Showing papers by "Alan J. Heeger published in 2015"
TL;DR: This research presents a new generation of Bio-Inspired Smart Interfacial Science and Technology Materials and Devices for Multidisciplinary Science, developed by the team of Prof. J. Heeger and Prof. Y. Sun at Beihang University, Beijing.
Abstract: Prof. L. Huo, T. Liu, Prof. X. Sun, Y. Cai, Prof. Y. Sun Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education Beijing Key Laboratory of Bio-Inspired Energy Materials and Devices School of Chemistry and Environment Beihang University Beijing 100191 , P. R. China E-mail: sunym@buaa.edu.cn Prof. L. Huo, T. Liu, Prof. X. Sun, Y. Cai, Prof. A. J. Heeger, Prof. Y. Sun Heeger Beijing Research and Development Center International Research Institute for Multidisciplinary Science Beihang University Beijing 100191 , P. R. China
476 citations
TL;DR: Two identical bulk heterojunctions are connected in series using novel interconnection layers combining pH-neutral conjugated polyelectrolytes and a thin film of ZnO nanoparticles by a solution process to achieve the best performing tandem cells.
Abstract: Rational materials design and interface engineering are both essential to realize a high performance for tandem cells. Two identical bulk heterojunctions are connected in series using novel interconnection layers combining pH-neutral conjugated polyelectrolytes and a thin film of ZnO nanoparticles by a solution process. The best performing tandem cells achieve a power conversion efficiency of 11.3%, with 25% enhancement in efficiency compared with single cells, which arises primarily from the increased light absorption.
409 citations
TL;DR: 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.
Abstract: The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm(2) V(-1) s(-1). Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m(-2) and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.
378 citations
TL;DR: Small-bandgap polymer solar cells with a thick bulk heterojunction film of 340 nm exhibit high power conversion efficiencies due to maximized light absorption by the thick active layer and minimized recombination by the optimized lateral and vertical morphology through the processing additive.
Abstract: Small-bandgap polymer solar cells (PSCs) with a thick bulk heterojunction film of 340 nm exhibit high power conversion efficiencies of 9.40% resulting from high short-circuit current density (JSC ) of 20.07 mA cm(-2) and fill factor of 0.70. This remarkable efficiency is attributed to maximized light absorption by the thick active layer and minimized recombination by the optimized lateral and vertical morphology through the processing additive.
293 citations
TL;DR: This work demonstrates that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer exhibit a device efficiency of over 12% and improved device stability in air and is the first report on the use of an organic hole transport material that enables the formation of uniform perovkite films with complete surface coverage.
Abstract: Organic–inorganic hybrid perovskite materials offer the potential for realization of low-cost and flexible next-generation solar cells fabricated by low-temperature solution processing. Although efficiencies of perovskite solar cells have dramatically improved up to 19% within the past 5 years, there is still considerable room for further improvement in device efficiency and stability through development of novel materials and device architectures. Here we demonstrate that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer (instead of acidic PEDOT:PSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative to PEDOT:PSS, this work is the first report on the use of an organic hole transport material that enables the formation of uniform perovskite films with complete surface coverage and the demonstration of efficient, stable perovskite/fullerene planar heterojunction solar cells.
274 citations
TL;DR: Ultrafast Förster resonance energy transfer in a polymer-polymer system that significantly improves the power conversion efficiency in bulk heterojunction polymer solar cells from 6.8% to 8.9% is demonstrated, thus paving the way to achieving 15% efficient solar cells.
Abstract: Optically resonant donor polymers can exploit a wider range of the solar spectrum effectively without a complicated tandem design in an organic solar cell. Ultrafast Forster resonance energy transfer (FRET) in a polymer-polymer system that significantly improves the power conversion efficiency in bulk heterojunction polymer solar cells from 6.8% to 8.9% is demonstrated, thus paving the way to achieving 15% efficient solar cells.
200 citations
TL;DR: Modification of an ITO electrode with small-molecule organic surface modifier, 4-chloro-benzoic acid (CBA), via a simple spin-coating method produces a high-work-function electrode with high transparency and a hydrophobic surface.
Abstract: Modification of an ITO electrode with small-molecule organic surface modifier, 4-chloro-benzoic acid (CBA), via a simple spin-coating method produces a high-work-function electrode with high transparency and a hydrophobic surface. As an alternative to PEDOT:PSS, CBA modification achieves efficiency enhancement up to 8.5%, which is attributed to enhanced light absorption within the active layer and smooth hole transport from the active layer to the anode.
90 citations
TL;DR: This work demonstrates solution-processed ultrasensitive broad-band photodetectors utilizing organolead halide perovskite materials and PbS quantum dots as light harvesters using diminutive molecular-scaled CH3NH3PbI3 and shows device performance parameters comparable to those from pristine inorganic counterparts.
Abstract: Sensing from ultraviolet-visible to infrared is critical for both scientific and industrial applications. In this work, we demonstrate solution-processed ultrasensitive broad-band photodetectors (PDs) utilizing organolead halide perovskite materials (CH3NH3PbI3) and PbS quantum dots (QDs) as light harvesters. Through passivating the structural defects on the surface of PbS QDs with diminutive molecular-scaled CH3NH3PbI3, both trap states in the bandgap of PbS QDs for charge carrier recombination and the leakage currents occurring at the defect sites are significantly reduced. In addition, CH3NH3PbI3 itself is an excellent light harvester in photovoltaics, which contributes a great photoresponse in the ultraviolet-visible region. Consequently, operated at room temperature, the resultant PDs show a spectral response from 375 nm to 1100 nm, with high responsivities over 300 mA W−1 and 130 mA W−1, high detectivities exceeding 1013 Jones (1 Jones = 1 cm Hz1/2 W−1) and 5 × 1012 Jones in the visible and near infrared regions, respectively. These device performance parameters are comparable to those from pristine inorganic counterparts. Thus, our results offer a facile and promising route for advancing the performance of broad-band PDs.
90 citations
TL;DR: By utilizing a pH neutral, water/alcohol soluble conjugated polyelectrolyte CPE-K as the HTL in p-DTS(PTTh2)2:PC71BM solar cells, a 60% enhancement in PCE has been obtained with an increased V, reduced R, and improved charge extraction.
Abstract: The intrinsic acidic nature of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole-transporting layer (HTL) induces interfacial protonation and limits the device performance in organic solar cells based on basic pyridylthiadiazole units. By utilizing a pH neutral, water/alcohol soluble conjugated polyelectrolyte CPE-K as the HTL in p-DTS(PTTh2)2:PC71BM solar cells, a 60% enhancement in PCE has been obtained with an increased Vbi, reduced Rs, and improved charge extraction. These effects originate from the elimination of interfacial protonation and energy barrier compared with the PEDOT:PSS HTL.
67 citations
TL;DR: In this article, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to study the molecular orientation of blade-coating thin films of regioregular PCDTPT (poly[4,4-dihexadecyl-4H-cyclopenta]dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4]-pyridine]) on substrates with and without uniaxial nanogrooves.
Abstract: The characterization of the microstructure and molecular orientation is critical to understanding the performance of conjugated polymer semiconductors. In this work, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to study the molecular orientation of blade-coating thin films of regioregular PCDTPT (poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine]) on substrates with and without uniaxial nanogrooves. The prediction of NEXAFS spectra through density functional theory calculations allowed for the interpretation of the experimental spectral features and provided information about molecular orientation. Using the polarization dependence of the Nitrogen 1s to π*-resonance signals, the molecular orientation was quantified through calculations of the order parameters S (out-of-plane) and η (in-plane) for both the top side and bottom side of the film. All films have out-of-plane orientation where the conjugated backbones have a pre...
TL;DR: The determination of the band structure along k parallel to the chain direction demonstrates significant electronic delocalization and the small effective mass is consistent with the high measured mobility.
Abstract: The determination of the band structure along k parallel to the chain direction demonstrates significant electronic delocalization. The small effective mass [m* = 0.106mo ] is consistent with the high measured mobility.
TL;DR: The ultrafast charge generation process in organic solar cell devices is investigated by transient reflection spectroscopy on five state-of-the-art bulk heterojunction systems and the lack of electric field dependence in the charge dynamics rules out geminate recombination as an important loss mechanism.
Abstract: The ultrafast charge generation process in organic solar cell devices is investigated by transient reflection spectroscopy on five state-of-the-art bulk heterojunction systems. The charge generation process in operating devices is found to be a combination of an ultrafast generation mechanism over several hundred femto-seconds and a slow process from pico-seconds to nanoseconds, limited by exciton diffusion dynamics. In addition, the lack of electric field dependence in the charge dynamics rules out geminate recombination as an important loss mechanism.
TL;DR: It is demonstrated that two representative fibril-forming proteins, lysozyme and insulin, from the amyloids family can determine the optical signature of rhodamine 6G.
Abstract: Amyloid fibrils are excellent bioderived nanotemplates for controlling molecular and optical properties of small molecules such as organic dyes. Here we demonstrate that two representative fibril-forming proteins, lysozyme and insulin, from the amyloids family can determine the optical signature of rhodamine 6G. Their structural variety leads to a unique molecular arrangement of dye aggregates on the biotemplate surface. This significantly influences the light amplification threshold as well as the stimulated emission profiles, which show remarkable broadband wavelength tunability. We show in addition that amyloid fibrils can be potentially used in constructing broadband emission biolasers.
TL;DR: A novel application of transient photocurrent and short-circuit variable time-delayed collection field measurements is used to reconstruct the complete charge carrier mobility distribution for the photogenerated carriers in optimized organic solar cells.
Abstract: Charge carrier transport through organic solar cells is fundamentally dispersive due to the disordered structure and complex film morphology within the photoactive layer. A novel application of transient photocurrent and short-circuit variable time-delayed collection field measurements is used to reconstruct the complete charge carrier mobility distribution for the photogenerated carriers in optimized organic solar cells.
TL;DR: In this article, the proportion of intermixed domains and pure domains in an amorphous polymer and fullerene BHJ thin film was controlled by varying the fraction of pure polymer domains.
Abstract: Understanding how intermixed domains and pure domains in bulk heterojunction (BHJ) thin films affect charge generation and recombination in polymer solar cells (PSCs) is important to further improve PSC device performance. We control the proportion of intermixed domains and pure domains in an amorphous polymer and fullerene BHJ thin films by varying the fullerene concentration. By studying these thin films with ultrafast spectroscopy, we found that the coherent ultrafast charge generation process is nonexistent in this BHJ system due to the lack of pure polymer domains. We also found that the BHJ thin film with 100% intermixed domains begins charge recombination immediately after the initial charge generation process, while the BHJ thin film with pure fullerene domains showed an additional slow excitonic charge generation process before a slower charge recombination takes place. These results clearly demonstrate that pure domains are important for optimal BHJ solar cell performance.
TL;DR: A tandem solar cell based on a combination of an amorphous silicon (a-Si) and polymer solar cell (PSC) is demonstrated to reduce the cost of electricity produced by photovoltaics.
Abstract: A tandem solar cell based on a combination of an amorphous silicon (a-Si) and polymer solar cell (PSC) is demonstrated. As these tandem devices can be readily fabricated by low-cost methods, they require only a minor increase in the total manufacturing cost. Therefore, a combination of a-Si and PSC provides a compelling solution to reduce the cost of electricity produced by photovoltaics.
TL;DR: In this paper, transient absorption spectroscopy was used to identify torsional modes associated with excited state relaxation and localization in an organic photovoltaic blend and showed that a significant fraction of charge transfer occurs prior to excited state localization.
Abstract: Charge generation in an organic photovoltaic blend was investigated using transient absorption spectroscopy. In films of pure electron donating material, subpicosecond spectral oscillations were observed and assigned to torsional modes associated with excited state relaxation and localization. These modes are systematically suppressed in the presence of fullerene, indicating that a significant fraction of charge transfer occurs prior to excited state localization.
TL;DR: In this paper, four isomorphic organic semiconductors are compared to map out how the precision of chemical structures determines solid state molecular organization and the relative location of the electron accepting fragments within a given molecule.
Abstract: Four isomorphic organic semiconductors are compared to map out how the precision of chemical structures determines solid state molecular organization. Intramolecular electronic structure and intermolecular packing preference in the solid state were shown to be exclusively dependent on the relative location of the electron accepting fragments within a given molecule.
08 Sep 2015
TL;DR: In this paper, a general strategy is presented to self-assemble unidirectional alignment and efficient charge transport for semiconducting polymer films deposited on textured Si/SiO2 substrates.
Abstract: New Science: The field of bulk heterojunction (BHJ) solar cells was created as a result of the discovery of ultrafast charge transfer. The length scale for the wavefunction describing the probability amplitude for finding a photoexcitation at a particular point in space was estimated using position–momentum uncertainty as expressed by the uncertainty principle. The problem can also be considered semi-classically and a very similar estimate of the length scale of the photoexcitation wavefunction is obtained via the resolution limit of a microscope; (λ/2πn) where n is the index of refraction. Finally, the BHJ solar cell should be especially sensitive to the effective interaction volume of the photon because it is comprised of a densely packed collection of strong absorbers. The photoexcitation process, therefore, generates a delocalized coherent superposition of the eigenfunctions of the Schrodinger equation that describes the nanostructured blend, with an immediate probability amplitude for finding a photoexcitation near a BHJ boundary enabling charge transfer in the femtosecond regime over relatively long distances. New Technology: A general strategy is presented to self-assemble unidirectional alignment and efficient charge transport for semiconducting polymer films deposited on textured Si/SiO2 substrates. By employing sandwich casting in a tilted tunnel system, we utilize capillary action, generated by functionalized spacers, to self-assemble semiconducting polymers along uniaxial nano-grooves on the substrate. The strength of capillary action can be tailored by different surface treatments of the glass spacers. PTS functionalization yields highly oriented crystalline films with compact structure with µh = 25.4 cm2 V−1 s−1 and µh = 22.2 cm2 V−1 s−1 for PCDTPT and CDTBTZ, respectively. These values are limited by the S–D contact resistance, Rc. Using longer channels, Rc is significantly less than the channel resistance and µ = 36.3 cm2 V−1 s−1 was measured. Extrapolating to infinite channel length, the intrinsic mobility for PCDTPT is obtained at this degree of chain alignment and structural order: µ = 47 cm2 V−1 s−1. The mobility is strongly anisotropic with 13.6- and 17.6-fold higher values parallel to the direction of polymer alignment.