Methylammonium lead iodide (CH3NH3PbI3 or MAPI) is an organohalide lead perovskite, a promising material for optoelectronic application, e.g. in solar cells and photodetectors. It has a number of advantages over more traditional photovoltaics materials such as CIGS, GaAs, and even silicon due to facile solution processing, direct bandgap, high optical absorption, sufficiently high, balanced carrier mobilities, shallow trap defects and low-cost synthesis. At present moment there are number of article which reported measurement of second-harmonic generation in MAPI single crystals and presented contradictory results demonstrating the presence or absence of second-harmonic signal from MAPI. In this work, the second-harmonic generation (SHG) is observed in MAPI thin film that can be used as a base of high efficient solar sell.
The SHG intensity from MAPI is measured to be at least three orders of magnitude more than one from substrate and encapsulation glasses. The MAPI nonlinear second-order susceptibility is estimated as compared to reference sample of y-cut quartz. In case of bulk contribution, the MAPI second-order susceptibility of 10-15 m/V is achieved.
The polarization of SHG signal is experimentally studied in MAPI samples. The fraction of linearly polarized SHG signal is different for p- and s-polarization of fundamental wave and increases in case of p-polarized pump. The large non-polarized background of SHG signal is partly corresponded to SHG hyper-Rayleigh scattering. The hyper-Rayleigh scattering angle is experimentally estimated using the diaphragm behind the collimating objective lens and found to be less then 11 degrees.
Recently, bilayer resist processing combined with development in hydrofluoroether (HFE) solvents has been shown to enable single color structuring of vacuum-deposited state-of-the-art organic light-emitting diodes (OLED). In this work, we focus on further steps required to achieve multicolor structuring of <i>p-i-n</i> OLEDs using a bilayer resist approach. We show that the green phosphorescent OLED stack is undamaged after lift-off in HFEs, which is a necessary step in order to achieve RGB pixel array structured by means of photolithography. Furthermore, we investigate the influence of both, double resist processing on red OLEDs and exposure of the devices to ambient conditions, on the basis of the electrical, optical and lifetime parameters of the devices. Additionally, water vapor transmission rates of single and bilayer system are evaluated with thin Ca film conductance test. We conclude that diffusion of propylene glycol methyl ether acetate (PGMEA) through the fluoropolymer film is the main mechanism behind OLED degradation observed after bilayer processing.
Organic electronics has recently gained attention as a new field promising cheaper, flexible, and large-scale
devices. Although photolithography has proven to be a high-resolution and high-throughput patterning method with
excellent registration capabilities, the emerging field of organic electronics has been largely unsuccessful in adapting this
well-established method as a viable approach to patterning. Chemical compatibility issues between organic materials and
the processing solvents and chemicals required by photolithography have been the main problem. This challenge has led
us to identify a set of non-damaging processing solvents and to develop alternative imaging materials in order to extend
photolithographic patterning methods to organic electronics.
We have identified supercritical carbon dioxide and hydrofluoroether (HFE) solvents as chemically benign to
organic electronic materials and which are also suitable as processing solvents. We refer to these solvents as orthogonal
in that they do not substantially interact with traditional aqueous and organic solvents. Multi-layered devices are easily
realized by exploiting this orthogonality property; subsequent layers are deposited and patterned without damaging or
otherwise adversely affecting previously deposited underlying layers. We have designed and synthesized novel
photoresists, which are processible in these benign solvents.
We report the observation of cathodoluminescence (CL) of organic multilayers of tris-(8-hydroxyquinoline) aluminium (Alq3) and 2- (4biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) deposited on ITO-coated glass, with and without hole transport layer and compare it with electroluminescence (EL) from similar devices. Excitation of the CL of such multilayer organic anodes was accomplished by low energy electrons field emitted by single walled carbon nanotube
cathodes. The dependence of CL spectrum and intensity on voltage (V), current (I), type of transport layer and the cathode-anode geometry has been studied. We propose carbon nanotubes as efficient cathodes for stable CL emission from multi-layer anodes at small cathode-anode separations. The role of hole-transport layer is also discussed.
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