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Enhancing the passivation of the perovskite (PVK)/charge transport layer interface is the primary strategy for minimizing losses in the open circuit voltage of PVK solar cells. We examined systems comprising half-stacks of hole transport layers (HTLs) deposited atop the mixed cation lead halide PVK photoactive layer (Cs0.05FA0.85MA0.1PbI3) using time-resolved photoluminescence and transient absorption spectroscopy. Photovoltaic devices were constructed to validate our findings, yielding power conversion efficiencies of up to 24%. Combining spectroscopic measurements reflected the complexity associated with interpretation of the kinetics as multiple processes overlap over time. The 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) HTL resulted in low interface recombination and effective charge extraction, whereas poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibited high interface recombination. The NiOxHTL passivated with [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) exhibited prolonged photoluminescence carrier lifetimes, signifying interface passivation through a Me-4PACz self-assembled monolayer. Theoretical calculations demonstrated an electrostatic interaction between Me-4PACz and the iodine vacancies at the PVK interface, indicating defect passivation.

Compressive strain engineering improves perovskite stability. Two-dimensional compressive strain along the in-plane direction can be applied to perovskites through the substrate; however, this in-plane strain results in an offsetting tensile strain perpendicular to the substrate, linked to the positive Poisson ratio of perovskites. Substrate-induced strain engineering has not yet resulted in state-of-the-art operational stability. Here, we seek instead to implement hydrostatic strain in perovskites by embedding lattice-mismatched perovskite quantum dots (QDs) into a perovskite matrix. QD-in-matrix perovskites show a homogeneously strained lattice as evidenced by grazing-incidence X-ray diffraction. We fabricate mixed-halide wide-band-gap (Eg; 1.77 eV) QD-in-matrix perovskite solar cells that maintain >90% of their initial power conversion efficiency (PCE) after 200 h of one-sun operation at the maximum power point (MPP), a significant improvement relative to matrix-only devices, which lose 10% (relative) of their initial PCE after 5 h of MPP tracking.

AbstractHuman Norovirus belongs to a family Calciviridae, and was identified in the outbreak of gastroenteritis in Norwalk, due to its seasonal prevalence known as “winter vomiting disease.” Treatment of Norovirus infection is still mysterious because there is no effective antiviral drugs or vaccine developed to protect against the infection, to eradicate the infection an effective vaccine should be developed. In this study, capsid protein (A7YK10), small protein (A7YK11), and polyprotein (A7YK09) were utilized. These proteins were subjected to B and T cell epitopes prediction by using reliable immunoinformatics tools. The antigenic and non-allergenic epitopes were selected for the subunit vaccine, which can activate cellular and humoral immune responses. Linkers joined these epitopes together. The vaccine structure was modelled and validated by using Errat, ProSA, and rampage servers. The modelled vaccine was docked with TLR-7. The stability of the docked complex was evaluated by MD simulation. To apply the concept in a wet lab, the reverse translated vaccine sequence was cloned in pET28a (+). The vaccine developed in this study requires experimental validation to ensure its effectiveness against the disease.Communicated by Ramaswamy H. Sarma

Stacking perovskite solar cells onto crystalline silicon bottom cells in a monolithic tandem configuration enables power-conversion efficiencies (PCEs) well above those of their single-junction counterparts. However, state-of-the-art wide-band-gap perovskite films suffer from phase stability issues. Here, we show how carbazole as an additive to the perovskite precursor solution can not only reduce nonradiative recombination losses but, perhaps more importantly, also can suppress phase segregation under exposure to moisture and light illumination. This enables a stabilized PCE of 28.6% (independently certified at 28.2%) for a monolithic perovskite/silicon tandem solar cell over ∼1 cm2and 27.1% over 3.8 cm2, built from a textured silicon heterojunction solar cell. The modified tandem devices retain ∼93% of their performance over 43 days in a hot and humid outdoor environment of almost 100% relative humidity over 250 h under continuous 1-sun illumination and about 87% during a 85/85 damp-heat test for 500 h, demonstrating the improved phase stability.

In bulk heterojunction (BHJ) organic solar cells (OSCs) both the electron affinity (EA) and ionization energy (IE) offsets at the donor–acceptor interface should equally control exciton dissociation. Here, we demonstrate that in low-bandgap non-fullerene acceptor (NFA) BHJs ultrafast donor-to-acceptor energy transfer precedes hole transfer from the acceptor to the donor and thus renders the EA offset virtually unimportant. Moreover, sizeable bulk IE offsets of about 0.5 eV are needed for efficient charge transfer and high internal quantum efficiencies, since energy level bending at the donor–NFA interface caused by the acceptors’ quadrupole moments prevents efficient exciton-to-charge-transfer state conversion at low IE offsets. The same bending, however, is the origin of the barrier-less charge transfer state to free charge conversion. Our results provide a comprehensive picture of the photophysics of NFA-based blends, and show that sizeable bulk IE offsets are essential to design efficient BHJ OSCs based on low-bandgap NFAs.

Non-fullerene acceptor (NFA)-based organic solar cells have outperformed fullerene-based devices, yet their photophysics is less well understood. Herein, changes in the donor polymer backbone sidechain substitution and backbone fluorination in benzodithiophene–thiophene copolymers are linked to the photophysical processes and performance of bulk heterojunction (BHJ) solar cells using ITIC as the NFA. Increased geminate recombination is observed when the donor polymer is alkoxy-substituted in conjunction with faster nongeminate recombination of free charges, limiting both the short-circuit current and device fill factor (FF). In contrast, thienyl-substitution reduces geminate recombination, albeit nongeminate recombination remains significant, leading to improved short-circuit current density, yet not the FF. Only the combination of thienyl-substitution and polymer backbone fluorination yields both efficient charge separation and significantly reduced nongeminate recombination, resulting in FFs in excess of 60%. Time-delayed collection field measurements ascertain that charge generation is field independent in the thienyl-substituted donor polymer:ITIC systems, whereas weakly field dependent in the alkoxy-substituted polymer:ITIC blend, indicating that the low FFs are primarily caused by nongeminate recombination. This work provides insight into the interplay of donor polymer structure, BHJ photophysics, and device performance for a prototypical NFA, namely, ITIC. More specifically, it links the donor polymer chemical structure to quantifiable changes of kinetic parameters and the yield of individual processes in ITIC-based BHJ blends.

The formation of different types of structural polymorphs of poly(3-hexyl-thiophene) (P3HT) affects the performance of organic photovoltaic (OPV) devices that use thermally annealed P3HT:PCBM[60] blend films as a photoactive layer. Here it is demonstrated that when densely packed and nondensely packed P3HT polymorphs coexist in the P3HT:PCBM[60] layer, nongeminate charge recombination is fast; however, in a device nongeminate recombination is effectively overruled by efficient and fast charge carrier extraction. In stark contrast, when only a less densely packed P3HT polymorph is present in the blend, nongeminate charge recombination losses are less pronounced, and the charge carrier extraction efficiency is lower. The antagonistic nongeminate charge recombination and charge carrier extraction processes in these systems are monitored by time-delayed collection field (TDCF) and ultrafast transient absorption (TA) experiments. Furthermore, resonance Raman spectroscopy reveals that in the absence of the densely packed P3HT polymorph the energetic disorder present in the P3HT:PCBM[60] blend is higher. High-resolution atomic force microscopy imaging further identifies pronounced differences in the layer morphology when the polymorph distribution varies between unimodal and bimodal. These results indicate that less densely packed P3HT polymorphs increase disorder and impede charge collection, leading to a reduction of the device fill factor.

We explored for the first time the ultrafast carrier trapping of a metal-doped titanium dioxide (TiO2) semiconductor using broad-band transient absorption (TA) spectroscopy with 120 fs temporal resolution. Titanium dioxide was successfully doped layer-by-layer with two metal ions, namely tungsten and cobalt. The time-resolved data demonstrate clearly that the carrier trapping time decreases progressively as the doping concentration increases. A global-fitting procedure for the carrier trapping suggests the appearance of two time components: a fast one that is directly associated with carrier trapping to the defect state in the vicinity of the conduction band and a slow one that is attributed to carrier trapping to the deep-level state from the conduction band. With a relatively long doping deposition time on the order of 30 s, a carrier lifetime of about 1 ps is obtained. To confirm that the measured ultrafast carrier dynamics are associated with electron trapping by metal doping, we explored the carrier dynamics of undoped TiO2. The findings reported here may be useful for the implementation of high-speed optoelectronic applications and fast switching devices.

Fluorescence enhancement of organic fluorophores shows tremendous potential to improve image contrast in fluorescence-based bioimaging. Here, we present an experimental study of the interaction of two cationic porphyrins, meso-tetrakis(1-methylpyridinium-4-yl)porphyrin chloride (TMPyP) and meso-tetrakis(4-N,N,N-trimethylanilinium)porphyrin chloride (TMAP), with cationic surfactant-stabilized zinc oxide nanoparticles (ZnO NPs) based on several steady-state and time-resolved techniques. We show the first experimental measurements demonstrating a clear transition from pronounced fluorescence enhancement to charge transfer (CT) complex formation by simply changing the nature and location of the positive charge of the meso substituent of the cationic porphyrins. For TMPyP, we observe a sixfold increase in the fluorescence intensity of TMPyP upon addition of ZnO NPs. Our experimental results indicate that the electrostatic binding of TMPyP with the surface of ZnO NPs increases the symmetry of the porphyrin macrocycle. This electronic communication hinders the rotational relaxation of the meso unit and/or decreases the intramolecular CT character between the cavity and the meso substituent of the porphyrin, resulting in the enhancement of the intensity of the fluorescence. For TMAP, on the other hand, the different type and nature of the positive charge resulting in the development of the CT band arise from the interaction with the surface of ZnO NPs. This observation is confirmed by the femtosecond transient absorption spectroscopy, which provides clear spectroscopic signatures of photoinduced electron transfer from TMAP to ZnO NPs.

Interfaces in metal halide perovskite (MHP) solar cells cause carrier recombination and thereby reduce their power conversion efficiency. Here, ultrafast (picosecond to nanosecond) transient reflection (TR) spectroscopy has been used to probe interfacial carrier dynamics in thin films of the reference MHP MAPbI3and state-of-the-art (Cs0.15MA0.15FA0.70)Pb(Br0.20I0.80)3(CsFAMA). First, MAPbI3films in contact with fullerene-based charge extraction layers (CTLs) in the presence and absence of LiF used as an interlayer (ITL) were studied. To quantify and discriminate between interface-induced and bulk carrier recombination, we employed a one-dimensional diffusion and recombination model. The interface-induced carrier recombination velocity was found to be 1229 ± 78 cm s–1in nonpassivated MAPbI3films, which was increased to 2248 ± 75 cm s–1when MAPbI3interfaced directly with C60, whereas it was reduced to 145 ± 63 cm s–1when inserting a 1 nm thin LiF interlayer between MAPbI3and C60, in turn improving the open-circuit voltage of devices by 33 mV. Second, the effect of surface and grain boundary passivation by PhenHCl in CsFAMA was revealed. Here, the recombination velocity decreased from 605 ± 52 to 0.16 ± 5.28 and 7.294 ± 34.5 cm s–1, respectively. The approach and data analysis presented here are immediately applicable to other perovskite/interlayer/CTL interfaces and passivation protocols, and they add to our understanding of the impact of surfaces and interfaces in MHP-based thin films on carrier recombination and device efficiency.

Accurate reproduction of a preoperative plan is critical in wide resection of bone sarcomas. Recent advances in computer navigation and 3D-custom jigs have increased resection accuracy, although with certain practical drawbacks.

Despite impressive power conversion efficiencies (PCEs) reported for lab-scale perovskite solar cells (PSCs), obtaining large-area devices with similar performance remains challenging. Fundamentally, this can largely be attributed to a polarity mismatch between the perovskite-precursor solution and the underlying hydrophobic contact materials, resulting in perovskite films of insufficient quality for scaled devices. Specifically, for p-i-ndevices, the commonly used DMF/DMSO co-solvent has a significant polarity mismatch with its underlying hole-transporting layer, PTAA. Here, the role of MAPbI3•solvent adduct interaction with the PTAA surface towards the formation of micro- and nano-scale pinholes is elucidated in detail. Replacing DMSO with NMP in the co-solvent system changes the binding energy profoundly, enabling uniform and dense films over large areas. The PCE of DMF/NMP ink-based devices drops slightly with increasing active device area, from 21.5% (0.1 cm2) to 19.8% (6.8 cm2), in comparison with conventional DMF/DMSO ink. This work opens a pathway towards the scalability of solution-processed perovskite optoelectronic devices.

Neuromorphic computing has the potential to address the inherent limitations of conventional integrated circuit technology, ranging from perception, pattern recognition, to memory and decision-making (Acc. Chem. Res.2019, 52(4), 964−974) (Nature2004, 431(7010), 796−803) (Nat. Nanotechnol.2013, 8(1), 13−24). Despite their low power consumption (Nano Lett.2016, 16(11), 6724−6732), traditional two-terminal memristors can perform only a single function while lacking heterosynaptic plasticity (Nanotechnology2013, 24(38), 382001). Inspired by the unconditioned reflex, multiterminal memristive transistors (memtransistor) were developed to realize complex functions, such as multiterminal modulation and heterosynaptic plasticity (Nature2018, 554, (7693), 500−504). Here we combine a hybrid metal halide perovskite with an organic conjugated polymer to form heterojunction transistors that are responsive to both electrical and optical stimuli. We show that the synergistic effects of photoinduced ion migration in the perovskite and electronic transport in the polymer layers can be exploited to realize memristive functions. The device combines reversible, nonvolatile conductance modulation with large switching current ratios, high endurance, and long retention times. Using in situ scanning Kelvin probe microscopy and variable-temperature charge transport measurement, we correlate the collective effects of bias-induced and photoinduced ion migration with the heterosynaptic behavior observed in this hybrid memtransistor. The hybrid heterojunction channel concept is expected to be applicable to other material combinations making it a promising platform for deployment in innovative neuromorphic devices of the future.

The role of residual lead iodide on the photophysical properties of methylammonium lead iodide is still unclear and contradictory views exist about its impact. Herein, it is reported that there is a critical amount of residual lead iodide, which is beneficial for the solar cell performance. Transient absorption spectroscopy is used to investigate the charge carrier recombination dynamics in perovskite solar cells and to address the role of different amounts of residual lead iodide. The amount of lead iodide is varied through the perovskite thin film preparation protocol upon a modified two‐step fabrication process. Slower carrier dynamics are observed at the perovskite/titanium dioxide interface in the presence of residual lead iodide when exciting the perovskite at the perovskite/titanium interface, which correlates with improved solar cell device performance. Excitation from the perovskite side indicates that the effect of residual lead iodide is primarily at the titanium dioxide interface. Increasing the lead iodide content does not further alter the carrier recombination; on the contrary, it results in lower device performance. This study confirms that the presence of lead iodide can have a beneficial effect, as it reduces charge carrier recombination at the perovskite/titanium dioxide interface. Moderate amount of residual lead iodide is beneficial for perovskite solar cells as shown by transient absorption spectroscopy. More specifically, photoexcitation from the perovskite/titanium dioxide (TiO2) side shows retarded charge carrier recombination at the interface.