Showing papers by "Aram Amassian published in 2017"
TL;DR: This work demonstrates highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device.
Abstract: Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V. Ternary organic blends using two non-fullerene acceptors are shown to improve the efficiency and stability of low-cost solar cells based on P3HT and of high-performance photovoltaic devices based on low-bandgap donor polymers.
887 citations
TL;DR: In this paper, the authors demonstrate cesium cation (Cs+) doped 2D (BA)2(MA)3Pb4I13 perovskite solar cells giving a power conversion efficiency (PCE) as high as 13.7%.
Abstract: Two-dimensional (2D) organic–inorganic perovskites have recently emerged as one of the most important thin-film solar cell materials owing to their excellent environmental stability. The remaining major pitfall is their relatively poor photovoltaic performance in contrast to 3D perovskites. In this work we demonstrate cesium cation (Cs+) doped 2D (BA)2(MA)3Pb4I13 perovskite solar cells giving a power conversion efficiency (PCE) as high as 13.7%, the highest among the reported 2D devices, with excellent humidity resistance. The enhanced efficiency from 12.3% (without Cs+) to 13.7% (with 5% Cs+) is attributed to perfectly controlled crystal orientation, an increased grain size of the 2D planes, superior surface quality, reduced trap-state density, enhanced charge-carrier mobility and charge-transfer kinetics. Surprisingly, it is found that the Cs+ doping yields superior stability for the 2D perovskite solar cells when subjected to a high humidity environment without encapsulation. The device doped using 5% Cs+ degrades only ca. 10% after 1400 hours of exposure in 30% relative humidity (RH), and exhibits significantly improved stability under heating and high moisture environments. Our results provide an important step toward air-stable and fully printable low dimensional perovskites as a next-generation renewable energy source.
568 citations
TL;DR: This work introduces a new method for the synthesis of solution-phase ligand-exchanged CQD inks that enable a flat energy landscape and an advantageously high packing density and demonstrates solar cells with higher Voc and more efficient charge injection into the electron acceptor, allowing the use of a closer-to-optimum bandgap to absorb more light.
Abstract: Bandtail states in disordered semiconductor materials result in losses in open-circuit voltage (Voc) and inhibit carrier transport in photovoltaics. For colloidal quantum dot (CQD) films that promise low-cost, large-area, air-stable photovoltaics, bandtails are determined by CQD synthetic polydispersity and inhomogeneous aggregation during the ligand-exchange process. Here we introduce a new method for the synthesis of solution-phase ligand-exchanged CQD inks that enable a flat energy landscape and an advantageously high packing density. In the solid state, these materials exhibit a sharper bandtail and reduced energy funnelling compared with the previous best CQD thin films for photovoltaics. Consequently, we demonstrate solar cells with higher Voc and more efficient charge injection into the electron acceptor, allowing the use of a closer-to-optimum bandgap to absorb more light. These enable the fabrication of CQD solar cells made via a solution-phase ligand exchange, with a certified power conversion efficiency of 11.28%. The devices are stable when stored in air, unencapsulated, for over 1,000 h.
525 citations
TL;DR: The one-step spin-coating process of perovskites is investigated in situ, revealing that thin-film formation is mediated by solid-state precursor solvates and their nature.
Abstract: Solution-processed hybrid perovskite semiconductors attract a great deal of attention, but little is known about their formation process. The one-step spin-coating process of perovskites is investigated in situ, revealing that thin-film formation is mediated by solid-state precursor solvates and their nature. The stability of these intermediate phases directly impacts the quality and reproducibility of thermally converted perovskite films and their photovoltaic performance.
148 citations
TL;DR: In this Review, insights into the fundamentals of solution-based film deposition afforded by recent state-of-the-art in situ measurements of functional film drying are highlighted and emphasis is placed on multimodal studies that combine surface-sensitive X-ray scattering with optical characterization to clearly define the evolution of solute structure with film thickness.
Abstract: Solution-processed organic films are a facile route to high-speed, low cost, large-area deposition of electrically functional components (transistors, solar cells, emitters, etc.) that can enable a diversity of emerging technologies, from Industry 4.0, to the Internet of things, to point-of-use heath care and elder care. The extreme sensitivity of the functional performance of organic films to structure and the general nonequilibrium nature of solution drying result in extreme processing–performance correlations. In this Review, we highlight insights into the fundamentals of solution-based film deposition afforded by recent state-of-the-art in situ measurements of functional film drying. Emphasis is placed on multimodal studies that combine surface-sensitive X-ray scattering (GIWAXS or GISAXS) with optical characterization to clearly define the evolution of solute structure (aggregation, crystallinity, and morphology) with film thickness.
145 citations
TL;DR: In this paper, the electrical conductivity of conjugated poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7, 8,8,8-tetracyanoquinodimethane (F4TCNQ) was investigated.
Abstract: Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) is a widely studied model system. Underlying structure-property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm-1 for P3HT:F4TCNQ. We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10-4 mol cm-3 is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10-1 cm2 V-1 s-1. Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure-property relationships of strongly doped conjugated polymers.
130 citations
TL;DR: It is found that In 2O3/ZnO transistors exhibit band-like electron transport, with mobility values significantly higher than single-layer In2O3 and ZnO devices by a factor of 2 to 100, demonstrating engineering of solution-grown metal oxide heterointerfaces as an alternative strategy to thin-film transistor development and has the potential for widespread technological applications.
Abstract: Thin-film transistors made of solution-processed metal oxide semiconductors hold great promise for application in the emerging sector of large-area electronics. However, further advancement of the technology is hindered by limitations associated with the extrinsic electron transport properties of the often defect-prone oxides. We overcome this limitation by replacing the single-layer semiconductor channel with a low-dimensional, solution-grown In2O3/ZnO heterojunction. We find that In2O3/ZnO transistors exhibit band-like electron transport, with mobility values significantly higher than single-layer In2O3 and ZnO devices by a factor of 2 to 100. This marked improvement is shown to originate from the presence of free electrons confined on the plane of the atomically sharp heterointerface induced by the large conduction band offset between In2O3 and ZnO. Our finding underscores engineering of solution-grown metal oxide heterointerfaces as an alternative strategy to thin-film transistor development and has the potential for widespread technological applications.
128 citations
TL;DR: Ultraviolet photoelectron spectroscopy measurements on the glass/indium-tin oxide/SnO2/methylammonium lead iodide/2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene device stack indicate that extraction of photogenerated electrons is facilitated by a perfect alignment of the conduction bands at the SnO2
Abstract: Chemical bath deposition (CBD) of tin oxide (SnO2) thin films as an electron-transport layer (ETL) in a planar-heterojunction n–i–p organohalide lead perovskite and organic bulk-heterojunction (BHJ) solar cells is reported. The amorphous SnO2 (a-SnO2) films are grown from a nontoxic aqueous bath of tin chloride at a very low temperature (55 °C) and do not require postannealing treatment to work very effectively as an ETL in a planar-heterojunction n–i–p organohalide lead perovskite or organic BHJ solar cells, in lieu of the commonly used ETL materials titanium oxide (TiO2) and zinc oxide (ZnO), respectively. Ultraviolet photoelectron spectroscopy measurements on the glass/indium–tin oxide (ITO)/SnO2/methylammonium lead iodide (MAPbI3)/2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene device stack indicate that extraction of photogenerated electrons is facilitated by a perfect alignment of the conduction bands at the SnO2/MAPbI3 interface, while the deep valence band of SnO2 ensures stro...
125 citations
TL;DR: In this article, a low-bandgap donor polymer (PffBT4T-2DT) and a non-fullerene acceptor (EH-IDTBR) was used as the solvent, rather than chlorobenzene, to improve power conversion efficiency.
Abstract: With chlorinated solvents unlikely to be permitted for use in solution-processed organic solar cells in industry, there must be a focus on developing nonchlorinated solvent systems Here we report high-efficiency devices utilizing a low-bandgap donor polymer (PffBT4T-2DT) and a nonfullerene acceptor (EH-IDTBR) from hydrocarbon solvents and without using additives When mesitylene was used as the solvent, rather than chlorobenzene, an improved power conversion efficiency (111%) was achieved without the need for pre- or post-treatments Despite altering the processing conditions to environmentally friendly solvents and room-temperature coating, grazing incident X-ray measurements confirmed that active layers processed from hydrocarbon solvents retained the robust nanomorphology obtained with hot-processed chlorinated solvents The main advantages of hydrocarbon solvent-processed devices, besides the improved efficiencies, were the reproducibility and storage lifetime of devices Mesitylene devices showed b
88 citations
TL;DR: In this paper, the authors acknowledge the project Progetto di ricerca PON MAAT (Project Number: PON02_00563_3316357) and PERSEO-PERovskite-based solar cells: towards high efficiency and long-term stability.
Abstract: S.C. and A.L. acknowledge Regione Puglia and ARTI for funding FIR—future in research projects “PeroFlex” project no. LSBC6N4 and “HyLight” project no. GOWMB21. The authors acknowledge the project Progetto di ricerca PON MAAT (Project Number: PON02_00563_3316357) and PERSEO-“PERovskite-based solar cells: towards high efficiency and long-term stability” (Bando PRIN 2015-Italian Ministry of University and Scientific Research (MIUR) Decreto Direttoriale 4 novembre 2015 n. 2488, project number 20155LECAJ) for funding. A.R. and S.M. gratefully acknowledge SIR project “Two-Dimensional Colloidal Metal Dichalcogenides based Energy-Conversion Photovoltaics” (2D ECO), Bando SIR (Scientific Independence of young Researchers) 2014 MIUR Decreto Direttoriale 23 gennaio 2014 no. 197 (project number RBSI14FYVD, CUP: B82I15000950008) for funding. The authors acknowledge Sonia Carallo for technical support. N.D.T. acknowledges support from the National Science Foundation's International Research Fellowship Program (OISE-1201915) and the European Research Council's Marie Curie International Incoming Fellowship under grant agreement number 300091. N.S. is by a European Research Council Starting Independent Researcher Fellowship under grant agreement number 279587. We thank Dr. Detlef-M. Smilgies from the Cornell High Energy Synchrotron Source (CHESS) for his assistance with in situ GIWAXS measurements. CHESS is supported by the NSF & NIH/NIGMS via NSF award DMR-1332208. A.A. and R.M. are thankful for the support of the King Abdullah University of Science and Technology (KAUST) and the KAUST Solar Center.
77 citations
TL;DR: In this paper, a set of widebandgap polymer donor analogues composed of benzo[1,2-b:4,5-b′]dithiophene (BDT), and thienyl ([2H]T] or 3,4-difluorothiophene ([2F]T) motifs were examined and correlated with BHJ device performance patterns.
Abstract: “Nonfullerene” acceptors are proving effective in bulk heterojunction (BHJ) solar cells when paired with selected polymer donors. However, the principles that guide the selection of adequate polymer donors for high-efficiency BHJ solar cells with nonfullerene acceptors remain a matter of some debate and, while polymer main-chain substitutions may have a direct influence on the donor–acceptor interplay, those effects should be examined and correlated with BHJ device performance patterns. This report examines a set of wide-bandgap polymer donor analogues composed of benzo[1,2-b:4,5-b′]dithiophene (BDT), and thienyl ([2H]T) or 3,4-difluorothiophene ([2F]T) motifs, and their BHJ device performance pattern with the nonfullerene acceptor “ITIC”. Studies show that the fluorine- and ring-substituted derivative PBDT(T)[2F]T largely outperforms its other two polymer donor counterparts, reaching power conversion efficiencies as high as 9.8%. Combining several characterization techniques, the gradual device performance improvements observed on swapping PBDT[2H]T for PBDT[2F]T, and then for PBDT(T)[2F]T, are found to result from (i) notably improved charge generation and collection efficiencies (estimated as ≈60%, 80%, and 90%, respectively), and (ii) reduced geminate recombination (being suppressed from ≈30%, 25% to 10%) and bimolecular recombination (inferred from recombination rate constant comparisons). These examinations will have broader implications for further studies on the optimization of BHJ solar cell efficiencies with polymer donors and a wider range of nonfullerene acceptors.
TL;DR: Poly(ethylene oxide) is demonstrated to be a suitable matrix polymer for the solution‐doped conjugated polymer poly(3‐hexylthiophene) and free‐standing, mechanically robust tapes illustrate the versatility of the developed dopant:semiconductor:insulator ternary blends.
Abstract: Poly(ethylene oxide) is demonstrated to be a suitable matrix polymer for the solution-doped conjugated polymer poly(3-hexylthiophene). The polarity of the insulator combined with carefully chosen processing conditions permits the fabrication of tens of micrometer-thick films that feature a fine distribution of the F4TCNQ dopant:semiconductor complex. Changes in electrical conductivity from 0.1 to 0.3 S cm−1 and Seebeck coefficient from 100 to 60 μV K−1 upon addition of the insulator correlate with an increase in doping efficiency from 20% to 40% for heavily doped ternary blends. An invariant bulk thermal conductivity of about 0.3 W m−1 K−1 gives rise to a thermoelectric Figure of merit ZT ∼ 10−4 that remains unaltered for an insulator content of more than 60 wt%. Free-standing, mechanically robust tapes illustrate the versatility of the developed dopant:semiconductor:insulator ternary blends.
TL;DR: Experimental results suggest that the inhomogeneous strain induced in organic semiconductor layers by the mismatch between the coefficients of thermal expansion (CTE) of the consecutive device layers of field-effect transistors generates trapping states that localize charge carriers.
Abstract: The temperature dependence of the charge-carrier mobility provides essential insight into the charge transport mechanisms in organic semiconductors. Such knowledge imparts critical understanding of the electrical properties of these materials, leading to better design of high-performance materials for consumer applications. Here, we present experimental results that suggest that the inhomogeneous strain induced in organic semiconductor layers by the mismatch between the coefficients of thermal expansion (CTE) of the consecutive device layers of field-effect transistors generates trapping states that localize charge carriers. We observe a universal scaling between the activation energy of the transistors and the interfacial thermal expansion mismatch, in which band-like transport is observed for similar CTEs, and activated transport otherwise. Our results provide evidence that a high-quality semiconductor layer is necessary, but not sufficient, to obtain efficient charge-carrier transport in devices, and underline the importance of holistic device design to achieve the intrinsic performance limits of a given organic semiconductor. We go on to show that insertion of an ultrathin CTE buffer layer mitigates this problem and can help achieve band-like transport on a wide range of substrate platforms.
TL;DR: These findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surface passivation strategies to remediate them.
Abstract: Understanding defect chemistry, particularly ion migration, and its significant effect on the surface’s optical and electronic properties is one of the major challenges impeding the development of hybrid perovskite-based devices. Here, using both experimental and theoretical approaches, we demonstrated that the surface layers of the perovskite crystals may acquire a high concentration of positively charged vacancies with the complementary negatively charged halide ions pushed to the surface. This charge separation near the surface generates an electric field that can induce an increase of optical band gap in the surface layers relative to the bulk. We found that the charge separation, electric field, and the amplitude of shift in the bandgap strongly depend on the halides and organic moieties of perovskite crystals. Our findings reveal the peculiarity of surface effects that are currently limiting the applications of perovskite crystals and more importantly explain their origins, thus enabling viable surf...
TL;DR: The results revealed that both thermal cycling and high temperatures produce irreversible detrimental effects on the PSC performance because of the deteriorated interfacial photocarrier extraction, suggesting that the development of robust charge transporters and proper interface engineering are critical for the deployment of perovskite PVs in harsh thermal environments.
Abstract: In this work, we investigated the effects of high operating temperature and thermal cycling on the photovoltaic (PV) performance of perovskite solar cells (PSCs) with a typical mesostructured (m)-TiO2–CH3NH3PbI3–xClx–spiro-OMeTAD architecture. After temperature-dependent grazing-incidence wide-angle X-ray scattering, in situ X-ray diffraction, and optical absorption experiments were carried out, the thermal durability of PSCs was tested by subjecting the devices to repetitive heating to 70 °C and cooling to room temperature (20 °C). An unexpected regenerative effect was observed after the first thermal cycle; the average power conversion efficiency (PCE) increased by approximately 10% in reference to the as-prepared device. This increase of PCE was attributed to the heating-induced improvement of the crystallinity and p doping in the hole transporter, spiro-OMeTAD, which promotes the efficient extraction of photogenerated carriers. However, further thermal cycles produced a detrimental effect on the PV pe...
TL;DR: In this paper, a modified two-step interdiffusion protocol was proposed to produce pinhole-free perovskite solar cells with greatly improved morphology by adding small amounts of glycol ethers.
Abstract: Planar perovskite solar cells can be prepared without high-temperature processing steps typically associated with mesoporous device architectures; however, their efficiency has been lower, and producing high-quality perovskite films in planar devices has been challenging. Here, we report a modified two-step interdiffusion protocol suitable to preparing pinhole-free perovskite films with greatly improved morphology. This is achieved by simple addition of small amounts of glycol ethers to the preparation protocol. We unravel the impact the glycol ethers have on the perovskite film formation using in situ ultraviolet–visible absorbance and grazing incidence wide-angle X-ray scattering experiments. From these experiments we conclude that addition of glycol ethers changes the lead iodide to perovskite conversion dynamics and enhances the conversion efficiency, resulting in more compact polycrystalline films, and it creates micrometer-sized perovskite crystals vertically aligned across the photoactive layer. Co...
TL;DR: In this article, highly dispersible SnO2 nanoparticles were synthesized by a microwave-assisted non-aqueous sol-gel route in an organic medium, which allowed high reproducibility and scalability of the film deposition process.
Abstract: Tin oxide has been demonstrated to possess outstanding optoelectronic properties such as optical transparency and high electron mobility; therefore, it was successfully utilized as an electron transporting layer in various kinds of solar cells. In this study, for the first time, highly dispersible SnO2 nanoparticles were synthesized by a microwave-assisted non-aqueous sol–gel route in an organic medium. Ethanol dispersion of the as-prepared nanoparticles was used to cast a uniform thin layer of SnO2 without the aid of an aggregating agent and at low temperatures. Organohalide perovskite solar cells were fabricated using SnO2 as the electron transporting layer. Morphological and spectroscopic investigations, in addition to the good photoconversion efficiency obtained, evidenced that the nanoparticles synthesized by this route have optimal properties such as small size and crystallinity to form a continuous film. Furthermore, this method allows high reproducibility and scalability of the film deposition process.
TL;DR: This work presents a universal approach that can program the microstructure of materials through the coherent seeding of otherwise stochastic homogeneous nucleation events and is used to demonstrate printed arrays of organic thin-film transistors with remarkable performance and reproducibility owing to their demonstrated spatial control over the microStructure of organic and inorganic polycrystalline semiconductors.
Abstract: The functional properties and technological utility of polycrystalline materials are largely determined by the structure, geometry, and spatial distribution of their multitude of crystals. However, crystallization is seeded through stochastic and incoherent nucleation events, limiting the ability to control or pattern the microstructure, texture, and functional properties of polycrystalline materials. We present a universal approach that can program the microstructure of materials through the coherent seeding of otherwise stochastic homogeneous nucleation events. The method relies on creating topographic variations to seed nucleation and growth at designated locations while delaying nucleation elsewhere. Each seed can thus produce a coherent growth front of crystallization with a geometry designated by the shape and arrangement of seeds. Periodic and aperiodic crystalline arrays of functional materials, such as semiconductors, can thus be created on demand and with unprecedented sophistication and ease by patterning the location and shape of the seeds. This approach is used to demonstrate printed arrays of organic thin-film transistors with remarkable performance and reproducibility owing to their demonstrated spatial control over the microstructure of organic and inorganic polycrystalline semiconductors.
TL;DR: In this paper, a generalized approach to balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells is presented.
Abstract: Employment of thin perovskite shells and metal halides as surface-passivants for colloidal quantum dots (CQDs) has been an important, recent development in CQD optoelectronics. These have opened the route to single-step-deposited high-performing CQD solar cells. These promising architectures employ a CQD hole-transporting layer (HTL) whose intrinsically shallow Fermi level (EF) restricts band-bending at maximum power-point during solar cell operation limiting charge collection. Here, we demonstrate a generalized approach to effectively balance band-edge energy levels of the main CQD absorber and charge-transport layer for these high-performance solar cells. Briefly soaking the CQD HTL in a solution of the metal–organic p-dopant, molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene), effectively deepens its Fermi level, resulting in enhanced band bending at the HTL:absorber junction. This blocks the back-flow of photogenerated electrons, leading to enhanced photocurrent and fill fac...
TL;DR: In this article, the authors combine experimental measurements of vacuum-deposited Rubrene/C60 bilayer OSCs, with varying microstructure and texture, with density functional theory calculations to determine how relative molecular orientations and extents of structural order influence E CT and V OC.
Abstract: In organic solar cells (OSCs), the energy of the charge-transfer (CT) complexes at the donor–acceptor interface, E CT, determines the maximum open-circuit voltage (V OC). The coexistence of phases with different degrees of order in the donor or the acceptor, as in blends of semi-crystalline donors and fullerenes in bulk heterojunction layers, influences the distribution of CT states and the V OC enormously. Yet, the question of how structural heterogeneities alter CT states and the V OC is seldom addressed systematically. In this work, we combine experimental measurements of vacuum-deposited rubrene/C60 bilayer OSCs, with varying microstructure and texture, with density functional theory calculations to determine how relative molecular orientations and extents of structural order influence E CT and V OC. We find that varying the microstructure of rubrene gives rise to CT bands with varying energies. The CT band that originates from crystalline rubrene lies up to ≈0.4 eV lower in energy compared to the one that arises from amorphous rubrene. These low-lying CT states contribute strongly to V OC losses and result mainly from hole delocalization in aggregated rubrene. This work points to the importance of realizing interfacial structural control that prevents the formation of low E CT configurations and maximizes V OC.
TL;DR: In this paper, the fundamental Research Funds for the Central Universities (GK201603055 and GK01010), the Innovation Funds of Graduate Programs, SNNU (2015CXS047), the National University Research Fund (Gk261001009 and Gk201603107), the Changjiang Scholar and Innovative Research Team (IRT_14R33), the 111 Project (B14041), National Key Research Program of China (2016YFA0202403), and the Chinese National 1000-talent-plan program (1110010341
Abstract: J.L. and Y.L. contributed equally to this work. This work was supported by the fundamental Research Funds for the Central Universities (GK201603055 and GK01010), the Innovation Funds of Graduate Programs, SNNU (2015CXS047), the National University Research Fund (GK261001009 and GK201603107), the Changjiang Scholar and Innovative Research Team (IRT_14R33), the 111 Project (B14041), the National Key Research Program of China (2016YFA0202403), and the Chinese National 1000-talent-plan program (1110010341).
TL;DR: In this paper, the authors investigate the solidification of PbI2 films from a DMF solution by performing in situ grazing incidence wide angle X-ray scattering (GIWAXS) measurements.
Abstract: The successful and widely used two-step process of producing the hybrid organic-inorganic perovskite CH3NH3PbI3, consists of converting a solution deposited PbI2 film by reacting it with CH3NH3I. Here, we investigate the solidification of PbI2 films from a DMF solution by performing in situ grazing incidence wide angle X-ray scattering (GIWAXS) measurements. The measurements reveal an elaborate sol–gel process involving three PbI2⋅DMF solvate complexes—including disordered and ordered ones—prior to PbI2 formation. The ordered solvates appear to be metastable as they transform into the PbI2 phase in air within minutes without annealing. Morphological analysis of air-dried and annealed films reveals that the air-dried PbI2 is substantially more porous when the coating process produces one of the intermediate solvates, making this more suitable for subsequent conversion into the perovskite phase. The observation of metastable solvates on the pathway to PbI2 formation open up new opportunities for influencing the two-step conversion of metal halides into efficient light harvesting or emitting perovskite semiconductors.
TL;DR: In this paper, a solution-based, non-covalent surface doping of few-layer graphene (FLG) using a series of molecular metal-organic and organic species of varying n-and p-type doping strengths was demonstrated.
Abstract: Doping of graphene is a viable route toward enhancing its electrical conductivity and modulating its work function for a wide range of technological applications. In this work, the authors demonstrate facile, solution-based, noncovalent surface doping of few-layer graphene (FLG) using a series of molecular metal-organic and organic species of varying n- and p-type doping strengths. In doing so, the authors tune the electronic, optical, and transport properties of FLG. The authors modulate the work function of graphene over a range of 2.4 eV (from 2.9 to 5.3 eV)—unprecedented for solution-based doping—via surface electron transfer. A substantial improvement of the conductivity of FLG is attributed to increasing carrier density, slightly offset by a minor reduction of mobility via Coulomb scattering. The mobility of single layer graphene has been reported to decrease significantly more via similar surface doping than FLG, which has the ability to screen buried layers. The dopant dosage influences the properties of FLG and reveals an optimal window of dopant coverage for the best transport properties, wherein dopant molecules aggregate into small and isolated clusters on the surface of FLG. This study shows how soluble molecular dopants can easily and effectively tune the work function and improve the optoelectronic properties of graphene.
TL;DR: This work demonstrates hybrid tandem cells with a low bandgap PbS CQD subcell harvesting the visible and near-infrared photons and a polymer:fullerene-poly (diketopyrrolopyrrole-terthiophene) (PDPP3T):[6,6]-phenyl-C60-butyric acid methyl ester (PC61BM)-top cell absorbing effectively the red andNear infrared photons of the solar spectrum in a complementary
Abstract: This work was supported by the King Abdullah University of Science and Technology (KAUST) Part of this work was supported by the Competitive Research Grant (round 2, KAUST) and by the KAUST Solar Center's Competitive Research Fund (Project C3) EHS acknowledges funding from the Ontario Research Fund
TL;DR: In this article, the Stille coupling between 4-(4,4-bis(2-ethylhexyl)-6-(trimethylstannyl)-4H-silolo[3,2-b:4,5-b′]dithiophen-2-yl)-7-(5′-hexyl]-2,2′-bithiophens]-5-yl)
Abstract: Two intermediate-sized donor molecules, BBTz-X and BDT-X, have been synthesized by the Stille coupling between 4-(4,4-bis(2-ethylhexyl)-6-(trimethylstannyl)-4H-silolo[3,2-b:4,5-b′]dithiophen-2-yl)-7-(5′-hexyl-[2,2′-bithiophen]-5-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine and either 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-2,6-diiodobenzo[1,2-d:4,5-d′]bis(thiazole) or 2,6-dibromo-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene, respectively. Both oxidation and reduction potentials for BBTz-X are anodically shifted relative to those for BDT-X, but the oxidation potential is more sensitive to the identity of the core; this is consistent with what is seen for DFT-calculated HOMO and LUMO energies and with a slightly blue-shifted absorption maximum for BBTz-X. Although DFT calculations, along with crystal structures of related compounds, suggest more planar molecular structures for BBTz-X than for BDT-X, film structures and the effects of various annealing processes on these films, as revealed by...
TL;DR: In this paper, the first ever organic thin-film transistor fabricated with an electrophotographic laser printing process using a standard office laser printer is reported, making this a successful first demonstration of the potential of laser printing of organic semiconductors.
Abstract: Solution deposition of organic optoelectronic materials enables fast roll-to-roll manufacturing of photonic and electronic devices on any type of substrate and at low cost. But controlling the film microstructure when it crystallizes from solution can be challenging. This represents a major limitation of this technology, since the microstructure, in turn, governs the charge transport properties of the material. Further, the solvents typically used are hazardous, which precludes their incorporation in large-scale manufacturing processes. Here, the first ever organic thin-film transistor fabricated with an electrophotographic laser printing process using a standard office laser printer is reported. This completely solvent-free additive manufacturing method allows for simultaneous deposition, purification, and patterning of the organic semiconductor layer. Laser-printed transistors using triisopropylsilylethynyl pentacene as the semiconductor layer are realized on flexible substrates and characterized, making this a successful first demonstration of the potential of laser printing of organic semiconductors.
TL;DR: This work shows that few-layer graphene (FLG) can be doped using a hybrid approach, effectively combining surface doping by larger (metal-)organic molecules and intercalation of smaller molecules, such as Br2 and FeCl3, into the bulk.
Abstract: Surface molecular doping of graphene has been shown to modify its work function and increase its conductivity. However, the associated shifts in work function and increases in carrier concentration are highly coupled and limited by the surface coverage of dopant molecules on graphene. Here we show that few-layer graphene (FLG) can be doped using a hybrid approach, effectively combining surface doping by larger (metal−)organic molecules and intercalation of smaller molecules, such as Br2 and FeCl3, into the bulk. Intercalation tunes the carrier concentration more effectively, whereas surface doping of intercalated FLG can be used to tune its work function without reducing the carrier mobility. This multimodal doping approach yields a very high carrier density and tunable increase in the work function for FLG, demonstrating a new versatile platform for fabricating graphene-based contacts for electronic, optoelectronic, and photovoltaic applications.
TL;DR: In this paper, the best way to survive is to quickly exit a submersed vehicle and this number increases to 2,000-5,000 in all industrialized nations. But this number may not account for the number of deaths in sub-mersed vehicles.
Abstract: Objective: Every year about 400 people die in submersed vehicles in North America and this number increases to 2,000–5,000 in all industrialized nations. The best way to survive is to quickly exit ...
Patent•
05 Sep 2017
TL;DR: In this paper, a method of fabricating a semiconducting material, comprising fixing a first substrate to a second substrate via a bonding material sufficient to form a two-substrate support with a cavity region, was described.
Abstract: Embodiments of the present disclosure describe a method of fabricating a semiconducting material, comprising fixing a first substrate to a second substrate via a bonding material sufficient to form a two-substrate support with a cavity region, applying an organo-lead halide perovskite precursor solution to the cavity region of the two-substrate support, and annealing sufficient to form in the cavity region a semiconducting material including an organo-lead halide perovskite thin single crystal. Embodiments of the present disclosure further describe a transistor comprising a source terminal, a drain terminal, a channel layer extending between the source terminal and the drain terminal and including an organo-lead halide perovskite thin single crystal, a gate terminal, and an insulating layer separating the gate terminal from the source terminal, drain terminal, and channel layer sufficient to form a transistor.