Optimization of charge generation in polymer blends is crucial for the fabrication of highly efficient polymer solar cells. While the impacts of the polymer chemical structure, energy alignment, and interface on charge generation have been well studied, not much is known about the impact of polymer aggregation on charge generation. Here, we studied the impact of aggregation on charge generation using transient absorption spectroscopy, neutron scattering, and atomic force microscopy. Our measurements indicate that the 1,8-diiodooctane additive can change the aggregation behavior of poly(benzodithiophene-alt-dithienyl difluorobenzotriazole (PBnDT-FTAZ) and phenyl-C61-butyric acid methyl ester (PCBM)polymer blends and impact the charge generation process. Our observations show that the charge generation can be optimized by tuning the aggregation in polymer blends, which can be beneficial for the design of highly efficient fullerene-based organic photovoltaic devices.
Organometal halides are promising materials for photovoltaic applications, offering tunable electronic levels, excellent charge transport, and simplicity of thin-film device fabrication. Two-dimensional (2D) perovskites have emerged as promising candidates over three-dimensional (3D) ones due to their interesting optical and electrical properties. However, maximizing the power conversion efficiency is a critical issue to improve the performance of these solar cells. In this work, we studied the photophysics of a two-dimensional (2D) perovskite (CH3NH3)2Pb(SCN)2I2 thin film using steady-state and time-resolved absorption and emission spectroscopy and compared it with the three-dimensional (3D) counterpart CH3NH3PbI3. We observed a higher bandgap and faster charge recombination in (CH3NH3)2Pb(SCN)2I2 compared to CH3NH3PbI3. This work provides an improved understanding of fundamental photophysical processes in perovskite structures and provides the guideline for the design, synthesis, and fabrication of solar cells.
I. INTRODUCTION This report is a documentation, from inception in 1955 to termination in 1958, of the research and development program pertinent to the conceptual design and ultimate construction at Argonne of an advanced research reactor with a peak thermal flux of 5 x 10 n/(cm)(sec). More specifically, it describes the basic reactor complex, the problems involved, the various approaches pursued, the present status and estimated cost of the project, along with recommendations for future research and development essential to the successful culmination of the project. A preliminary design study of this reactor concept, identified as the Mighty Mouse Research Reactor, was published as ANL-5688.-'-The advanced research programs in the fields of chemistry, physics, and metallurgy, that would be facilitated in the environment provided by the Mighty Mouse Reactor are outlined in Appendix A.
Conjugated polymers and small molecules have been intensively studied due to their unique electronic and optical properties. Relatively easy and inexpensive fabrication, light weight, mechanical flexibility and non-toxic processing methods open broad prospects for their applications in solar cells[1, 2]. Power conversion efficiency of about 16% [3] has been achieved in these solar cells. Significant focus of research efforts involve develop new materials or to advance processing systems to increase the power conversion efficiency (PCE)[4, 5]. Currently, there remains a question whether the processing based on the nonhalogenated solvents, called "green solvents"[6], is possible on an industrial-scale. The sustainable manufacturing of these organic electronics, because of the organic solvents used, still pose serious health problems and a harmful environmental impact. Here, we studied the morphology of the "green solvents" processed polymer blend and compared with the blend processed with "halogenated solvent" to explore the reasons for the difference in charge generation efficiency in polymer solar cells based on aliphatic side chain and oligoethylene glycol (OEG) side chain[7]. The performance of the highly efficient PPDT2FBT:PCBM [8]system with 9.2% power conversion efficiency is degraded significantly to 1.4% when PCBO12 is blended with a OEG version of a polymer namely PPDT2FBT-A[9], that has only a minor side-chain modification. We employed Atomic Force Microscopy to investigate the impact of side chain on morphology of these polymer blends.
The newly emerged family of organic-inorganic halide perovskites not only revolutionizes the field of photovoltaic research with an average PCE > 20%; but also triggers plentiful studies on optical gain, light-emitting diodes, and field-field-transistors due to the tunability of optical and electrical properties brought by the versatility of organic chemistry synthesis. Most of the works focus on achieving a higher power conversion efficiency and/or light-emitting properties through a variety of chemical synthesis, novel growth conditions, and fabrication methods [1,2]. The solution-processed three-dimensional (3D) organic-inorganic halide perovskites have shown great promise as solar cells [1] due to high charge carrier mobility, long exciton diffusion length, and low concentration of traps, but their poor stability over longer periods of time due to heat, moisture, light, etc. has stopped them from becoming widely commercialized. However, two-dimensional perovskites (2D) have emerged as a replacement for the 3D perovskites, offering superior properties such as longer lifetime, more stability, higher bandgap, and versatility of organic chemistry synthesis [3][4][5][6][7]. However, the studies on the electronic structure and properties of 2D perovskite materials are very limited. Therefore, the investigation of optoelectronic properties in relation to chemical synthesis and morphological changes is critically important. In this work, we successfully synthesized deuterated methylammonium iodide (CH 3 ND 3 I) and prepared deuterated 2D perovskite (CH 3 ND 3 ) 2 Pb(SCN) 2 I 2 thin films and studied the impact of deuteration on morphological changes. X-ray diffraction (XRD) measurements were carried out for the structural characterization and scanning electron microscopy (SEM) was used for morphological characterization.
Lokta paper is a handmade paper indigenous to Nepal. The paper is made from inner fibrous bark of Lokta bushes; evergreen shrubs that grow in Himalayan forests ranging from 1600 to 4000 m. Because of its durability and resistance to bugs and moulds, the paper in its original or modified from is being used in official documents, calligraphy, holy books, packaging materials, and even to make paper bills [1]. The paper is fabricated in local levels following the traditional eco-friendly method of fiber processing. Firstly, outer scaly bark from raw fiber is manually removed and cut to small pieces and soaked in cold water for 5−6 hours. The biomass is boiled in water for around 5−10 hours and then washed with ash or alkali solution. The softened fiber biomass is beaten to make pulp and then dispersed to make slurry. The slurry is poured in a wooden mesh frame or paper moulds over a water tank. The frame is then drained and air dried to get paper sheet. Depending on the demand, the paper can be colored using natural dyes obtained from different plants and or patterned for artistic purposes. A systematic characterization of lokta paper sheet from material perspective, which helps to explain it novel properties, is missing in literature. In this work, we studied fiber organization, morphology and elemental distribution in lokta paper sheet with the help of scanning electron microscope (SEM) coupled to an electron probe micro analyzer (EPMA). For SEM imaging the paper sample was sputter coated with carbon and imaged in a JEOL field-emission JXA−8530F EPMA equipped with an SDD X-ray energydispersive spectrometer (EDS). Finally, we also did atomic force microscopy (AFM) imaging in tapping mode to explore surface roughness and structural details in the sample at nanoscopic level. AFM was performed at ambient condition in tapping mode. Finally, the X-ray diffraction (XRD) data were collected at Braggs' angle 2θ ranging from 5 to 40° by a X-ray diffractometer. The Cu Kα line (λ=1.540A°) was used as X-ray source. The SEM micrographs of lokta paper imaged at different magnification is shown are figure 1A-D. The micrographs show that in the paper the cellulosic fibers are randomly oriented so as to form densely packed interwoven networks (Figure 1 and B). It is known that strength of paper sheet is largely determined by strength of individual fiber and degree of cross linking within the individual fibers. The presence of long interconnecting fibers having no or low curl could provide durability and strength to the paper sheet. With further zooming individual fiber surface can be imaged (Figure 1C and D). We found fiber diameter in the range of 10−14 micrometer. In most of the fibers, individual micro-fibrils that run straight along the length of fiber are clearly visible (yellow dotted regions in Figure C and D). In some fibers gummy material is found attached on the surface (white dotted region in Figure 1C. The micro-fibrils are visible due to removal of gummy materials such as lignin and hemicellulose from the fiber surface ...
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