Showing papers by "Alex K.-Y. Jen published in 2017"
TL;DR: In this article, the introduction of phenylethylammonium iodide (PEAI) into FAPbI3 perovksite to form mixed cation FAxPEA1-xPbI-3 can effectively enhance both phase and ambient stability of the derived devices.
Abstract: In this work, different from the commonly explored strategy of incorporating a smaller cation, MA+ and Cs+ into FAPbI3 lattice to improve efficiency and stability, it is revealed that the introduction of phenylethylammonium iodide (PEAI) into FAPbI3 perovksite to form mixed cation FAxPEA1–xPbI3 can effectively enhance both phase and ambient stability of FAPbI3 as well as the resulting performance of the derived devices. From our experimental and theoretical calculation results, it is proposed that the larger PEA cation is capable of assembling on both the lattice surface and grain boundaries to form quais-3D perovskite structures. The surrounding of PEA+ ions at the crystal grain boundaries not only can serve as molecular locks to tighten FAPbI3 domains but also passivate the surface defects to improve both phase and moisture stablity. Consequently, a high-performance (PCE:17.7%) and ambient stable FAPbI3 solar cell could be developed.
292 citations
TL;DR: P-type inorganic semiconductor CuGaO2 as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) provides higher carrier mobility, better-energy level matching, and superior stability, as well as low-temperature processing technique.
Abstract: The p-type inorganic semiconductor CuGaO2 as a hole-transporting layer (HTL) in perovskite solar cells (PSCs) provides higher carrier mobility, better-energy level matching, and superior stability, as well as low-temperature processing technique. Compared to organic HTL, a very competitive PCE of 18.51% with long-term stability is achieved. This indicates that CuGaO2 is a promising HTL for efficient and stable PSCs.
290 citations
TL;DR: The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskites-pervskite tandems for solar-energy generation and unlocks opportunities for solar water splitting using hybrid perovSKites with solar-to-hydrogen efficiencies beyond 15%.
Abstract: Organic-inorganic hybrid perovskite multijunction solar cells have immense potential to realize power conversion efficiencies (PCEs) beyond the Shockley-Queisser limit of single-junction solar cells; however, they are limited by large nonideal photovoltage loss (V oc,loss ) in small- and large-bandgap subcells. Here, an integrated approach is utilized to improve the V oc of subcells with optimized bandgaps and fabricate perovskite-perovskite tandem solar cells with small V oc,loss . A fullerene variant, Indene-C60 bis-adduct, is used to achieve optimized interfacial contact in a small-bandgap (≈1.2 eV) subcell, which facilitates higher quasi-Fermi level splitting, reduces nonradiative recombination, alleviates hysteresis instabilities, and improves V oc to 0.84 V. Compositional engineering of large-bandgap (≈1.8 eV) perovskite is employed to realize a subcell with a transparent top electrode and photostabilized V oc of 1.22 V. The resultant monolithic perovskite-perovskite tandem solar cell shows a high V oc of 1.98 V (approaching 80% of the theoretical limit) and a stabilized PCE of 18.5%. The significantly minimized nonideal V oc,loss is better than state-of-the-art silicon-perovskite tandem solar cells, which highlights the prospects of using perovskite-perovskite tandems for solar-energy generation. It also unlocks opportunities for solar water splitting using hybrid perovskites with solar-to-hydrogen efficiencies beyond 15%.
259 citations
TL;DR: The power-conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased rapidly from about 4% to 22% during the past few years as mentioned in this paper.
210 citations
TL;DR: In this paper, an ultralow lasing threshold (0.39 μJ/cm2) was obtained for a hybrid vertical cavity surface emitting laser (VCSEL) structure consisting of a CsPbBr3 QD thin film and two highly reflective distributed Bragg reflectors (DBRs).
Abstract: All-inorganic cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) have recently emerged as highly promising solution-processed materials for next-generation light-emitting applications. They combine the advantages of QD and perovskite materials, which makes them an attractive platform for achieving high optical gain with high stability. Here, we report an ultralow lasing threshold (0.39 μJ/cm2) from a hybrid vertical cavity surface emitting laser (VCSEL) structure consisting of a CsPbBr3 QD thin film and two highly reflective distributed Bragg reflectors (DBRs). Temperature dependence of the lasing threshold and long-term stability of the device were also characterized. Notably, the CsPbBr3 QDs provide superior stability and enable stable device operation over 5 h/1.8 × 107 optical pulse excitations under ambient conditions. This work demonstrates the significant potential of CsPbBr3 perovskite QD VCSELs for highly reliable lasers, capable of operating in the short-pulse (femtosecond) and quasi-co...
209 citations
TL;DR: A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs) that show high efficiency and no hysteresis on rigid and flexible substrates, respectively.
Abstract: A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g-1 .
182 citations
TL;DR: In this article, two hole extraction materials (HEMs), namely TPP-OMeTAD and TPP-SMeTAD, have been developed to facilitate the fabrication of efficient p-i-n perovskite solar cells (PVSCs).
Abstract: Two hole-extraction materials (HEMs), TPP-OMeTAD and TPP-SMeTAD, have been developed to facilitate the fabrication of efficient p-i-n perovskite solar cells (PVSCs). By replacing the oxygen atom on HEM with sulfur (from TPP-OMeTAD to TPP-SMeTAD), it effectively lowers the highest occupied molecular orbital of the molecule and provides stronger Pb-S interaction with perovskites, leading to efficient charge extraction and surface traps passivation. The TPP-SMeTAD-based PVSCs exhibit both improved photovoltaic performance and reduced hysteresis in p-i-n PVSCs over those based on TPP-OMeTAD. This work not only provides new insights on creating perovskite-HEM heterojunction but also helps in designing new HEM to enable efficient organic–inorganic hybrid PVSCs.
180 citations
TL;DR: In this article, a fused-ring thiophene-thieno[3,2-b]-based low-band gap electron acceptor, 4TIC, has been designed and synthesized for non-fullerene solar cells.
Abstract: A fused-ring thiophene-thieno[3,2-b]thiophene-thiophene (4T)-based low-band gap electron acceptor, 4TIC, has been designed and synthesized for non-fullerene solar cells. The utilization of the 4T center core enhances the charge mobility of 4TIC and extends its absorption band edge to ∼900 nm, which facilitates its function as a very efficient low-band gap electron acceptor. The rigid, π-conjugated framework of 4T also offers a lower reorganization energy to facilitate lower VOC energy loss. Femtosecond transient spectroscopy showed a level of polaron generation in 4TIC results in the more efficient transfer of energetic carriers higher than that seen with the benchmarked molecule, ITIC. Film morphology analysis has also shown that 4TIC has structural order that is more prominent than that of ITIC with a multiscale phase separation in the blend with donor polymer PTB7-Th. As a result, solar cells based on PTB7-Th and 4TIC exhibit a high power conversion efficiency of 10.43% and a relatively low non-ideal p...
172 citations
TL;DR: A new porphyrin is synthesized and blended with [6,6]-phenyl-C61-butyric acid methyl ester to function as an efficient BHJ for OPV/perovskite hybrid solar cells that afford a very high power conversion efficiency (PCE) (19.02%) with high Voc, JSC, and FF achieved simultaneously.
Abstract: Employing a layer of bulk-heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite-based solar cells, instead of using tandem devices or near infrared (NIR)-absorbing Sn-containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short-circuit current (JSC) and fill factor (FF). To find an appropriate NIR-absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase JSC, but also possess suitable energy levels and high mobility to afford high VOC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well-matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high Voc, JSC, and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.
166 citations
TL;DR: A series of benzoic acid selfassembled monolayers (SAMs) are used to passivate the surface defects of the NiOx NPs and found that 4-bromobenzoic Acid could effectively play the role of the surface passivation, resulting in more stable PSCs with enhanced power conversion efficiency (PCE) of 18.4 %, exceeding the control device PCE (15.5 %).
Abstract: Entirely low-temperature solution-processed (≤ 100 °C) planar p-i-n perovskite solar cells (PVSCs) offer great potential for commercialization of roll-to-roll fabricated photovoltaic devices. However, the stable inorganic hole transporting layer (HTL) in PVSCs is usually processed at high temperature (200 °C ~500 °C) which is far beyond the tolerant temperature (≤ 150 °C) of roll-to-roll fabrication. In this context, inorganic NiOx -nanoparticles (NPs) are an excellent candidate to serve as the HTL in PVSCs, owing to their excellent solution-processability at room temperature. However, the low-temperature processing condition is usually accompanied with defect formation.To suppress this setback, we used a series of benzoic acid self-assembly monolayers (SAMs) to passivate the surface defects of the NiOx NPs, and found that 4-bromobenzoic acid could effectively play the role of the surface passivation. This SAM layer reduces the trap-assisted recombination, minimizes the energy offset between the NiOx NPs and perovskite, and changes the HTL surface wettability, thus enhances the perovskite crystallization, resulting in more stable PVSCs with enhanced power conversion efficiency (PCE) of 18.4%, exceeding the control device PCE (15.5%). Also, we incorporated the above-mentioned SAMs into flexible PVSCs (F-PVSCs) and achieved one of the highest PCE of 16.2% on polyethylene terephthalate (PET) substrate with a remarkable power-per-weight of 26.9 W/g.
159 citations
TL;DR: In this article, the authors investigated the origin of phase segregation and implication for tandems with mixed halide large-bandgap (∼1.75 eV) perovskites and showed explicitly that conduction band electrons or valence band holes are the culprit behind phase segregation.
Abstract: Mixed halide hybrid perovskites are of significant interest because their bandgap can be tuned as a current-matched top-cell in tandem photovoltaics. However, several mixed halide perovskites phase segregate under illumination, exhibit large voltage deficits, and produce unstable photocurrents. We investigate the origin of phase segregation and implication for tandems with mixed halide large-bandgap (∼1.75 eV) perovskites. We show explicitly that MAPb(I0.6Br0.4)3 and (MA0.9,Cs0.1)Pb(I0.6,Br0.4)3, termed “MA” and “MACs”, respectively, rapidly phase segregate in the dark upon 1 sun equivalent current injection. This is direct experimental evidence that conduction band electrons or valence band holes are the culprit behind phase segregation. In contrast, (FA0.83,Cs0.17)Pb(I0.66,Br0.34)3, or “FACs,” prepared at only 75 °C resists phase segregation below 4 sun injection. FACs prepared at 165 °C yields larger grains and withstands higher injected carrier concentrations before phase segregation. The FACs and MAC...
TL;DR: In this article, ascorbic acid (AA) was used as an additive to improve the performance and stability of perovskite solar cells with tin-based solar cells.
TL;DR: A new chemical approach using environmentally friendly strontium chloride (SrCl2 ) as a precursor for perovskite preparation is demonstrated to result in enhanced device performance and stability of the derived hole-conductor-free printable mesoscopic PVSCs.
Abstract: Despite the breakthrough of over 22% power conversion efficiency demonstrated in organic-inorganic hybrid perovskite solar cells (PVSCs), critical concerns pertaining to the instability and toxicity still remain that may potentially hinder their commercialization. In this study, a new chemical approach using environmentally friendly strontium chloride (SrCl2 ) as a precursor for perovskite preparation is demonstrated to result in enhanced device performance and stability of the derived hole-conductor-free printable mesoscopic PVSCs. The CH3 NH3 PbI3 perovskite is chemically modified by introducing SrCl2 in the precursor solution. The results from structural, elemental, and morphological analyses show that the incorporation of SrCl2 affords the formation of CH3 NH3 PbI3 (SrCl2 )x perovskites endowed with lower defect concentration and better pore filling in the derived mesoscopic PVSCs. The optimized compositional CH3 NH3 PbI3 (SrCl2 )0.1 perovskite can substantially enhance the photovoltaic performance of the derived hole-conductor-free device to 15.9%, outperforming the value (13.0%) of the pristine CH3 NH3 PbI3 device. More importantly, the stability of the device in ambient air under illumination is also improved.
TL;DR: In this paper, a bilayer structure of p-type Cu:NiOx nanoparticle-based mesoporous and Cu-doped NiOx blocking layers was developed to achieve efficient charge collection at the NiOx/perovskite interface with minimized recombination loss.
TL;DR: This work implies that Ag incorporation is a feasible route to adjust carrier concentrations in solution-processed perovskite materials in spite of the high concentration of intrinsic defects.
Abstract: Controlled doping for adjustable material polarity and charge carrier concentration is the basis of semiconductor materials and devices, and it is much more difficult to achieve in ionic semiconductors (e.g., ZnO and GaN) than in covalent semiconductors (e.g., Si and Ge), due to the high intrinsic defect density in ionic semiconductors. The organic–inorganic perovskite material, which is frenetically being researched for applications in solar cells and beyond, is also an ionic semiconductor. Here we present the Ag-incorporated organic–inorganic perovskite films and planar heterojunction solar cells. Partial substitution of Pb2+ by Ag+ leads to improved film morphology, crystallinity, and carrier dynamics as well as shifted Fermi level and reduced electron concentration. Consequently, in planar heterojunction photovoltaic devices with inverted stacking structure, Ag incorporation results in an enhancement of the power conversion efficiency from 16.0% to 18.4% in MAPbI3 based devices and from 11.2% to 15.4%...
TL;DR: A new ideal bandgap absorber composition is rationally designed and developed, which possesses lower nonradiative recombination states, band edge disorder, and Urbach energy coupled with a higher absorption coefficient, which yields a reduced Voc,loss and improved PCE for the derived PVSCs.
Abstract: Extremely high power conversion efficiencies (PCEs) of ≈20–22% are realized through intensive research and development of 1.5–1.6 eV bandgap perovskite absorbers. However, development of ideal bandgap (1.3–1.4 eV) absorbers is pivotal to further improve PCE of single junction perovskite solar cells (PVSCs) because of a better balance between absorption loss of sub-bandgap photons and thermalization loss of above-bandgap photons as demonstrated by the Shockley–Queisser detailed balanced calculation. Ideal bandgap PVSCs are currently hindered by the poor optoelectronic quality of perovskite absorbers and their PCEs have stagnated at <15%. In this work, through systematic photoluminescence and photovoltaic analysis, a new ideal bandgap (1.35 eV) absorber composition (MAPb0.5Sn0.5(I0.8Br0.2)3) is rationally designed and developed, which possesses lower nonradiative recombination states, band edge disorder, and Urbach energy coupled with a higher absorption coefficient, which yields a reduced Voc,loss (0.45 V) and improved PCE (as high as 17.63%) for the derived PVSCs. This work provides a promising platform for unleashing the complete potential of ideal bandgap PVSCs and prospects for further improvement.
TL;DR: In this paper, the defect passivation of defect sites in low-bandgap CH3NH3Pb0.5I3 perovskite through the incorporation of fluoroalkyl-substituted fullerene (DF-C60) via a graded heterojunction (GHJ) structure was investigated and reported.
Abstract: Development of low-bandgap (∼1.2 eV) Pb–Sn binary perovskites is exciting and has recently gained immense attention because of their high photovoltages, lowered Pb toxicity, and pivotal role in realizing perovskite tandem solar cells. Defect passivation in this class of perovskite alloys has immense potential to further reduce the photovoltage deficit but is relatively unexplored. Here, we investigate and report the passivation of defect sites in low-bandgap CH3NH3Pb0.5Sn0.5I3 perovskite through the incorporation of fluoroalkyl-substituted fullerene (DF-C60) via a graded heterojunction (GHJ) structure. Graded distribution of DF-C60 successfully reduced the number of trap sites, and the resultant films had characteristically lower Urbach energy, dominant bimolecular recombination, and higher surface/bulk recombination resistance. The improved optoelectronic quality of films with GHJ structure was reflected in improved performance for corresponding photovoltaic devices, with the best PCE up to 15.61% and a ...
TL;DR: In this article, triarylamine-based organic hole-transporting materials (HTMs) are used for improving the efficiency and steady-state performance of perovskite solar cells.
Abstract: 4-Tert-butylpyridine (tBP) is an important additive in triarylamine-based organic hole-transporting materials (HTMs) for improving the efficiency and steady-state performance of perovskite solar ce ...
TL;DR: In this article, a high-performance near-IR (NIR) photodetector using a stable low-bandgap Sn-containing perovskite, (CH3NH3)0.5Pb 0.5Sn 0.6I3, which is processed with an antioxidant additive, ascorbic acid (AA).
Abstract: Photodetectors with ultrafast response are explored using inorganic/organic hybrid perovskites. High responsivity and fast optoelectronic response are achieved due to the exceptional semiconducting properties of perovskite materials. However, most of the perovskite-based photodetectors exploited to date are centered on Pb-based perovskites, which only afford spectral response across the visible spectrum. This study demonstrates a high-performance near-IR (NIR) photodetector using a stable low-bandgap Sn-containing perovskite, (CH3NH3)0.5(NH2CHNH2)0.5Pb0.5Sn0.5I3 (MA0.5FA0.5Pb0.5Sn0.5I3), which is processed with an antioxidant additive, ascorbic acid (AA). The addition of AA effectively strengthens the stability of Sn-containing perovskite against oxygen, thereby significantly inhibiting the leakage current. Consequently, the derived photodetector shows high responsivity with a detectivity of over 1012 Jones ranging from 800 to 970 nm. Such low-cost, solution processable NIR photodetectors with high performance show promising potential for future optoelectronic applications.
TL;DR: In this article, an electrodeposition technique was used to prepare SnO2 films at a reduced temperature below 100 oC, which resulted in high crystallinity and conductivity in addition to high transparency across the visible spectrum.
TL;DR: In this article, a series of hole-transporting materials (HTMs) with small molecular weight are designed, which are constructed on a spiro core involving phenylpyrazole and a second heteroaromatics, i.e., xanthene (O atom), thioxanthene(S atom), and acridine (N atom).
Abstract: Perovskite solar cells have emerged as a promising technique for low-cost, light weight, and highly efficient photovoltaics. However, they still largely rely on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) to serve as hole-transporting materials (HTMs). Here, a series of HTMs with small molecular weight is designed, which are constructed on a spiro core involving phenylpyrazole and a second heteroaromatics, i.e., xanthene (O atom), thioxanthene (S atom), and acridine (N atom). Through varying from phenylpyrazole substituted xanthene (PPyra-XA), thioxanthene (PPyra-TXA), to acridine (PPyra-ACD), their optical and electrochemical properties, hole mobilities, and the photovoltaic performance are optimized. As a consequence, PPyra-TXA based device exhibits the highest power conversion efficiency (PCE) of 18.06%, outperforming that of Spiro-OMeTAD (16.15%), which could be attributed to the enhancement of hole mobility exerted by the thioxanthene. In addition, the dopant-free device shows PCE of 11.7%. These results open a new direction for designing spiro-HTMs by simple modification of chemical structures.
TL;DR: This work stresses the importance of employing a parallel tandem configuration for achieving efficient light harvesting in nonfullerene-based OSCs and provides a useful strategy for exploring the ultimate performance of organic solar cells.
Abstract: In this work, a highly efficient parallel connected tandem solar cell utilizing a nonfullerene acceptor is demonstrated. Guided by optical simulation, each of the active layer thicknesses of subcells are tuned to maximize its light trapping without spending intense effort to match photocurrent. Interestingly, a strong optical microcavity with dual oscillation centers is formed in a back subcell, which further enhances light absorption. The parallel tandem device shows an improved photon-to-electron response over the range between 450 and 800 nm, and a high short-circuit current density (J SC ) of 17.92 mA cm-2 . In addition, the subcells show high fill factors due to reduced recombination loss under diluted light intensity. These merits enable an overall power conversion efficiency (PCE) of >10% for this tandem cell, which represents a ≈15% enhancement compared to the optimal single-junction device. Further application of the designed parallel tandem configuration to more efficient single-junction cells enable a PCE of >11%, which is the highest efficiency among all parallel connected organic solar cells (OSCs). This work stresses the importance of employing a parallel tandem configuration for achieving efficient light harvesting in nonfullerene-based OSCs. It provides a useful strategy for exploring the ultimate performance of organic solar cells.
TL;DR: In this paper, the moisture stability of the widely used cesium and bromide-containing mixed perovskites is carefully studied by characterizing the morphology, crystallization, and device performance before and after the exposure to moisture.
Abstract: The compositional perovskites have attracted broad attention due to the improved photovoltaic performance and enhanced stability compared with the single cation perovskite, such as methylammonium lead iodide and formamidinium lead iodide. In this study, the moisture stability of the widely used cesium and bromide-containing mixed perovskites is carefully studied by characterizing the morphology, crystallization, and device performance before and after the exposure to moisture. Though the mixed perovskites possess strong resistance to moisture in the ambient air, a rapid degradation is observed when the perovskites are exposed to a high relative humidity (RH) up to 70%. The degradation is evidenced by the obvious appearance of CsPbI3 phase along with needle-like morphology after several hours' storage in 70% RH. Moreover, to suppress the erosion of perovskites by the high-level moisture, an interfacial engineering is introduced with phenylethylammonium iodide (PEAI). The PEAI passivation not only shows a retarded degradation but also delivers an enhanced photovoltaic performance from 13% to >17% with much improved stability under high-level moisture. The results imply the efficacy of interfacial engineering in fabricating high-efficiency and stable perovskite solar cells.
TL;DR: In this article, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5-fluoro-2,1,3-benzothiadiazole with different relative amounts of 2,2′-bithiophene (2T), 2T and DTT.
Abstract: All-polymer solar cells (all-PSCs) utilizing p-type polymers as electron-donors and n -typepolymers as electron-acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5-fluoro-2,1,3-benzothiadiazole with different relative amounts of 2,2′-bithiophene (2T) and dithieno[3,2-b;2′,3′-d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide-based polymer acceptor (PNDI) or a [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge-transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI-based all-PSCs than for the conventional PC71BM-based PSCs. As the population of face-on-oriented crystallites of the donor increased in PNDI-based PSC, the short-circuit current density (JSC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all-PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face-on/face-on) is important in all-PSCs because they provide efficient charge transfer at the donor/acceptor interface.
TL;DR: The potential of silicon-organic hybrid (SOH) Mach-Zehnder modulators (MZM) for generating high-speed IM/DD signals at line rates of up to 120 Gbit/s is explored and the highest data rate hitherto achieved with a sub-millimeter MZM on the silicon photonic platform is achieved.
Abstract: High-speed interconnects in data-center and campus-area networks crucially rely on efficient and technically simple transmission techniques that use intensity modulation and direct detection (IM/DD) to bridge distances of up to a few kilometers. This requires electro-optic modulators that combine low operation voltages with large modulation bandwidth and that can be operated at high symbol rates using integrated drive circuits. Here we explore the potential of silicon-organic hybrid (SOH) Mach-Zehnder modulators (MZM) for generating high-speed IM/DD signals at line rates of up to 120 Gbit/s. Using a SiGe BiCMOS signal-conditioning chip, we demonstrate that intensity-modulated duobinary (IDB) signaling allows to efficiently use the electrical bandwidth, thereby enabling line rates of up to 100 Gbit/s at bit error ratios (BER) of 8.5 × 10−5. This is the highest data rate achieved so far using a silicon-based MZM in combination with a dedicated signal-conditioning integrated circuit (IC). We further show four-level pulse-amplitude modulation (PAM4) at lines rates of up to 120 Gbit/s (BER = 3.2 × 10−3) using a high-speed arbitrary-waveform generator and a 0.5 mm long MZM. This is the highest data rate hitherto achieved with a sub-millimeter MZM on the silicon photonic platform.
TL;DR: In this paper, a room-temperature scheme of ligand-promoted formation of high quality perovskite films through the judicious design of nanostructured PbI2·(L)x intermediates, where L denotes the ligand.
Abstract: Recently, organic–inorganic lead halide perovskites have been intensively studied for use in solar cells because of their low cost and high performance. Most of the efficient perovskite solar cells (PVSCs) need layer-dependent high-temperature treatment for each layer of the multilayered structures, increasing the fabrication complexity. In addition, high temperature processes hinder their applications in flexible devices. Therefore, it is highly desirable to develop room-temperature processed methods for controllably forming perovskite films which can simplify the complicated device process and promote emerging flexible device technologies. In this work, we propose a room-temperature scheme of ligand-promoted formation of high quality perovskite films through the judicious design of nanostructured PbI2·(L)x intermediates, where L denotes the ligand. The high quality perovskite films are free of pinholes and impurities, and have high crystallinity. Using our room-temperature crystallization of perovskite films, we have fabricated highly efficient room-temperature solution-processed PVSCs with a power conversion efficiency (PCE) of 17.21% (the current best PVSCs based on perovskite fabricated at room temperature have a PCE of <16%). Meanwhile, we have experimentally investigated the effects of different ligands on building the nanostructured PbI2·(L)x intermediates, and thus the purity, morphology, and optoelectronic performances of the resultant perovskite films. Through thermodynamic and kinetic studies, we theoretically study the reactivity of nanostructured PbI2·(L)x intermediates, thus elucidating the possible mechanism of ligand-promoted perovskite formation. Furthermore, with the experimental and theoretical studies, we establish the selection rules for identifying ideal ligands for the formation of high-quality perovskite films. This work offers a fundamental understanding of ligand effects on the formation of perovskite films for the future design of high-performance and low-cost perovskite-based optoelectronic devices.
TL;DR: In this paper, the authors investigated the correlations among chemical structure, processing, morphology and device performance of PTB7-Th and showed that the regioregularity plays a crucial role in polymer properties as well as the fabrication process of devices.
Abstract: To address the challenges of reliability and facile processability of a benchmark polymer PTB7-Th, one of the most prevailing donor materials utilized in organic solar cells, we have systematically investigated the correlations among chemical structure, processing, morphology and device performance. Our study reveals that the regioregularity of PTB7-Th plays a crucial role in polymer properties as well as the fabrication process of devices. The regioregular polymer entirely consisting of favourable repeat units is capable of realizing high power conversion efficiency (>10%) in organic solar cells without using any solvent additive and tedious processing treatments. More importantly, the device efficiency based on this regioregular polymer is insensitive over a broad range of film thickness (from 100 nm to >400 nm). This will be very advantageous for manufacturing highly efficient and stable polymer solar cells by high throughput fabrication processes.
TL;DR: In this paper, an alcohol-soluble, low-temperature processable and relatively thickness insensitive electron-transporting layer (ETL) comprising a planar coronene derivative, CDIN, was exploited to effectively enhance the photovoltaic performance of various inverted organic OPVs.
TL;DR: A facile solution-processing method to effectively dope versatile n-type organic semiconductors, including fullerene, n- type small molecules, and graphene by commercially available ammonium and phosphonium salts via in situ anion-induced electron transfer is described.
Abstract: In this study, we describe a facile solution-processing method to effectively dope versatile n-type organic semiconductors, including fullerene, n-type small molecules, and graphene by commercially available ammonium and phosphonium salts via in situ anion-induced electron transfer. In addition to the Lewis basicity of anions, we unveiled that the ionic binding strength between the cation and anion of the salts is also crucial in modulating the electron transfer strength of the dopants to affect the resulting doping efficiency. Furthermore, combined with the rational design of n-type molecules, an n-doped organic semiconductor is demonstrated to be thermally and environmentally stable. This finding provides a simple and generally applicable method to make highly efficient n-doped conductors which complements the well-established p-doped organics such as PEDOT:PSS for organic electronic applications.
TL;DR: In this article, a combination of carbon fiber reinforced epoxy and amine curing agent is used to detect barely visible impact damage in composite materials. But the results show that the fluorescence intensity decreases over time; the decrease follows a decay pattern suggesting that the emission comes from a mechanochemically formed radical species which gradually recombines into a non-fluorescent species.