3D pitch rotation of microparticles and cells assumes importance in a wide variety of applications in biology, physics, chemistry and medicine. Applications such as cell imaging and injection benefit from pitch-rotational manipulation. Generation of such motion in single beam optical tweezers has remained elusive due to complicacies of generating high enough ellipticity perpendicular to the direction of propagation. Further, trapping an extended object at two locations can only generate partial pitch motion by moving one of the foci in the axial direction. Here, we use hexagonal-shaped upconverting particles and single cells trapped close to a goldcoated glass cover slip in a sample chamber to generate complete 360 degree and continuous pitch motion even with a single optical tweezers beam. The tweezers beam passing through the gold surface is partially absorbed and generates a hot-spot to produce circulatory convective flows in the vicinity which rotates the objects. The rotation rate can be controlled by the intensity of the laser light and the thickness of the gold layer. Thus such a simple configuration can turn the particle in the pitch sense. The circulatory flows in this technique have a diameter of about 5 µm which is smaller than those reported using acousto-fluidic techniques.
Perovskite materials with ABX3 chemistries are promising candidates for photovoltaic applications, owing to their suitable optoelectronic properties. However, they are highly hydrophilic and unstable in nature, limiting the commercialization of perovskite photovoltaics. Mixed halide ion-doped perovskites are reported to be more stable compared to simple ABX3 chemistries. This paper describes ab initio modeling, synthesis, and characterization of thiocyanate doped lead iodide CH3NH3PbI(3−x)(SCN)x perovskites. Several perovskite chemistries with an increasing concentration of (SCN)− at x = 0, 0.25, 0.49, 1.0, 1.45 were evaluated. Subsequently, ‘n-i-p’ and ‘p-i-n’ perovskite solar device architectures, corresponding to x = 0, 0.25, 0.49, 1.0 thiocyanate doped lead halide perovskite chemistry were fabricated. The study shows that among all the devices fabricated for different compositions of perovskites, p-i-n perovskite solar cell fabricated using CH3NH3PbI(3−x)(SCN)x perovskite at x = 1.0 exhibited the highest stability and device efficiency was retained until 450 h. Finally, a solar panel was fabricated and its stability was monitored.
Whether organic semiconductors, in their pristine form, are inherently intrinsic or involuntarily doped is an open question that is yet to be addressed. In this work, the source of charge carriers within pristine organic semiconductors, processed in a controlled inert ambience, is investigated using organic metal− insulator−metal capacitor (OMISCAP) devices. Top-gate and bottom-gate architecture of OMISCAP devices based on various organic semiconductors along with different combinations of metal−semiconductor junctions are demonstrated. The impact of the metal−semiconductor junction and the semiconductor thickness on the capacitance−voltage (C−V) characteristics of MISCAP devices is studied to ensure the role of contact-induced charge injection into the semiconductor, contrary to involuntary doping as the source of charge. The charge injection from the metal to the semiconductor is found to be the predominant source of charge carriers inside a pristine organic semiconductor rather than inadvertent doping. The findings in this report are further substantiated using TCAD device simulation.
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