermi-level (QFL) splitting is a direct measure of the open-circuit voltage (V_OC) in an optically illuminated semiconductor solar cell (SC). The evolution of QFL splitting under 1 sun illumination in...

Paramagnetic ions and radicals play essential roles in biology and medicine, but detecting them requires highly sensitive and ambient-operable sensors. Optically addressable spin color centers in 3D semiconductors are useful for detecting paramagnetic spins due to their sensitivity to spin magnetic noise. However, creating high-quality spin defects near the surface of 3D materials is challenging. Here, we show that spin qubits in hexagonal boron nitride (hBN), a layered van der Waals (vdW) material, can efficiently detect paramagnetic spins in liquids at nanoscales. We create shallow spin defects near the hBN surface, which maintain high-contrast optically detected magnetic resonance (ODMR) in liquids. Then, we detect paramagnetic ions in water using spin relaxation measurements, with a sensitivity of about 10 −18 mol/ for Gd 3+ ions. Finally, we show that paramagnetic ions reduce the contrast of spindependent fluorescence, enabling efficient detection by continuous wave ODMR. Our results demonstrate the potential of ultrathin hBN quantum sensors for chemical and biological applications.