In this work, we synthesized water-soluble polyfluorene derivatives (WPFs) with anionic and/or cationic side chains, which were used as an indium tin oxide (ITO) cathode interfacial layer in inverted ...polymer solar cells. Three WPFs (WPFN+, WPFZW, and WPFS-) were obtained via Suzuki coupling reactions. Their solubility in polar solvents allowed the WPFs to be used as interfacial layers in inverted polymer solar cells (I-PSCs). Among the WPF-modified ITO electrodes, WPFN+ (with ammonium side chains)-modified ITO can be used as a cathode for electron extraction, while WPFS- (with sulfonate side chains)-modified ITO cannot extract electrons in I-PSCs based on poly(3-hexylthiophene): 6,6-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM). The electron extraction of WPF-modified ITO can mainly be attributed to the different dipole formations at the WPF/ITO interfaces, based on the types of ionic groups on the side chains of the polyfluorene. In addition, we observed that the extent of ITO work-function modification was not always exactly correlated with the device performance based on the results obtained using a WPFZW (with ammonium and sulfonate side chains)-modified ITO electrode.
Fluorine (F) substitution on conjugated polymers in polymer solar cells (PSCs) has a diverse effect on molecular properties and device performance. We present a series of three D-A type conjugated ...polymers (PBT, PFBT, and PDFBT) based on dithienothiophene and benzothiadiazole units with different numbers of F atoms to explain the influence of F substitution by comparing the molecular interactions of the polymers and the recombination kinetics in PSCs. The preaggregation behavior of PFBT and PDFBT in o-DCB at the UV–vis absorption spectra proves that both polymers have strong intermolecular interactions. Besides, more closely packed structures and change into face-on orientation of fluorinated polymers are observed in polymer:PC71BM blends by GIXD which is beneficial for charge transport and, ultimately, for current density in PSCs (4.3, 13.0, and 14.5 mA cm–2 for PBT, PFBT, and PDFBT, respectively). Also, the introduction of F atoms on conjugated backbones affects the recombination kinetics by suppressing bimolecular recombination, thereby improving the fill factor (0.41, 0.68, and 0.69 for PBT, PFBT, and PDFBT, respectively). Consequently, the PCE of PSCs reached 7.3% without any additional treatment (annealing, solvent additive, etc.) in the polymer containing difluorinated BT (PDFBT) that is much higher than nonfluorinated BT (PBT ∼ 1%) and monofluorinated BT (PFBT ∼ 6%).
Abstract
Hybrid structures of silicon with organic–inorganic perovskites are proposed for optically controllable switching of terahertz (THz) waves over a broad spectral range from 0.2 to 2THz. A ...532-nm external laser was utilized to generate photoexcited free carriers at the devices and consequentially to control the terahertz amplitude modulation, obtaining a depth of up to 68% at a laser irradiance of 1.5 W/cm
2
. In addition, we compared the performances from three types of perovskite devices fabricated via different solution processing methods and suggested a stable and highly efficient THz switch based on a one-step processing. By this we demonstrated the possibility of perovskites as THz wave switching devices in addition to photovoltaics.
The work-function of indium tin oxide (ITO) electrodes was tuned with an interfacial dipole layer (WPF-oxy-F) to reverse the polarity in polymer solar cells (PSCs) with an inverted structure. The ...photoactive layer was based on poly(3-hexylthiophene) (P3HT) and 6,6-phenyl-C61-butyric acid methyl ester (PCBM). Silver (Ag) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were used as the top anode. The optimized conditions for the fabricated I-PSCs included an open-circuit voltage (Voc) of 0.68V, a fill factor (FF) of 64%, and a power conversion efficiency (PCE) of 3.86% through post-annealing at 170°C. The high performance of I-PSC is due partly to the improved interfacial contact at active/PEDOT:PSS and mainly to the increase of the work-function of annealed PEDOT:PSS/Ag at 170°C for 30min. Here, we investigated the effect of post-annealing on I-PSC devices by carrying out various annealing sequences.
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•Conjugated polyelectrolyte was used as an electron selective layer in inverted polymer solar cells.•The post-annealed devices at 170°C shows optimized efficiency of 3.86%.•We carried out various annealing sequences to investigate the effect of post-annealing on devices.
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•We investigated the effects of side chain functionality and length on organic memory.•WPFs showed reliable non-volatile characteristics and good device-to-device uniformity.•WPFs ...with the EO side chains showed better memory characteristics than those of the alkyl side chains.•As the EO unit lengthened, the ON/OFF ratio of the memory device gradually increased.•As the EO unit lengthened, the threshold voltages progressively decreased.
This paper investigates the effects of side chains, which are important structural constituents, on the characteristics of organic resistive memory devices with water-soluble polyfluorene (WPF) derivatives. The WPF derivatives have either an ethylene oxide (EO) or an alkyl side chain the lengths of the EO side chains are 2, 4, or 6 molecules. WPFs exhibit typical bipolar switching behaviors with reliable non-volatile characteristics and good device-to-device uniformity under ambient conditions. WPFs with the EO side chains showed better memory characteristics than those of the alkyl side chains of similar length. In addition, as the EO unit lengthened, the ON/OFF ratio of the memory device gradually increased from 5×102 to 105, and the threshold voltage (Vth) progressively decreased from 4 to 3.5V. The retention times for WPF-hexyl, WPF-2O, WPF-4O, and WPF-6O are 104, 200, 104, and 104s, respectively. The excellent switching properties of WPF-4O and WPF-6O are believed to be mainly attributed to highly localized current pathways and the low trap density.
Perovskite solar cells (PeSCs) have been considered one of the competitive next generation power sources. To date, light-to-electric conversion efficiencies have rapidly increased to over 10%, and ...further improvements are expected. However, the poor device reproducibility of PeSCs ascribed to their inhomogeneously covered film morphology has hindered their practical application. Here, we demonstrate high-performance PeSCs with superior reproducibility by introducing small amounts of N-cyclohexyl-2-pyrrolidone (CHP) as a morphology controller into N,N-dimethylformamide (DMF). As a result, highly homogeneous film morphology, similar to that achieved by vacuum-deposition methods, as well as a high PCE of 10% and an extremely small performance deviation within 0.14% were achieved. This study represents a method for realizing efficient and reproducible planar heterojunction (PHJ) PeSCs through morphology control, taking a major step forward in the low-cost and rapid production of PeSCs by solving one of the biggest problems of PHJ perovskite photovoltaic technology through a facile method.
Organometallic halide perovskite-based solar cells have exhibited rapidly increasing efficiencies through the use of mesoporous composites. The addition of materials used in organic solar cells to ...perovskite-based solar cells (PSCs) enables the fabrication of low-cost, flexible, low-temperature, solution-processed PSCs. However, obtaining sufficient coverage of the organic layer, usually poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS), with CH3NH3PbI3–x Cl x films remains difficult in spite of the advances. In this study, we investigated the influence of controlling the solvent evaporation rate on the degree of PEDOT:PSS surface coverage by CH3NH3PbI3–x Cl x . We determined that an adequately fast spinning speed, drying at room temperature, and stepwise ramp annealing are critical for obtaining optimized planar hybrid perovskite solar cells with an ITO/PEDOT:PSS/CH3NH3PbI3–x Cl x /PCBM/Al structure and efficiencies of up to 11.8%.
Hybrid structures of silicon with organic-inorganic perovskites are proposed for optically controllable switching of terahertz (THz) waves over a broad spectral range from 0.2 to 2THz. A 532-nm ...external laser was utilized to generate photoexcited free carriers at the devices and consequentially to control the terahertz amplitude modulation, obtaining a depth of up to 68% at a laser irradiance of 1.5 W/cm
. In addition, we compared the performances from three types of perovskite devices fabricated via different solution processing methods and suggested a stable and highly efficient THz switch based on a one-step processing. By this we demonstrated the possibility of perovskites as THz wave switching devices in addition to photovoltaics.
Despite the significant advantages of liquid metals, such as outstanding mechanical deformability and good electrical conductivity, their intrinsic opacity and unsuitability for conventional ...photolithography processing have limited their extensive utilization for transparent conductive films. Herein, we present the formation of transparent and stretchable electrodes of liquid metals using a direct printing method with high resolutions. Conductive grid structures of liquid metals can be printed directly at room temperature with linewidth below 5 µm with no additional processing, and they exhibit superb optoelectronic properties (low sheet resistance of 1.7 Ω sq−1 at high transmittance of 90.1%). Also, after their encapsulation with an elastomeric layer, these fine grid patterns are transferrable from printed regions onto various nonplanar surfaces. In addition, the bifacial perovskite solar cells fabricated using these transparent electrodes have high power conversion efficiency, i.e., 14.12%, with an outstanding bifaciality factor of 81.09%. In addition, these fine grids of liquid metals can be operated as transparent heaters that operate reliably and have rapid heating rates even in the extremely cold environment of − 30 °C, which is significantly lower than their melting temperature (15.5 °C). Thus, their use may be a promising strategy for next-generation free-form electronics and automobile applications.
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•Liquid metal can be printed high-resolution by using a direct printing.•The printed liquid metals have high conductivity at room temperature without additional processing.•The liquid metal grids are transferrable onto various surfaces of objects after encapsulation with an elastomeric layer.•Liquid metal grid structure also applicable to transparent heaters.
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