Engineering topics

Xue, Jiangeng

Publications and source records attributed to Xue, Jiangeng.

10 records

DOE OSTI2018

Thin film photovoltaic devices with microlens arrays

Textured transparent layers are formed on the incident light receiving surface of thin film solar cells to increase their efficiency by altering the incident light path and capturing a portion of the light reflected at the MLA. The textured transparent layer is an array of lenses of micrometer proportions such as hemispheres, hemi-ellipsoids, partial-spheres, partial-ellipsoids, cones, pyramids, prisms, half cylinders, or combinations thereof. A method of forming the textured transparent layer to the light incident surface of the solar cell is by forming an array of lenses from a photocurable resin and its subsequent curing. The photocurable resin can be applied by inkjet printing or can be applied by roll to roll imprinting or stamping with a mold.

14 SOLAR ENERGY↗

DOE OSTI2018

Final Scientific/Technical Report -- Single-Junction Organic Solar Cells with >15% Efficiency

Organic solar cells have the potential to offer low-cost solar energy conversion due to low material costs and compatibility with low-temperature and high throughput manufacturing processes. This project aims to further improve the efficiency of organic solar cells by applying a previously demonstrated molecular self-assembly approach to longer-wavelength light-absorbing organic materials. The team at the University of Florida designed and synthesized a series of low-bandgap organic semiconductors with functional hydrogen-bonding groups, studied their assembly characteristics and optoelectronic properties in solid-state thin film, and fabricated organic solar cells using solution processing. These new organic materials absorb light up 800 nm wavelength, and provide a maximum open-circuit voltage of 1.05 V in the resulted solar cells. The results further confirmed the effectiveness in this approach to guide the assembly of organic semiconductors in thin films to yield higher photovoltaic performance for solar energy conversion. Through this project, we have gained important understanding on designing, synthesizing, and processing organic semiconductors that contain appropriately functionalized groups to control the morphology of the organic photoactive layer in solar cells. Such fundamental knowledge could be used to further develop new functional organic materials to achieve higher photovoltaic performance, and contribute to the eventual commercialization of the organic solar cell technology.

14 SOLAR ENERGY↗

DOE OSTI2017

Thin film organic photodetectors for indirect X-ray detection demonstrating low dose rate sensitivity at low voltage operation

Here, developments in the field of organic semiconductors have generated organic photodetectors with high quantum efficiency, wide spectral sensitivity, low power consumption, and unique form factors that are flexible and conformable to their substrate shape. In this work, organic photodetectors coupled with inorganic CsI(Tl) scintillators are used to showcase the low dose rate sensitivity that is enabled when high performance organic photodetectors and scintillator crystals are integrated. The detection capability of these organic-inorganic coupled systems to high energy radiation highlights their potential as an alternative to traditional photomultiplier tubes for nuclear spectroscopy applications. When exposed to Bremsstrahlung radiation produced from an X-ray generator, SubPc:C 60 , AlPcCl:C 70 , and P3HT:PC 61 BM thin film photodetectors with active layer thicknesses less than 100 nm show detection of incident radiation at low and no applied bias. Remarkably low dose rates, down to at least 0.28 µGy/s, were detectable with a characteristic linear relationship between exposure rate and photodetector current output. These devices also demonstrate sensitivities as high as 5.37 mC Gy -1 cm -2 when coupled to CsI(Tl). Additionally, as the tube voltage across the X-ray generator was varied, these organic-inorganic systems showed their ability to detect a range of continuous radiation spectra spanning several hundred keV.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Air stable organic-inorganic nanoparticles hybrid solar cells

A solar cell includes a low work function cathode, an active layer of an organic-inorganic nanoparticle composite, a ZnO nanoparticle layer situated between and physically contacting the cathode and active layers; and a transparent high work function anode that is a bilayer electrode. The inclusion of the ZnO nanoparticle layer results in a solar cell displaying a conversion efficiency increase and reduces the device degradation rate. Embodiments of the invention are directed to novel ZnO nanoparticles that are advantageous for use as the ZnO nanoparticle layers of the novel solar cells and a method to prepare the ZnO nanoparticles.

14 SOLAR ENERGY↗

DOE OSTI2015

High efficiency organic photovoltaic cells employing hybridized mixed-planar heterojunctions

A device is provided, having a first electrode, a second electrode, and a photoactive region disposed between the first electrode and the second electrode. The photoactive region includes a first photoactive organic layer that is a mixture of an organic acceptor material and an organic donor material, wherein the first photoactive organic layer has a thickness not greater than 0.8 characteristic charge transport lengths; a second photoactive organic layer in direct contact with the first organic layer, wherein the second photoactive organic layer is an unmixed layer of the organic acceptor material of the first photoactive organic layer, and the second photoactive organic layer has a thickness not less than about 0.1 optical absorption lengths; and a third photoactive organic layer disposed between the first electrode and the second electrode and in direct contact with the first photoactive organic layer. The third photoactive organic layer is an unmixed layer of the organic donor layer of the first photoactive organic layer and has a thickness not less than about 0.1 optical absorption lengths.

14 SOLAR ENERGY↗

DOE OSTI2015

Enhancement in Organic Photovoltaic Efficiency through the Synergistic Interplay of Molecular Donor Hydrogen Bonding and -Stacking

For organic photovoltaic (OPV) cells based on the bulk heterojunction (BHJ) structure, it remains challenging to rationally control the degree of phase separation and percolation within blends of donors and acceptors to secure optimal charge separation and transport. Reported is a bottom-up, supramolecular approach to BHJ OPVs wherein tailored hydrogen bonding (H-bonding) interactions between π-conjugated electron donor molecules encourage formation of vertically aligned donor π-stacks while simultaneously suppressing lateral aggregation; the programmed arrangement facilitates fine mixing with fullerene acceptors and efficient charge transport. The approach is illustrated using conventional linear or branched quaterthiophene donor chromophores outfitted with terminal functional groups that are either capable or incapable of self-complementary H-bonding. When applied to OPVs, the H-bond capable donors yield a twofold enhancement in power conversion efficiency relative to the comparator systems, with a maximum external quantum efficiency of 64%. H-bond promoted assembly results in redshifted absorption (in neat films and donor:C 60 blends) and enhanced charge collection efficiency despite disparate donor chromophore structure. Both features positively impact photocurrent and fill factor in OPV devices. Film structural characterization by atomic force microscopy, transmission electron microscopy, and grazing incidence wide angle X-ray scattering reveals a synergistic interplay of lateral H-bonding interactions and vertical π-stacking for directing the favorable morphology of the BHJ.

14 SOLAR ENERGY↗

DOE OSTI2015

Stable and all solution processable quantum dot light-emitting diodes

Embodiments of the invention are directed to quantum dot light emitting diodes (QD-LEDs) where the electron injection and transport layer comprises inorganic nanoparticles (I-NPs). The use of I-NPs results in an improved QD-LED over those having a conventional organic based electron injection and transport layer and does not require chemical reaction to form the inorganic layer. In one embodiment of the invention the hole injection and transport layer can be metal oxide nanoparticles (MO-NPs) which allows the entire device to have the stability of an all inorganic system and permit formation of the QD-LED by a series of relatively inexpensive steps involving deposition of suspensions of nanoparticles and removing the suspending vehicle.

Qian, Lei↗

DOE OSTI2014

Balancing high gain and bandwidth in multilayer organic photodetectors with tailored carrier blocking layers

We present detailed studies of the high photocurrent gain behavior in multilayer organic photodiodes containing tailored carrier blocking layers we reported earlier in a Letter [W. T. Hammond and J. Xue, Appl. Phys. Lett. 97, 073302 (2010)], in which a high photocurrent gain of up to 500 was attributed to the accumulation of photogenerated holes at the anode/organic active layer interface and the subsequent drastic increase in secondary electron injection from the anode. Here, we show that both the hole-blocking layer structure and layer thickness strongly influence the magnitude of the photocurrent gain. Temporal studies revealed that the frequency response of such devices is limited by three different processes with lifetimes of 10 μs, 202 μs, and 2.72 ms for the removal of confined holes, which limit the 3 dB bandwidth of these devices to 1.4 kHz. Furthermore, the composition in the mixed organic donor-acceptor photoactive layer affects both gain and bandwidth, which is attributed to the varying charge transport characteristics, and the optimal gain-bandwidth product is achieved with approximately 30% donor content. Finally, these devices show a high dynamic range of more than seven orders of magnitude, although the photocurrent shows a sublinear dependence on the incident optical power.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2013

High efficiency organic photovoltaic cells employing hybridized mixed-planar heterojunctions

A device is provided, having a first electrode, a second electrode, and a photoactive region disposed between the first electrode and the second electrode. The photoactive region includes a first organic layer comprising a mixture of an organic acceptor material and an organic donor material, wherein the first organic layer has a thickness not greater than 0.8 characteristic charge transport lengths, and a second organic layer in direct contact with the first organic layer, wherein: the second organic layer comprises an unmixed layer of the organic acceptor material or the organic donor material of the first organic layer, and the second organic layer has a thickness not less than about 0.1 optical absorption lengths. Preferably, the first organic layer has a thickness not greater than 0.3 characteristic charge transport lengths. Preferably, the second organic layer has a thickness of not less than about 0.2 optical absorption lengths. Embodiments of the invention can be capable of power efficiencies of 2% or greater, and preferably 5% or greater.

14 SOLAR ENERGY↗

DOE OSTI2012

Very High Efficiency, Hybrid Organic-Inorganic Photovoltaic Cells

This SETP project focuses on developing highly efficient, hybrid organic inorganic photovoltaic (OIPV) cells. The goal is to greatly enhance the power conversion efficiency of hybrid OIPV cells using several innovative approaches. The specific objectives are: (i) to develop new inorganic nanocrystals along with conjugated oligomers and polymers to improve their matching with the solar spectrum; (ii) to engineer the interfacial electronic structures at the hybrid interface to minimize energy and carrier losses during charge transfer; (iii) to understand the assembly of hybrid polymer/nanorod composites and demonstrate hybrid nanostructures that facilitate carrier transport and collection; and (iv) to demonstrate high efficiency hybrid OIPV cells by effectively incorporating materials absorbing in different spectral regions. Through this project, the research team at the University of Florida synthesized a series of new functional organic materials and colloidal nanocrystals with optical absorption covering the near-ultraviolet, visible, and near-infrared regions of the solar spectrum. The team also demonstrated improved understandings on how to control the morphological structure of the organic/inorganic hybrid active layer as well as on the orientation of anisotropic nanostructures in the organic matrix. With the demonstration of several innovative device structures, the efficiency of such hybrid photovoltaic cells was drastically increased. The introduction of proper chemical treatment of the nanocrystal/organic interface and the demonstration of a new light trapping technique (which can also be easily scaled up for large area device fabrication) also contributed to the significant increase in device efficiency. The new knowledge on material synthesis, material processing, device physics, and optical design gained from this project will greatly contribute to the further development of this low-cost PV technology.

14 SOLAR ENERGY↗