Air-Knife-Assisted Spray Coating of Organic Solar Cells.

The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have risen dramatically since the introduction of the "Y-series" of non-fullerene acceptors. However, the demonstration of rapid scalable deposition techniques to deposit such systems is rare. Here, for the first time, we demonstrate the deposition of a Y-series-based system using ultrasonic spray coating─a technique with the potential for significantly faster deposition speeds than most traditional meniscus-based methods. Through the use of an air-knife to rapidly remove the casting solvent, we can overcome film reticulation, allowing the drying dynamics to be controlled without the use of solvent additives, heating the substrate, or heating the casting solution. The air-knife also facilitates the use of a non-halogenated, low-toxicity solvent, resulting in industrially relevant, spray-coated PM6:DTY6 devices with PCEs of up to 14.1%. We also highlight the obstacles for scalable coating of Y-series-based solar cells, in particular the influence of slower drying times on blend morphology and crystallinity. This work demonstrates the compatibility of ultrasonic spray coating, and use of an air-knife, with high-speed, roll-to-roll OSC manufacturing techniques.

Prospects for Tin-Containing Halide Perovskite Photovoltaics.

Tin-containing metal halide perovskites have enormous potential as photovoltaics, both in narrow band gap mixed tin-lead materials for all-perovskite tandems and for lead-free perovskites. The introduction of Sn(II), however, has significant effects on the solution chemistry, crystallization, defect states, and other material properties in halide perovskites. In this perspective, we summarize the main hurdles for tin-containing perovskites and highlight successful attempts made by the community to overcome them. We discuss important research directions for the development of these materials and propose some approaches to achieve a unified understanding of Sn incorporation. We particularly focus on the discussion of charge carrier dynamics and nonradiative losses at the interfaces between perovskite and charge extraction layers in p-i-n cells. We hope these insights will aid the community to accelerate the development of high-performance, stable single-junction tin-containing perovskite solar cells and all-perovskite tandems.

Chloride-Based Additive Engineering for Efficient and Stable Wide-Bandgap Perovskite Solar Cells.

Metal halide perovskite based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single-junction counterparts. However, overcoming the significant open-circuit voltage deficit present in wide-bandgap perovskite solar cells remains a major hurdle for realizing efficient and stable perovskite tandem cells. Here, a holistic approach to overcoming challenges in 1.8 eV perovskite solar cells is reported by engineering the perovskite crystallization pathway by means of chloride additives. In conjunction with employing a self-assembled monolayer as the hole-transport layer, an open-circuit voltage of 1.25 V and a power conversion efficiency of 17.0% are achieved. The key role of methylammonium chloride addition is elucidated in facilitating the growth of a chloride-rich intermediate phase that directs crystallization of the desired cubic perovskite phase and induces more effective halide homogenization. The as-formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic properties.

Open-circuit and short-circuit loss management in wide-gap perovskite p-i-n solar cells.

In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (VOC) and short-circuit current (JSC) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external VOC is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n-interface, suppressing the QFLS-VOC mismatch, and boosting the VOC. Concurrently, the use of an ionic interlayer or a self-assembled monolayer at the p-interface reduces the inferred field screening induced by mobile ions at JSC, promoting charge extraction and raising the JSC. The combination of the n- and p-type optimizations allows us to approach the thermodynamic potential of the perovskite absorber layer, resulting in 1 cm2 devices with performance parameters of VOCs up to 1.29 V, fill factors above 80% and JSCs up to 17 mA/cm2, in addition to a thermal stability T80 lifetime of more than 3500 h at 85 °C.

Synergistic Surface Modification of Tin-Lead Perovskite Solar Cells.

Interfaces in thin-film photovoltaics play a pivotal role in determining device efficiency and longevity. In this work, the top surface treatment of mixed tin-lead (≈1.26 eV) halide perovskite films for p-i-n solar cells is studied. Charge extraction is promoted by treating the perovskite surface with piperazine. This compound reacts with the organic cations at the perovskite surface, modifying the surface structure and tuning the interfacial energy level alignment. In addition, the combined treatment with C60 pyrrolidine tris-acid (CPTA) reduces hysteresis and leads to efficiencies up to 22.7%, with open-circuit voltage values reaching 0.90 V, ≈92% of the radiative limit for the bandgap of this material. The modified cells also show superior stability, with unencapsulated cells retaining 96% of their initial efficiency after >2000 h of storage in N2 and encapsulated cells retaining 90% efficiency after >450 h of storage in air. Intriguingly, CPTA preferentially binds to Sn2+ sites at film surface over Pb2+ due to the energetically favored exposure of the former, according to first-principles calculations. This work provides new insights into the surface chemistry of perovskite films in terms of their structural, electronic, and defect characteristics and this knowledge is used to fabricate state-of-the-art solar cells.

Controlling anisotropic properties by manipulating the orientation of chiral small molecules.

Chiral π-conjugated molecules bring new functionality to technological applications and represent an exciting, rapidly expanding area of research. Their functional properties, such as the absorption and emission of circularly polarized light or the transport of spin-polarized electrons, are highly anisotropic. As a result, the orientation of chiral molecules critically determines the functionality and efficiency of chiral devices. Here we present a strategy to control the orientation of a small chiral molecule (2,2'-dicyano[6]helicene) by the use of organic and inorganic templating layers. Such templating layers can either force 2,2'-dicyano[6]helicene to adopt a face-on orientation and self-assemble into upright supramolecular columns oriented with their helical axis perpendicular to the substrate, or an edge-on orientation with parallel-lying supramolecular columns. Through such control, we show that low- and high-energy chiroptical responses can be independently 'turned on' or 'turned off'. The templating methodologies described here provide a simple way to engineer orientational control and, by association, anisotropic functional properties of chiral molecular systems for a range of emerging technologies.

Exploring Nanoscale Structure in Perovskite Precursor Solutions Using Neutron and Light Scattering.

Tailoring the solution chemistry of metal halide perovskites requires a detailed understanding of precursor aggregation and coordination. In this work, we use various scattering techniques, including dynamic light scattering (DLS), small angle neutron scattering (SANS), and spin-echo SANS (SESANS) to probe the nanostructures from 1 nm to 10 µm within two different lead-halide perovskite solution inks (MAPbI3 and a triple-cation mixed-halide perovskite). We find that DLS can misrepresent the size distribution of the colloidal dispersion and use SANS/SESANS to confirm that these perovskite solutions are mostly comprised of 1-2 nm-sized particles. We further conclude that if there are larger colloids present, their concentration must be <0.005% of the total dispersion volume. With SANS, we apply a simple fitting model for two component microemulsions (Teubner-Strey), demonstrating this as a potential method to investigate the structure, chemical composition, and colloidal stability of perovskite solutions, and we here show that MAPbI3 solutions age more drastically than triple cation solutions.

Gas-Assisted Spray Coating of Perovskite Solar Cells Incorporating Sprayed Self-Assembled Monolayers.

Self-assembled monolayers (SAMs) are becoming widely utilized as hole-selective layers in high-performance p-i-n architecture perovskite solar cells. Ultrasonic spray coating and airbrush coating are demonstrated here as effective methods to deposit MeO-2PACz; a carbazole-based SAM. Potential dewetting of hybrid perovskite precursor solutions from this layer is overcome using optimized solvent rinsing protocols. The use of air-knife gas-quenching is then explored to rapidly remove the volatile solvent from an MAPbI3 precursor film spray-coated onto an MeO-2PACz SAM, allowing fabrication of p-i-n devices with power conversion efficiencies in excess of 20%, with all other layers thermally evaporated. This combination of deposition techniques is consistent with a rapid, roll-to-roll manufacturing process for the fabrication of large-area solar cells.

Perovskites on Ice: An Additive-Free Approach to Increase the Shelf-Life of Triple-Cation Perovskite Precursor Solutions.

Invited for this month's cover is the group of David Lidzey at the University of Sheffield. The image shows a futuristic view of large-scale perovskite solar cell (PSC) manufacture. This includes a high-volume roll-to-roll printing facility and cold-storage of PSC precursor solutions in large industrial fridges. The Full Paper itself is available at 10.1002/cssc.202100332.

Perovskites on Ice: An Additive-Free Approach to Increase the Shelf-Life of Triple-Cation Perovskite Precursor Solutions.

The development of stable perovskite precursor solutions is critical if solution-processable perovskite solar cells (PSCs) are to be practically manufacturable. Ideally, such precursors should combine high solution stability without using chemical additives that might compromise PSC performance. Here, it was shown that the shelf-life of high-performing perovskite precursors could be greatly improved by storing solutions at low-temperature without the need to alter chemical composition. Devices fabricated from solutions stored for 31 days at 4 °C achieved a champion power conversion efficiency (PCE) of 18.6 % (97 % of original PCE). The choice of precursor solvent also impacted solution shelf-life, with DMSO-based solutions having enhanced solution stability compared to those including DMF. The compositions of aged precursors were explored using NMR spectroscopy, and films made from these solutions were analysed using X-ray diffraction. It was concluded that the improvement in precursor solution stability is directly linked to the suppression of an addition-elimination reaction and the preservation of higher amounts of methylammonium within solution.

Emissive spin-0 triplet-pairs are a direct product of triplet-triplet annihilation in pentacene single crystals and anthradithiophene films.

Singlet fission and triplet-triplet annihilation represent two highly promising ways of increasing the efficiency of photovoltaic devices. Both processes are believed to be mediated by a biexcitonic triplet-pair state, 1(TT). Recently however, there has been debate over the role of 1(TT) in triplet-triplet annihilation. Here we use intensity-dependent, low-temperature photoluminescence measurements, combined with kinetic modelling, to show that distinct 1(TT) emission arises directly from triplet-triplet annihilation in high-quality pentacene single crystals and anthradithiophene (diF-TES-ADT) thin films. This work demonstrates that a real, emissive triplet-pair state acts as an intermediate in both singlet fission and triplet-triplet annihilation and that this is true for both endo- and exothermic singlet fission materials.

Monolithic perovskite/silicon tandem solar cell with >29% efficiency by enhanced hole extraction.

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.

Development of Spray-Coated Perovskite Solar Cells.

Over the past six years, researchers have investigated the use of spray coating to fabricate perovskite solar cells (PSCs), with the aim of demonstrating its viability as an industrial manufacturing process. This spotlight on applications outlines the key benefits of this coating technology and summarizes progress made to date, with attention focused on varied efforts to control the crystallization and uniformity of the perovskite layer. The emerging understanding of processes required to create smooth, dense spray-cast perovskite films has recently led to the demonstration of fully spray-cast PSCs with a power conversion efficiency of 19.4%.

Rapid Scalable Processing of Tin Oxide Transport Layers for Perovskite Solar Cells.

The development of scalable deposition methods for perovskite solar cell materials is critical to enable the commercialization of this nascent technology. Herein, we investigate the use and processing of nanoparticle SnO2 films as electron transport layers in perovskite solar cells and develop deposition methods for ultrasonic spray coating and slot-die coating, leading to photovoltaic device efficiencies over 19%. The effects of postprocessing treatments (thermal annealing, UV ozone, and O2 plasma) are then probed using structural and spectroscopic techniques to characterize the nature of the np-SnO2/perovskite interface. We show that a brief "hot air flow" method can be used to replace extended thermal annealing, confirming that this approach is compatible with high-throughput processing. Our results highlight the importance of interface management to minimize nonradiative losses and provide a deeper understanding of the processing requirements for large-area deposition of nanoparticle metal oxides.

Fully Spray-Coated Triple-Cation Perovskite Solar Cells.

We use ultrasonic spray-coating to sequentially deposit thin films of tin oxide, a triple-cation perovskite and spiro-OMeTAD, allowing us fabricate perovskite solar cells (PSCs) with a champion reverse scan power conversion efficiency (PCE) of 19.4% on small-area substrates. We show that the use of spray-deposition permits us to rapidly (>80 mm s-1) coat 25 mm × 75 mm substrates that were divided into a series of devices each with an active area of 15.4 mm2, yielding an average PCE of 10.3% and a peak PCE of 16.3%. By connecting seven 15.4 mm2 devices in parallel on a single substrate, we create a device having an effective active area of 1.08 cm2 and a PCE of 12.7%. This work demonstrates the possibility for spray-coating to fabricate high efficiency and low-cost perovskite solar cells at speed.

Controversies in the surgical management of sporadic medullary thyroid carcinoma.

PURPOSE OF REVIEW: Medullary thyroid carcinoma (MTC) represents a wide spectrum of tumours with differing biology, behaviour and natural history. The only current available curative treatment is surgery in the form of thyroidectomy with or without ipsilateral or bilateral neck dissection. There is a lack of consensus in the available published guidelines on the optimum extent of initial surgery, and there is significant variation in clinical practice. This review focuses on the most recently published evidence. RECENT FINDINGS: Many patients with limited disease do not receive total thyroidectomy and central neck compartment dissection as recommended by international guidelines. Despite this, 5-year disease-specific survival is over 90% in those without distant metastases at presentation. Over 20% of patients may harbour occult lateral compartment nodal metastases, and baseline calcitonin alone (>1000 pg/ml) is not a good predictor of nodal metastasis. Although delayed lateral neck compartment dissection results in similar survival outcomes to prophylactic neck dissection for clinically node-negative patients, there is an underappreciated psychological effect of having biochemical evidence of persistent disease following limited surgery. SUMMARY: No single currently available prognostic indicator is sufficient to predict disease behaviour and evidence of occult nodal metastases. In clinically ad radiologically node-negative patients, the extent of neck dissection at initial operation, therefore, needs to be planned and executed on an individual patient basis.

Potassium iodide reduces the stability of triple-cation perovskite solar cells.

The addition of alkali metal halides to hybrid perovskite materials can significantly impact their crystallisation and hence their performance when used in solar cell devices. Previous work on the use of potassium iodide (KI) in active layers to passivate defects in triple-cation mixed-halide perovskites has been shown to enhance their luminescence efficiency and reduce current-voltage hysteresis. However, the operational stability of KI passivated perovskite solar cells under ambient conditions remains largely unexplored. By investigating perovskite solar cell performance with SnO2 or TiO2 electron transport layers (ETL), we propose that defect passivation using KI is highly sensitive to the composition of the perovskite-ETL interface. We reconfirm findings from previous reports that KI preferentially interacts with bromide ions in mixed-halide perovskites, and - at concentrations >5 mol% in the precursor solution - modifies the primary absorber composition as well as leading to the phase segregation of an undesirable secondary non-perovskite phase (KBr) at high KI concentration. Importantly, by studying both material and device stability under continuous illumination and bias under ambient/high-humidity conditions, we show that this secondary phase becomes a favourable degradation product, and that devices incorporating KI have reduced stability.

High-Efficiency Spray-Coated Perovskite Solar Cells Utilizing Vacuum-Assisted Solution Processing.

We use ultrasonic spray-coating to fabricate cesium-containing triple-cation perovskite solar cells with a power-conversion efficiency of up to 17.8%. Our fabrication route involves a brief exposure of the partially wet spray-cast films to a low vacuum, a process that is used to control film crystallization. We show that films that are not vacuum-exposed are relatively rough and inhomogeneous, while vacuum-exposed films are smooth and consist of small and densely packed perovskite crystals. The process techniques developed here represent a step toward a scalable and industrially compatible manufacturing process capable of creating stable and high-performance perovskite solar cells.

Age is not a predictor of prognosis in metastatic cutaneous squamous cell carcinoma of the head and neck.

BACKGROUND: Metastatic cutaneous squamous cell carcinoma of the head and neck (cHNSCC) is more common in older patients. It is postulated that the age-related decline in immunity plays a role in cancer predisposition and prognosis. We aimed to investigate the effect of age on outcomes in cHNSCC and compare these with the outcomes of patients with cHNSCC and known immunosuppression. METHODS: Patients with metastatic cHNSCC treated with curative intent were identified from a prospectively collated database of head and neck cancers at the Sydney Head and Neck Cancer Institute. Patients with cHNSCC with known immunosuppression provided a comparison group for analysis of disease-specific outcomes. RESULTS: The study cohort includes 418 immunocompetent patients with metastatic cHNSCC (median age: 73 years (interquartile range: 65-81 years)) and the control cohort includes 24 patients with metastatic cHNSCC and immunosuppression (median age: 51 years (interquartile range: 42-62 years)). Increasing age was not associated with poorer disease-free or disease-specific survival. Patients in older age groups (70 years and over) had better disease-specific outcomes than patients with long-term immunosuppression. Patterns of disease failure did not differ between different age groups. The number of positive nodes and extra-capsular spread were the only significant prognostic variables in multivariable analysis. CONCLUSION: In the context of metastatic cHNSCC, age should not be considered as a marker of poor prognosis. Age should not be considered a surrogate marker of immune function considering the poorer outcomes seen in patients with immunosuppression. Older patients with metastatic cHNSCC should be considered candidates for standard treatment if otherwise medically fit.