The use of 2D perovskite capping layers to passivate the surface defects of 3D perovskite active layers has become ubiquitous in high performance lead halide perovskite solar cells. However, these 2D/3D interfaces can be highly dynamic, with the structure evolving to form various mixed dimensional phases when exposed to thermal stress or illumination. Changes in the photoluminescence spectrum of formamidinium lead iodide (FAPbI3) films capped with alkylammonium-based 2D perovskites as they age at 100 °C or under simulated 1 sun illumination indicate that the 2D perovskite transforms to progressively larger inorganic layer thicknesses (denoted by layer number n), eventually approaching a steady-state condition where only the 3D perovskite (n = ∞) is detectable. We find that this transformation slows by a factor of ∼2 when the length of the alkyl chain in the organic monoammonium ligand is increased from butylammonium to dodecylammonium. Furthermore, replacing dodecylammonium with its diammonium ligand counterpart, 1,12-dodecanediammonium, slows the structural transformation by 10-fold. These results point to the use of diammonium ligands as a possible pathway to form stable 2D/3D interfaces.

Despite the rapid rise in perovskite solar cell efficiency, poor reproducibility remains a major barrier to commercialization. Film crystallization and device performance are highly sensitive to environmental factors during fabrication, yet their complex interactions are not well understood. In this work, we present a systematic framework to investigate the influence of both individual and coupled environmental variables on device efficiency and crystallization kinetics. We developed an integrated fabrication platform with precise, independent control over ambient solvent partial pressure, absolute humidity, and temperature during spin-coating and thermal-annealing processes, respectively. Using the platform, we implemented a closed-loop Bayesian optimization framework to efficiently explore the multi-dimensional processing space. We mapped the impact of these environmental variables on device performance and identified coupled effects among them. In-situ grazing-incidence wide-angle X-ray scattering measurements further validated these findings by revealing a nonlinear interaction between absolute humidity and solvent partial pressure during spin-coating, which affects crystallization dynamics. To isolate and quantify these interactions, we developed an interpretable machine learning approach that combines knowledge distillation with Shapley interaction analysis. The model revealed the contribution of each interaction varies across different processing conditions. Our study highlights the importance of integrated ambient sensing and control to achieve repeatable perovskite solar cells, and demonstrates the utility of combining active learning with interpretable machine learning to navigate complex, high-dimensional processing landscapes.

Two-dimensional (2D) hybrid organic-inorganic perovskites are potentially promising materials as passivation layers that can enhance the efficiency and stability of perovskite photovoltaics. The ability to suppress ion transport has been proposed as a stabilization mechanism, yet effective characterization of relevant modes of halide diffusion in 2D perovskites is nascent. In light of this knowledge gap, we combine molecular dynamics simulations with enhanced sampling and experimental validation to systematically characterize how ligand chemistry in seven (R-NH3)2PbI4 systems impacts halide diffusion, particularly in the out-of-plane direction. We find that increasing stiffness and length of ligands generally inhibits ion transport, while increasing ligand polarization generally enhances it. Structural and energetic analyses of the migration pathways provide quantitative explanations for these trends, which reflect aspects of the disorder of the organic layer. Overall, this mechanistic analysis greatly enhances the current understanding of halide migration in 2D hybrid organic-inorganic perovskites and yields insights that can inform the design of future passivation materials.

Interest in organic small molecules that exhibit second-scale phosphorescence at room temperature has grown immensely in recent years due to their potential applications in sensing, anticounterfeiting, and bioimaging. However, such material systems are rare—requiring second-scale triplet lifetimes, efficient intersystem crossing, and slow rates of nonradiative recombination. This third requirement has been met by isolating phosphors in a rigid matrix, or by aggregating them into densely packed crystals or powders to suppress the molecular vibrations that lead to recombination. While these techniques work well for a small subset of molecules with specific properties, most isolated molecules in a rigid matrix do not phosphoresce, and most macroscopic aggregates experience significant triplet quenching. In this work, we find a middle ground between these extremes by forming microscopic [approximately submicron sized] phosphor aggregates in rigid polymer matrices using a simple drop casting and thermal annealing process. Using this technique, we activate second-scale phosphorescence at room temperature in 20 molecules that do not otherwise phosphoresce using conventional matrix-isolation or crystallization approaches. We find that increased chromophore loading increases aggregate sizes. Excitons are thus able to diffuse further and interact more, and triplet-triplet annihilation dominates. Furthermore, we determine that excimer formation in some aggregates leads to increased rates of triplet generation—complementing the effect of nonradiative recombination suppression and further enhancing phosphorescence. In sum, the simplicity and robustness of this blending approach significantly loosens the design constraints to access second-scale emission with organic phosphors, allowing researchers to choose from a broader catalog of organic materials to match the desired properties for a given application.

2D hybrid organic-inorganic perovskites are potentially promising materials as passivation layers that can enhance the efficiency and stability of perovskite photovoltaics. The ability to suppress ion transport is proposed as a stabilization mechanism, yet an effective characterization of relevant modes of halide diffusion in 2D perovskites is nascent. In light of this knowledge gap, molecular dynamics simulations with enhanced sampling and experimental validation to systematically characterize how ligand chemistry in seven (R-NH3)2PbI4 systems impacts halide diffusion, particularly in the out-of-plane direction is combined. It is found that increasing stiffness and length of ligands generally inhibits ion transport, while increasing ligand polarization generally enhances it. Structural and energetic analyses of the migration pathways provide quantitative explanations for these trends, which reflect aspects of the disorder of the organic layer. Overall, this mechanistic analysis greatly enhances the current understanding of halide migration in 2D hybrid organic-inorganic perovskites and yields insights that can inform the design of future passivation materials. This study leverages molecular dynamics simulation and experimental characterization to elucidate the effects of ligand chemistry on suppressing ion transport in 2D hybrid-inorganic perovskites. Analyses reveal that increasing stiffness and length of ligands generally inhibits ion transport, while increasing ligand polarization generally enhances it. These insights provide possible principles for designing passivation materials to enhance the stability of perovskite photovoltaics. image

Organic small molecules that exhibit second-scale phosphorescence at room temperature are of interest for potential applications in sensing, anticounterfeiting, and bioimaging. However, such materials systems are uncommon-requiring millisecond to second-scale triplet lifetimes, efficient intersystem crossing, and slow rates of nonradiative recombination. Here, a simple and scalable approach is demonstrated to activate long-lived phosphorescence in a wide variety of molecules by suspending them in rigid polymer hosts and annealing them above the polymer's glass transition temperature. This process produces submicron aggregates of the chromophore, which suppresses intramolecular motion that leads to nonradiative recombination and minimizes triplet-triplet annihilation that quenches phosphorescence in larger aggregates. In some cases, evidence of excimer-mediated intersystem crossing that enhances triplet generation in aggregated chromophores is found. In short, this approach circumvents the current design rules for long-lived phosphors, which will streamline their discovery and development.

2D Ruddlesden-Popper metal-halide perovskites exhibit structural diversity due to a variety of choices of organic ligands. Incorporating bifunctional ligands in such materials is particularly intriguing since it can result in novel electronic properties and functions. However, an in-depth understanding of the effects of bifunctional ligands on perovskite structures and, consequently, their electronic and excitonic properties, is still lacking. Here, n = 1 2D perovskites built with organic ligands containing CN, OH, COOH, phenyl (Ph), and CH3 functional groups are investigated using ultraviolet and inverse photoemission spectroscopies, density functional theory calculations, and tight-binding model analyses. The experimentally determined electronic gaps of the CN, COOH, Ph, and CH3 based perovskites exhibit a strong correlation with the in-plane PbIPb bond angle, while the OH based perovskite deviates from the linear trend. Based on the band structure calculations, this anomaly is attributed to the out-of-plane dispersion, caused predominantly by significant interlayer electronic coupling that is present in OH based perovskites. These results highlight the complex and diverse impacts of organic ligands on electronic properties, especially in terms of the involvement of strong interlayer electronic coupling. The impact of the bifunctional ligands on the evolution of the exciton binding energy is also addressed. This study explores the impact of bifunctional ligands on optoelectronic properties of 2D perovskites. A strong correlation between electronic gap and PbIPb bond angle is observed for CN, COOH, Ph, and CH3 based perovskites. The unique and different behavior of the OH based compound is attributed to strong interlayer electronic coupling, highlighting the complex role of ligands on 2D perovskites.image

Voltage-dependent characterizations of organic solar cells with brightly-emitting charge-transfer excitons reveal excitation dynamics and trends as a function of donor molecule.

Organic semiconductors (OSCs) have attracted rapidly growing interest given their potential to create innovative optoelectronic applications. One major drawback is the sensitivity of the electrical properties to the presence of impurities in the OSC film: even small traces can significantly alter the properties of the OSC layer by introducing electronic trapping states, leading to efficiency losses and degraded charge carrier mobility. Since impurities can be introduced at many stages of device fabrication, from synthetic impurities to process solvents to the lining on syringes used to deposit solutions, identifying device structures that are more tolerant of their presence is necessary. Here, we employ a data-driven device design, wherein simulations are combined with experiment to reveal organic field-effect transistor (OFET) geometries that enable the use of lower standards of semiconductor purity without impacting the performance. The phenomenon is attributed to how the filling of trap states is modulated by the gate potential. Guided by the simulation results, we were able to recover the performance of a pure device in OFETs with optimal geometry containing 2% known impurity. These results provide a pathway for developing high-performance organic devices at a lower cost by adopting a device architecture that is more tolerant of defects..

Incorporating crystalline organic semiconductors into electronic devices requires understanding of heteroepitaxy given the ubiquity of heterojunctions in these devices. However, while rules for commensurate epitaxy of covalent or ionic inorganic material systems are known to be dictated by lattice matching constraints, rules for heteroepitaxy of molecular systems are still being written. Here, it is found that lattice matching alone is insufficient to achieve heteroepitaxy in molecular systems, owing to weak intermolecular forces that describe molecular crystals. It is found that, in addition, the lattice matched plane also must be the lowest energy surface of the adcrystal to achieve one-to-one commensurate molecular heteroepitaxy over a large area. Ultraviolet photoelectron spectroscopy demonstrates the lattice matched interface to be of higher electronic quality than a disordered interface of the same materials.

Transparent photovoltaics (TPVs) can be integrated into the surfaces of buildings and vehicles to provide point‐of‐use power without impacting aesthetics. Unlike TPVs that target the photon‐rich near‐infrared portion of the solar spectrum, TPVs that harvest ultraviolet (UV) photons can have significantly higher transparency and color neutrality, offering a superior solution for low‐power electronics with stringent aesthetic tolerance. In addition to being highly transparent and colorless, an ideal UV‐absorbing TPV should also be operationally stable and scalable over large areas while still outputting sufficient power for its specified application. None of today's TPVs meet all these criteria simultaneously. Here, the first UV‐absorbing TPV is demonstrated that satisfies all four criteria by using CsPbCl 2.5 Br 0.5 as the absorber. By precisely tuning the halide ratio during thermal co‐evaporation, high‐quality large‐area perovskite films can be accessed with an ideal absorption cutoff for aesthetic performance. The resulting TPVs exhibit a record average visible transmittance of 84.6% and a color rendering index of 96.5, while maintaining an output power density of 11 W m −2 under one‐sun illumination. Further, the large‐area prototypes up to 25 cm 2 are demonstrated, that are operationally stable with extrapolated lifetimes of >20 yrs under outdoor conditions.

Metal halide perovskites are versatile materials whichhave alreadydemonstrated exceptional performance in diverse optoelectronic devices.The progress has been significant; however, the fundamental understandingof the physics of charge injection remains elusive, impeding furtheradvancements. Here, we use field-effect transistors (FETs) to investigatethe impact of surface functionalization on the charge injection andtransport in thin films of phenethylammonium tin iodide (PEA(2)SnI(4)). We show that self-assembled monolayers (SAMs) canboth assist in reducing the Schottky barrier and act as an ion blockinglayer between the contact and the perovskite film, limiting interfacialchemical reactions. Consequently, the contact resistance is loweredby more than 3 times compared to untreated contacts. The temperaturedependence of the charge carrier mobility is discussed consideringthe contributions from the channel and contacts, respectively. Ourresults provide a quantitative framework for the charge injectionin metal halide perovskites and will contribute toward the progressof high-performance optoelectronic devices including solar cells,light-emitting diodes, as well as X-ray and photodetectors.

As the stability of organic and perovskite solar cells improves, accelerated ageing methods become increasingly essential to elucidate their long-term degradation mechanisms and to predict their real-world operational lifetimes. By effectively applying these underutilized tests, emerging photovoltaic technologies can be de-risked and their time to market can be expedited.

Contortedpolycyclic aromatic molecules, such as corannulenes andsumanenes, have been studied as host molecules for fullerenes dueto their complementary geometries. It has been suggested that strongerassociations with fullerenes can be attained by extending their & pi;surface or by incorporating heteroatoms, as unsubstituted corannuleneand sumanene do not readily complex with fullerenes in solution. Here,we design and synthesize & pi;-extended buckybowls derived fromcontorted hexabenzocoronene and pentabenzocoronene with either pentylor butoxy side chains. These coronene-based buckybowls have approximatelytwice the & pi; surface compared to unsubstituted corannulene andsumanene. Buckybowls with pentyl side chains complex with C-60 in a preferred 1:1 buckybowl-to-C-60 stoichiometry, withassociation constants on the order of 10(3) M-1. Complexation with C-60 further strengthens with the additionof heteroatoms in buckybowls bearing butoxy side chains. We find apreferred 1:2 association stoichiometry with fullerene and associationconstants on the order of 10(4) M-1. Densityfunctional theory calculations suggest the larger dipole moment onthe butoxy-substituted buckybowls relative to their pentyl-substitutedcounterparts is responsible. This greater dipole moment polarizesC(60), leading to a preferred 1:2 stoichiometry and largerassociation constants in the complexation of buckybowls with butoxyside chains and C-60.

Perovskite CsPbI3 is a promising photovoltaic absorber material, thanks to its ideal bandgap for Si-tandem solar cell applications and its excellent thermochemical stability compared with hybrid organic–inorganic perovskites. However, CsPbI3 has its own stability challenges as its photoactive β- and γ-polymorphs are thermodynamically unstable at room temperature compared with the yellow non-perovskite δ-phase. Stabilizing CsPbI3 has, thus, been the subject of considerable research in recent years. While some approaches, such as alloying with halides and reducing crystalline domain size, have proven effective in improving phase stability, these benefits have, thus far, come at the expense of photovoltaic efficiency compared with the state-of-the-art CsPbI3 solar cells. In this perspective, we discuss the progress and limitations of inorganic perovskite stabilization techniques and look forward at how to achieve inorganic perovskite solar cells with both commercially viable efficiencies and lifetimes.

Organic photovoltaic cells that employ Y-series non-fullerene acceptors (NFAs) have recently achieved impressive power-conversion efficiencies (>18%). To fulfill their commercial promise, it is important to quantify their operational lifetimes and understand their degradation mechanisms. In this work, the spectral-dependent photostability of films and solar cells comprising several Y-series acceptors and the donor polymer PM6 is investigated systematically. By applying longpass filters during aging, it is shown that UV/near-UV photons are responsible for the photochemical decomposition of Y-series acceptors; this degradation is the primary driver of early solar cell performance losses. Using mass spectrometry, the vinylene linkage between the core and electron-accepting moieties of Y-series acceptors is identified as the weak point susceptible to cleavage under UV-illumination. Employing a series of device characterization, along with numerical simulations, the efficiency losses in organic photovoltaic cells are attributed to the formation of traps, which reduces charge extraction efficiency and facilitates non-radiative recombination as the Y-series acceptors degrade. This study provides new insights for molecular degradation of organic photovoltaic absorber materials and highlights the importance of future molecular design and strategies for improved solar cell stability.

High-performance inorganic-organic lead halide perovskite solar cells (PSCs) are often fabricated with a liquid additive such as dimethyl sulfoxide (DMSO) which retards crystallization and reduces roughness and pinholes in the perovskite layers. However, DMSO can be trapped during perovskite film formation and induce voids and undesired reaction byproducts upon later processing steps. Here, we show that we can reduce the amount of residual DMSO in as-spin-coated films significantly - by 30 times - through use of pre-heated substrates, or a so-called hot-casting method. Hot-casting increases the perovskite film thickness which allows us to reduce the perovskite solution concentration. By reducing the amount of DMSO in proportion to the concentration of perovskite precursors and using hot-casting, we are able to fabricate perovskite layers with improved perovskite-substrate buried interfaces by suppressing the formation of byproducts which increase trap density and accelerate degradation of the perovskite layers. The best-performing PSCs exhibit power conversion efficiency (PCE) of 23.4% (23.0% stabilized efficiency) under simulated solar illumination. Furthermore, encapsulated devices showed considerably reduced post-burn-in decay of -0.84% of initial efficiency per 100 h, retaining more than 80% and 93% of their initial and post-burn-in efficiencies after 800 h of operation with maximum power point tracking (MPPT) under high-power of ultraviolet-(UV-)containing continuous light exposure (overall power density of 1.1 sun with 2.6 times higher UV-region power density than AM 1.5G).

All-inorganic beta-CsPbI3 has superior chemical and thermal stability compared to its hybrid counterparts, but the stability of state-of-the-art beta-CsPbI3 perovskite solar cells (PSCs) under normal operating conditions (i.e., under illumination in an inert atmosphere) remains inferior to their hybrid counterparts. Here, we found that the lattice distortion in CsPbI3 near the perovskite/electron transport layer (ETL) interface can induce polymorphic transformation in encapsulated CsPbI3 films aged under illumination. To suppress this lattice distortion, we introduced alkyltrimethoxysilane strain-release layers (SRLs) at the perovskite/ETL interface. We found the SRL with the longest alkyl chain is the most effective at reducing interfacial lattice distortion, leading to enhanced charge transfer at the perovskite/ETL interface and improved phase/device stability. Its incorporation in beta-CsPbI3 solar cells resulted in a power-conversion efficiency of 20.1% and an operational lifetime with an extrapolated T(80 )of > 3000 h for encapsulated devices tested under continuous illumination under maximum power point tracking conditions.

The rapid development of organic electrochemical transistor (OECTs)-based circuits brings new opportunities for next-generation integrated bioelectronics. The all-polymer bulk-heterojunction (BHJ) offers an attractive, inexpensive alternative to achieve efficient ambipolar OECTs, and building blocks of logic circuits constructed from them, but have not been investigated to date. Here, the first all-polymer BHJ-based OECTs are reported, consisting of a blend of new p-type ladder conjugated polymer and a state-of-the-art n-type ladder polymer. The whole ladder-type polymer BHJ also proves that side chains are not necessary for good ion transport. Instead, the polymer nanostructures play a critical role in the ion penetration and transportation and thus in the device performance. It also provides a facile strategy and simplifies the fabrication process, forgoing the need to pattern multiple active layers. In addition, the development of complementary metal-oxide-semiconductor (CMOS)-like OECTs allows the pursuit of advanced functional logic circuitry, including inverters and NAND gates, as well as for amplifying electrophysiology signals. This work opens a new approach to the design of new materials for OECTs and will contribute to the development of organic heterojunctions for ambipolar OECTs toward high-performing logic circuits.

The ongoing effort toward stabilizing hybrid perovskite solar cells and enhancing their performance has stimulated the community to pursue a number of strategies. Over the recent years, these efforts have focused on perovskite materials design, which increasingly relies on molecular modulators that engage in halogen bonding, a uniquely directional noncovalent (supramolecular) interaction. Halogen bonding in hybrid perovskites is reported to drive perovskite assembly, increase its stability against moisture and ion migration, passivate defects, and tune interfacial energetics. The resulting perovskites are shown to exhibit superior mechanical properties, and devices incorporating these materials have seen drastic improvements in their performance, all of which have been ascribed to halogen bonding. While most of these developments have so far relied on the incorporation of off-the-shelf molecular modulators that interact with the perovskite surface to effect interfacial properties, further advancements will require careful consideration of the nature of halogen bonding and rigorous structural assessments in order to aid development of next-generation materials. Here, we provide a critical overview of the recent developments in the use of halogen bonding agents in hybrid perovskite photovoltaics with a perspective on their utility in the future.