Organic photovoltaics will become 30 years old relatively soon. In spite of the impressive development achieved throughout these years, especially in terms of reported power conversion efficiencies, there are still important technological and fundamental obstacles to circumvent before they can be implemented into reliable and long-lasting applications. Regarding device processing, the synthesis of highly soluble polymeric semiconductors first, and fullerene derivatives then, was initially considered as an important breakthrough that would definitely change the fabrication of photovoltaics once for all. Nowadays, the promise of printing solar cells by low-cost and high throughput mass production techniques still stands. However, the potential and the expectation raised by this technology is such that it is considerably difficult to keep track of the most significant progresses being now published in different and even monographic journals. There is therefore the need to compile the most remarkable advances in well-documented reviews than can be used as a reference for future ideas and works. In this letter, we review the development of polymeric solar cells from its origin to the most efficient devices published to date. After analyzing their fundamental limits, we separate these achievements into three different categories traditionally followed by the scientific community to push devices over 10% power conversion efficiency: Active materials, strategies -fabrication/processing procedures- that can mainly modify the active film morphology and result in improved efficiencies for the same starting materials, and all the different cell layout/architectures that have been used in order to extract as high photocurrent as possible from the Sun. The synthesis of new donors and acceptors, the use of additives and post-processing techniques, buffer interlayers, inverted and tandem designs are some of the most important aspects that are in detailed reviewed in this letter. All have equally contributed to develop this technology and leave it at doors of commercialization. (C) 2015 Elsevier B.V. All rights reserved.
The past decades have driven a great deal of interest for developing low-cost electroluminescent devices. In this aim, highly emissive phosphors based on Earth-abundant metals and presenting the advantage of environment-benignancy are actively researched. Based on these requirements, copper(I) complexes have been identified as favorable candidates that could advantageously replace the well-established iridium(III) complexes. (C) 2015 Elsevier B.V. All rights reserved.
The mobility is an important parameter for organic solar cell materials as it influences the charge extraction and recombination dynamics. In this study, the time of flight technique is used to investigate the charge mobility of the important organic photovoltaic materials PC71BM, PTB7 and their blend. The electron mobility of PC71BM is in the region of 1 x 10(-3) cm(2)/Vs for the neat fullerene film, and has a positive electric field dependence. At room temperature the hole mobility of PTB7 is 1 x 10(-3) cm(2)/Vs for the neat film and 2 x 10(-4) cm(2)/Vs for their blend. The hole mobility of the blend reduces by a factor of a thousand when the sample is cooled from room temperature to 77 K. This finding is compared with the device performance of efficient PTB7:PC71BM solar cells for varying temperature. At 77 K the solar cell efficiency halved, due to losses in fill factor and short circuit current. Bimolecular and trap-assisted recombination increase at low mobility (low temperature) conditions, whereas at high mobility conditions the open circuit voltage reduces. The power conversion efficiency as a function of temperature has a maximum between 260 K and 295 K, revealing an optimized mobility at room temperature. (C) 2015 The Authors. Published by Elsevier B.V.
Flexible and wearable energy storage devices are strongly demanded to power smart textiles. Herein, reduced graphene oxide (RGO) and polypyrrole (PPy) were deposited on cotton fabric via thermal reduction of GO and chemical polymerization of pyrrole to prepare textile-based electrodes for supercapacitor application. The obtained PPy-RGO-fabric retained good flexibility of textile and was highly conductive, with the conductivity of 1.2 S cm(-1). The PPy-RGO-fabric supercapacitor showed a specific capacitance of 336 F g(-1) and an energy density of 21.1 Wh kg(-1) at a current density of 0.6 mA cm(-2). The RGO sheets served as conductor and framework under the PPy layer, which could facilitate electron transfer between RGO and PPy and restrict the swelling and shrinking of PPy, thus resulting in improved electrochemical properties respect to the PPy-fabric device. (C) 2015 Elsevier B.V. All rights reserved.
Highly efficient and non-hysteresis organic/perovskite planar heterojunction solar cells was fabricated by low-temperature, solution-processed method with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al. The high-quality perovskite thin film was obtained using a solvent-induced-fast-crystallization deposition involving spin-coating the CH3NH3PbI3 solution followed by top-dropping chlorobenzene with an accurate control to induce the crystallization, which results in highly crystalline, pinhole-free, and smooth perovskite thin film. Furthermore, it was found that the molar ratio of CH3NH3I to PbI2 greatly influence the properties of CH3NH3PbI3 film and the device performance. The equimolar or excess PbI2 was facile to form a flat CH3NH3PbI3 film and produced relatively uniform perovskite crystals. Perovskite solar cells (PSCs) with high-quality CH3NH3PbI3 thin film showed good performance and excellent repeatability. The power conversion efficiency (PCE) up to 13.49% was achieved, which is one of the highest PCEs obtained for low-temperature, solution-processed planar perovskite solar cells based on the structure ITO/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al. More importantly, PSCs fabricated using this method didn't show obvious hysteresis under different scan direction and speed. (C) 2015 Elsevier B.V. All rights reserved.
Polymer light emitting diodes (PLEDs) have attracted a great deal of interest within academia and industry because of their potential applications in flat panel displays and solid-state lighting technologies. The solution processability of polymers offers the advantages of simple and mild fabrication conditions enabling to cut cost and produce large area displays. Among all polymeric hosts under investigation, carbazole-based materials benefit from the wide bandgap of carbazole as well as its remarkable thermal, photochemical and chemical stability. Especially, the relatively high triplet energy level of carbazole makes it an appealing candidate to design hosts for wide bandgap triplet emitters such as blue dopants. In this review, an overview of all carbazole-based polymeric hosts reported to date is presented. Noticeably, easiness of synthesis has been an aspect largely developed to access to these polymeric structures. (C) 2015 Elsevier B.V. All rights reserved.
Solution processed CH3NH3PbIxCl3-x based planar heterojunction perovskite solar cells with power conversion efficiency (PCE) above 14% are reported. The devices benefit from a phenyl-C-61-butyric acid methyl ester (PCBM)/ZnO double electron transport layer (ETL) as well as a short air-aging step. The role of the additional ZnO ETL is studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectroscopy (SIMS). Apart from improving the energy level alignment, the ZnO layer blocks the reactions between the metal electrode and perovskite components, increasing the air stability of the device. A crucial step in our processing is a short air-aging step for the device, which significantly increases the device performance by reducing the recombination process. Since the ZnO nanoparticle layer requires no thermal annealing, the maximum temperature to fabricate the device can be kept below 100 degrees C, making this structure compatible with roll-to-roll processing on plastic films. (C) 2015 Elsevier B.V. All rights reserved.
Polypyrrole (PPy)-tungsten oxide (WO3) hybrid nanocomposite have been successfully synthesized using different weight percentages of tungsten oxide (10-50%) dispersed in polypyrrole matrix by solid state synthesis method. The sensor based on PPy-WO3 was fabricated on glass substrate using cost effective spin coating method for detection of NO2 gas in the low concentration range of 5-100 ppm. The gas sensing performance of hybrid material was studied and compared with those of pure PPy and WO3. It was found that PPy-WO3 hybrid nanocomposite sensor can complement the drawbacks of pure PPy and WO3. The structure, morphology and surface composition properties of PPy-WO3 hybrid nanocomposites were employed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The presence of WO3 in PPy matrix and their interaction was confirmed using XRD, FTIR techniques. The porous surface morphology was observed with addition of WO3 in PPy matrix which is useful morphology for gas sensing applications. TEM image of PPy-WO3 hybrid nanocomposites shows the average diameter of 80-90 nm. X-ray photoelectron spectroscopy (XPS) was used to characterize the chemical composition of nanocomposites. It was observed that 50% WO3 loaded PPy sensor operating at room temperature exhibit maximum response of 61% towards 100 ppm of NO2 gas and able to detect low concentration of 5 ppm NO2 gas with reasonable response of 8%. The hybrid sensor shows better sensitivity, selectivity, reproducibility and stability compared to pure PPy and WO3. The proposed sensing mechanism of hybrid nanocomposite in presence of air and NO2 atmosphere was discussed with the help of energy band diagram. Furthermore, the interaction of NO2 gas with PPy-WO3 hybrid nanocomposites sensor was studied by cole-cole plot using impedance spectroscopy. (C) 2014 Elsevier B.V. All rights reserved.
We report fully vacuum-processed perovskite solar cells with high open circuit voltage. All the layers in the solar cells including the perovskite active layer, hole extraction layers and electron extraction layers were deposited in the vacuum process. Use of molybdenum oxide (MoO3) as an interfacial layer and N, N'-Di(1-naphthyl)-N, N'-diphenyl-(1,1'-biphenyl)- 4,4'-diamine (NPB) as a hole transport material (HTM) for hole extraction resulted in a high open circuit voltage (V-OC) of 1.12 V. Due to the effective hole extraction and high VOC, the devices showed a maximum power conversion efficiency (PCE) of 13.7%. The vacuum processed perovskite solar cells showed relatively high reproducibility showing the average value of PCE of 11.1%. (C) 2014 Elsevier B.V. All rights reserved.
Perovskite solar cells (PSCs) with a simple device structure are particularly attractive due to their low cost and convenient fabrication process. Herein, highly efficient, electron-blocking layer (EBL)-free planar heterojunction (PHJ) PSCs with a structure of ITO/CH3NH3PbI3/PCBM/Al were fabricated via low-temperature, solution-processed method. The power conversion efficiency (PCE) of over 11% was achieved in EBL-free PHJ-PSCs, which is closed to the value of PSC devices with the PEDOT:PSS as the EBL. It is impressed that the open-circuit voltage (V-oc) up to 1.06 V, an average value of 1.0 V for 43 devices, was obtained in EBL-free PHJ-PSCs. The electrochemical impedance spectroscopy (EIS) results suggested that the high PCE and Voc are attributed to the relatively large recombination resistance and low contact resistance in EBL-free PHJ-PSCs. The solution-processed, EBL-free PHJ structure paves a boulevard for fabricating high-efficiency and low-cost PSCs. (C) 2015 Elsevier B.V. All rights reserved.
Wearable energy storage devices that can be used in the garment industry are strongly required to power E-textiles. In this article, polypyrrole (PPy) nanorods were deposited on cotton fabrics via in situ polymerization of pyrrole in the presence of the fibrillar complex of FeCl3 and methyl orange as a reactive self-degraded template. The obtained fabrics could be directly used as supercapacitor electrodes, with a maximum specific capacitance of 325 F g(1) and an energy density of 24.7 Wh kg(1) at a current density of 0.6 mA cm(2). The capacitance remained higher than 200 F g(1) after 500 cycles. (C) 2015 Elsevier B. V. All rights reserved.
We investigate the electronic transport properties in molecular devices consisting of two phenyl-rings connected by Co and N atoms by using nonequilibrium Green's function method and density function theory. The molecule is coupled to two zigzag graphene nanoribbon electrodes. It is found that giant magnetoresistance effect exists in both the coplanar and the perpendicular conformations at low biases. And the total current decreases a lot, on order of 100, when the orientation of the phenyl ring changes from coplanar site to perpendicular site. This indicates a molecular switcher via conformational control. What's more, perfect dual spin-filtering effect and rectifying behavior can be realized by modulating the external magnetic field. So a multi-functional device is achieved in our designed molecular junction. Detailed explanations via transmission spectra, distribution of molecular projected self-consistent Hamiltonian states are given to the above useful phenomenon. (C) 2015 Elsevier B.V. All rights reserved.
Efficient deep-blue fluorescent emitters are of particular significance in organic light-emitting devices (OLEDs). An ambipolar deep-blue emitter, 4,4'-bis(4-(1-(4-(tert-butyl) phenyl)-1H- phenanthro[9,10-d] imidazol-2-yl)phenyl)-1,1'-binaphthalene (2NBTPI), was designed, synthesized and applied in a high-efficiency deep-blue emitting OLED. By modifying with binaphthyl, 2NBTPI exhibits a high thermal stability, deep blue emission as well as spatially separated HOMO and LUMO orbits. Comparing with its mononaphthyl counterpart 1,4-bis(4-(1-(4-(tert-butyl) phenyl)-1H-phenanthro[9,10-d] imidazol-2-yl) phenyl) naphthalene (NBTPI), 2NBTPI shows more balanced charge transport properties, better color purity (color index: (0.15, 0.09) versus (0.15, 0.11)), higher external quantum efficiency (EQE) (5.95% versus 5.73%) and slower efficiency roll-off (EQE roll-off at 100 mA cm(-2): 13.1% versus 27.6%). To the best of our knowledge, OLED performances of 2NBTPI are comparable to the best reported non-doped deep-blue emitters. (C) 2014 Elsevier B.V. All rights reserved.
In this contribution we show a simple approach for the development of all-polymer based complementary logic circuits fabricated by printing on plastic, at low temperature and in ambient conditions. This is achieved by patterning, with a bottom-up approach, solely synthetic carbon-based materials, thus incorporating earth-abundant elements and enabling in perspective the recycling - a critical aspect for low-cost, disposable electronics. Though very simple, the approach leads to logic stages with a delay down to 30 mu s, the shortest reported to date for all-polymer circuits, where each single component has been printed. Moreover, our circuits combine bendability and high transparency, favoring the adoption in several innovative applications for portable and wearable large-area electronics. (C) 2015 Elsevier B.V. All rights reserved.
Silver nanowire (AgNW) based transparent electrodes are inherently coarse and therefore typically are only ever weakly bonded to a substrate. A remarkable improvement in the characteristics of a AgNW network film has, however, been achieved through a simple and short process of irradiating it with intense pulsed light (IPL). This not only avoids any severe deterioration in the optical characteristics of the AgNW film, but also significantly improves its electrical conductivity, adhesion to a polymeric substrate, and ability to endure bending stress. Most important of all, however, is the finding that the surface roughness of AgNW networks can also be improved by radiation. In a series of measurements made of organic light emitting diodes fabricated using these treated electrodes, it was revealed that the leakage current can be notably reduced by IPL treatment. (C) 2014 Elsevier B.V. All rights reserved.
Aggregation-induced emission (ATE) type thermally activated delayed fluorescent (TADF) emitters were developed by asymmetric substitution of donor moieties to a diphenylsulfone acceptor. The AIE properties of the TADF emitters increased the quantum efficiency of the non-doped TADF devices and asymmetric substitution was more effective than symmetric substitution to enhance the quantum efficiency of the non-doped devices. (C) 2015 Elsevier B.V. All rights reserved.
Poly(3,4-ethylenedioxythiophene)-tosylate-polyethylene glycol-polypropylene glycol-polyethylene glycol (PEDOT-Tos-PPP) films were prepared via a vapor phase polymerization (VPP) method. The films possess good electrical conductivity (1550 S cm(-1)), low Seebeck coefficient (14.9 mu V K-1) and thermal conductivity (0.501Wm-1 K-1), and ZT similar to 0.02 at room temperature (RT, 295 K). Then, the films were treated with NaBH4/DMSO solutions of different NaBH4 concentrations to adjust the redox level. After the NaBH4/DMSO treatment (dedoping), the electrical conductivity of the films continuously decreased from 1550 to 5.7 S cm(-1), whereas the Seebeck coefficient steeply increased from 14.9 to 143.5 mu V K-1. A maximum power factor of 98.1 mu Wm(-1) K-2 has been achieved at an optimum redox level. In addition, the thermal conductivity of the PEDOT-Tos-PPP films decrease from 0.501 to 0.451Wm(-1) K-1 after treated with 0.04% NaBH4/DMSO solution. A maximum ZT value of 0.064 has been achieved at RT. The electrical conductivity and thermal conductivity (Seebeck coefficient) of the untreated and 0.04% NaBH4/DMSO treated PEDOT-Tos-PPP films decrease (increases) with increasing temperature from 295 to 385 K. And the power factor of the films monotonically increases with temperature. The ZT at 385 K of the 0.04% NaBH4/DMSO treated film is 0.155. (C) 2014 Elsevier B.V. All rights reserved.
We investigate the effect of boundary types on the rectifying behaviors in heterojunction composed of zigzag graphene and hexagonal boron-nitride (BNC) hybridized nanoribbons by employing nonequilibrium Green's functions in combination with the density-functional theory. The results demonstrate that the rectifying behavior is strongly dependent on the boundary types, while little affected by the width of BNC hybridized nanoribbons. It is noteworthy that the maximum rectifying ratio of the system at finite bias can be high up to orders of 107 in which atoms carbon in graphene nanoribbon are totally connected with atoms nitrogen in boron-nitride nanoribbon. The mechanism is proposed for these phenomena. (C) 2015 Elsevier B.V. All rights reserved.
We investigate the effect of boundary types on the rectifying behaviors in heterojunction composed of zigzag graphene and hexagonal boron-nitride (BNC) hybridized nanoribbons by employing nonequilibrium Green's functions in combination with the density-functional theory. The results demonstrate that the rectifying behavior is strongly dependent on the boundary types, while little affected by the width of BNC hybridized nanoribbons. It is noteworthy that the maximum rectifying ratio of the system at finite bias can be high up to orders of 10.sup.7 in which atoms carbon in graphene nanoribbon are totally connected with atoms nitrogen in boron-nitride nanoribbon. The mechanism is proposed for these phenomena.
Elementary perceptron is an artificial neural network with a single layer of adaptive links and one output neuron that can solve simple linearly separable tasks such as invariant pattern recognition, linear approximation, prediction and others. We report on the hardware realization of the elementary perceptron with the use of polyaniline-based memristive devices as the analog link weights. An error correction algorithm was used to get the perceptron to learn the implementation of the NAND and NOR logic functions as examples of linearly separable tasks. The physical realization of an elementary perceptron demonstrates the ability to form the hardware-based neuromorphic networks with the use of organic memristive devices. The results provide a great promise toward new approaches for very compact, low-volatile and high-performance neurochips that could be made for a huge number of intellectual products and applications. (C) 2015 Elsevier B.V. All rights reserved.