Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

We demonstrate that local and long-range orders of poly­(3-hexylthiophene) (P3HT) semicrystalline films can be synergistically improved by combining chemical functionalization of the substrate with solution-state disentanglement and preaggregation of P3HT in a θ solvent, leading to a very significant enhancement of the field effect carrier mobility. The preaggregation and surface functionalization effects combine to enhance the carrier mobility nearly 100-fold as compared with standard film preparation by spin-coating, and nearly 10-fold increase over the benefits of preaggregation alone. In situ quartz crystal microbalance with dissipation (QCM-D) experiments reveal enhanced deposition of preaggregates on surfaces modified with an alkyl-terminated self-assembled monolayer (SAM) in comparison to unaggregated polymer chains in the same conditions. Additional measurements reveal the combined preaggregation and surface functionalization significantly enhances local order of the conjugated polymer through planarization and extension of the conjugated backbone of the polymer which clearly translate to significant improvements of carrier transport at the semiconductor–dielectric interface in organic thin film transistors. This study points to opportunities in combining complementary routes, such as well-known preaggregation with substrate chemical functionalization, to enhance the polymer self-assembly and improve its interfacial order with benefits for transport properties

Stable High-Performance Flexible Photodetector Based on Upconversion Nanoparticles/Perovskite Microarrays Composite

Methylammonium lead halide perovskite has emerged as a new class of low-temperature-processed high-performance semiconductors for optoelectronics, but with photoresponse limited to the UV–visible region and low environmental stability. Herein, we report a flexible planar photodetector based on MAPbI₃ microarrays integrated with NaYF₄:​Yb/​Er upconversion nanoparticles (UCns) that offers promise for future high performance and long-term environmental stability. The promise derives from the confluence of several factors, including significantly enhanced photons absorption in the visible spectrum, efficient energy transition in the near-infrared (NIR) region, and inhibition of water attack by the hydrophobic UCns capping layer. The UCns layer aided in remarkably enhanced photodetection capability in the visible spectrum with detectivity (<i>D*</i>) reaching 5.9 × 10¹² Jones, among the highest reported values, due to the increased photocarrier lifetime and decreased reflectivity. Excellent NIR photoresponse with spectral responsivity (<i>R</i>) and <i>D*</i> as high as 0.27 A W^–1 and 0.76 × 10¹² Jones were obtained at 980 nm, respectively, superior to the reported values of state-of-the-art organic-perovskite NIR photodetectors. Moreover, the hydrophobic UCns capping layer serving as a moisture inhibitor allowed significantly enhanced long-term environmental stability, e.g., 70% vs 27% performance retained after 1000 h exposure in 30–40% RH humidity air without encapsulation for the bilayer and the neat MAPbI₃ devices, respectively. These results suggest that the composite based on perovskite and UCns is promising for constructing high-performance broadband optoelectronic devices with long-term stability

Molecularly Functionalized SnO₂ Films by Carboxylic Acids for High-Performance Perovskite Solar Cells

Metal oxides are commonly employed as electron transport layers (ETLs) for n-i-p perovskite solar cells (PSCs), but the presence of surface traps and their mismatched energy alignment with perovskites limits the corresponding device performance. Therefore, the interfacial modification of ETLs by functional molecules becomes an important strategy for tailoring the interfacial properties and facilitating an efficient charge extraction and transport in PSCs. However, an in-depth understanding of the influences of their molecular structures on the surface chemistry and electronic properties of ETLs is rarely discussed. Herein, three carboxylic acid-based molecules with different chemical structures were employed to modify the SnO2 ETL and their effects on the performance of PSCs were systematically investigated. We found that the alkyl-chain length and carboxyl number in molecular structures can dramatically alter their binding strength to SnO2, providing a good strategy to fine-tune their film quality, electron mobility, and energy offset at the cathode interface. Benefiting from the optimal coordination ability of citric acid (CA) to SnO2, the corresponding PSCs show better charge transport properties and suppressed nonradiative recombination, leading to a champion efficiency of 23.1% with much improved environmental stability, highlighting the potential of rational design of molecular modifiers for high-performance ETLs applied in PSCs

Stereoselective Fluorosulfonylation of Vinylboronic Acids for (<i>E</i>)‑Vinyl Sulfonyl Fluorides with Copper Participation

A practical synthetic method for the synthesis of vinyl sulfonyl fluorides through copper-promoted direct fluorosulfonylation has been developed. The reaction of the vinylboronic acids with DABSO and then NFSI is performed under mild reaction conditions. This transformation efficiently affords aryl or alkyl vinyl sulfonyl fluorides with good reaction yields, exclusive E-configuration, broad substrate scope, excellent compatibility, and operational simplicity

Blade-Coated Hybrid Perovskite Solar Cells with Efficiency > 17%: An In Situ Investigation

Blade-coating has recently emerged as a scalable fabrication method for hybrid perovskite solar cells, but it currently underperforms spin-coating, yielding a power conversion efficiency (PCE) of ∼15% for CH₃NH₃PbI₃ (MAPbI₃). We investigate the solidification of MAPbI₃ films in situ during spin/blade-coating using optical and X-ray scattering methods. We find that the coating method and conditions profoundly influence the crystallization process, which proceeds through intermediate crystalline solvates. The polymorphism and composition of the solvates are mediated by the solvent removal rate dictated by the process temperature in blade-coating. Low to intermediate temperatures (25–80 °C) yield solvates with differing compositions and yield poor PCEs (∼5–8%) and a large spread (±2.5%). The intermediate solvates are not observed at elevated temperatures (>100 °C), pointing to direct crystallization of the perovskite from the sol–gel ink. These conditions yield large and compact spherulitic domains of perovskite and improve the PCE to ∼13–15% with a narrower spread (< ± 0.5%), while coating at 150 °C yields 17.5% solar cells by inducing in situ decomposition of a small amount of MAPbI₃ into PbI₂. The insights into the crystallization pathway highlight the current challenges and future opportunities associated with scaling up hybrid perovskite solar cell manufacturing

Highly Efficient Ruddlesden–Popper Halide Perovskite PA₂MA₄Pb₅I₁₆ Solar Cells

Two-dimensional (2D) Ruddlesden–Popper (RP) organic–inorganic perovskites have emerged as promising candidates for solar cells with technologically relevant stability. Herein, a new RP perovskite, the fifth member (⟨<i>n</i>⟩ = 5) of the (CH₃(CH₂)₂NH₃)₂(CH₃NH₃)_<i>n</i>−1Pb_<i>n</i>I_3<i>n</i>+1 family (abbreviated as PA₂MA₄Pb₅I₁₆), was synthesized and systematically investigated in terms of photovoltaic application. The obtained pure PA₂MA₄Pb₅I₁₆ crystal exhibits a direct band gap of <i>E</i>_g = 1.85 eV. Systematic analysis on the solid film highlights the key role of the precursor–solvent interaction in the quantum well orientation, phase purity, grain size, surface quality, and optoelectronic properties, which can be well-tuned with addition of dimethyl sulfoxide (DMSO) into the <i>N</i>,<i>N</i>-dimethylformamide (DMF) precursor solution. These findings present opportunities for designing a high-quality RP film with well-controlled quantum well orientation, micrometer-sized grains, and optoelectronic properties. As a result, we achieved power conversion efficiency (PCE) up to 10.41%

Increasing H‑Aggregates via Sequential Aggregation to Enhance the Hole Mobility of Printed Conjugated Polymer Films

Solid-state microstructures of conjugated polymers are essential for charge transport in electronic devices. However, precisely modulating aggregation pathways of conjugated polymers in a controlled fashion is challenging. Herein, we report a sequential aggregation approach via selectively modulating side chain aggregation in solution state and backbone aggregation during film formation to increase H-aggregates and consequently enhance hole mobility of printed diketopyrrolopyrrole-based polymer (PDPP-TVT) film. The sequential aggregation is realized by introducing 1-bromonaphthalene additive into chloroform solvent. The structural evolution and assembly pathways of PDPP-TVT in initial solution and during printing were revealed using small-angle neutron scattering, cryogenic transmission electron microscopy, and time-resolved optical diagnostics. The results show that the poor interactions between PDPP-TVT side chains and BrN triggers side chain aggregation to form large H-aggregate nuclei in initial solution. The additive further selectively forces backbone aggregation on H-aggregate nuclei during printing with dynamics increasing from ca. 3 to >1000 s. Such prolonged growth window and selective growth of H-aggregates produce large fibers in printed film and therefore 3-fold increase in hole mobility. This work not only provides a promising route toward high-mobility printed conjugated polymer films but also reveals the important relationship between assembly pathways and film microstructure

Synthesis, Structure, and Superconductivity in the New-Structure-Type Compound: SrPt₆P₂

A metal-rich ternary phosphide, SrPt₆P₂, with a unique structure type was synthesized at high temperatures. Its crystal structure was determined by single-crystal X-ray diffraction [cubic space group <i>Pa</i>3̅; <i>Z</i> = 4; <i>a</i> = 8.474(2) Å, and <i>V</i> = 608.51(2) ų]. The structure features a unique three-dimensional anionic (Pt₆P₂)^2– network of vertex-shared Pt₆P trigonal prisms. The Sr atoms occupy a 12-coordinate (Pt) cage site and form a cubic close-packed (face-centered-cubic) arrangement, and the P atoms formally occupy tetrahedral interstices. The metallic compound becomes superconducting at 0.6 K, as evidenced by magnetic and resistivity measurements

Ligand-Stabilized Reduced-Dimensionality Perovskites

Metal halide perovskites have rapidly advanced thin-film photovoltaic performance; as a result, the materials’ observed instabilities urgently require a solution. Using density functional theory (DFT), we show that a low energy of formation, exacerbated in the presence of humidity, explains the propensity of perovskites to decompose back into their precursors. We find, also using DFT, that intercalation of phenyl­ethyl­ammonium between perovskite layers introduces quantitatively appreciable van der Waals interactions. These drive an increased formation energy and should therefore improve material stability. Here we report reduced-dimensionality (quasi-2D) perovskite films that exhibit improved stability while retaining the high performance of conventional three-dimensional perovskites. Continuous tuning of the dimensionality, as assessed using photo­physical studies, is achieved by the choice of stoichiometry in materials synthesis. We achieve the first certified hysteresis-free solar power conversion in a planar perovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity

Impact of Molecular Orientation and Spontaneous Interfacial Mixing on the Performance of Organic Solar Cells

A critically important question that must be answered to understand how organic solar cells operate and should be improved is how the orientation of the donor and acceptor molecules at the interface influences exciton diffusion, exciton dissociation by electron transfer, and recombination. It is exceedingly difficult to probe the orientation in bulk heterojunctions because there are many interfaces and they are arranged with varying angles with respect to the substrate. One of the best ways to study the interface is to make bilayer solar cells with just one donor–acceptor interface. Zinc phthalocyanine is particularly interesting to study because its orientation can be adjusted by using a 2 nm-thick copper iodide seed layer before it is deposited. Previous studies have claimed that solar cells in which fullerene acceptor molecules touch the face of zinc phthalocyanine have more current than ones in which the fullerenes touch the edge of zinc phthalocyanine because of suppressed recombination. We have more thoroughly characterized the system using in situ X-ray photoelectron spectroscopy and X-ray scattering and found that the interfaces are not as sharp as previous studies claimed when formed at room temperature or above. Fullerenes have a much stronger tendency to mix into the face-on films than into the edge-on films. Moreover we show that almost all of the increase in the current with face-on films can be attributed to improved exciton diffusion and to the formation of a spontaneously mixed interface, not suppressed recombination. This work highlights the importance of spontaneous interfacial molecular mixing in organic solar cells, the extent of which depends on molecular orientation of frontier molecules in donor domains