Two-dimensional Perovskitoids Enhance Stability in Perovskite Solar Cells.

Two-dimensional (2D)/three-dimensional (3D) perovskite heterostructures have played a key role in advancing the performance of perovskite solar cells (PSCs)1,2. However, the migration of cations between 2D and 3D layers results in the disruption of octahedral networks that leads to degradation in performance over time3,4. We hypothesized that perovskitoids, with robust organic-inorganic networks enabled by edge- and face-sharing, could impede ion migration. We explored a set of perovskitoids of varying dimensionality, and found that cation migration within perovskitoid/perovskite heterostructures was suppressed compared to the 2D/3D perovskite case. Increasing the dimensionality of perovskitoids improves charge transport when they are interfaced with 3D perovskite surfaces - this the result of enhanced octahedral connectivity and out-of-plane orientation. The 2D perovskitoid (A6BfP)8Pb7I22 (A6BfP: N-aminohexyl-benz[f]-phthalimide) provides efficient passivation of perovskite surfaces and enables uniform large-area perovskite films. Devices based on perovskitoid/perovskite heterostructures achieve a certified quasi-steady-state power conversion efficiency of 24.6% for centimeter-area PSCs. We removed the fragile hole transport layers and showed stable operation of the underlying perovskitoid/perovskite heterostructure at 85°C for 1,250 hours for encapsulated large-area devices in an air ambient.

Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites.

Perovskites with low ionic radii metal centres (for example, Ge perovskites) experience both geometrical constraints and a gain in electronic energy through distortion; for these reasons, synthetic attempts do not lead to octahedral [GeI6] perovskites, but rather, these crystallize into polar non-perovskite structures1-6. Here, inspired by the principles of supramolecular synthons7,8, we report the assembly of an organic scaffold within perovskite structures with the goal of influencing the geometric arrangement and electronic configuration of the crystal, resulting in the suppression of the lone pair expression of Ge and templating the symmetric octahedra. We find that, to produce extended homomeric non-covalent bonding, the organic motif needs to possess self-complementary properties implemented using distinct donor and acceptor sites. Compared with the non-perovskite structure, the resulting [GeI6]4- octahedra exhibit a direct bandgap with significant redshift (more than 0.5 eV, measured experimentally), 10 times lower octahedral distortion (inferred from measured single-crystal X-ray diffraction data) and 10 times higher electron and hole mobility (estimated by density functional theory). We show that the principle of this design is not limited to two-dimensional Ge perovskites; we implement it in the case of copper perovskite (also a low-radius metal centre), and we extend it to quasi-two-dimensional systems. We report photodiodes with Ge perovskites that outperform their non-octahedral and lead analogues. The construction of secondary sublattices that interlock with an inorganic framework within a crystal offers a new synthetic tool for templating hybrid lattices with controlled distortion and orbital arrangement, overcoming limitations in conventional perovskites.

Regulating surface potential maximizes voltage in all-perovskite tandems.

The open-circuit voltage (VOC) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs. 1,2). Quasi-Fermi-level-splitting measurements show VOC-limiting recombination at the electron-transport-layer contact3-5. This, we find, stems from inhomogeneous surface potential and poor perovskite-electron transport layer energetic alignment. Common monoammonium surface treatments fail to address this; as an alternative, we introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium, quasi-Fermi-level splitting increases by 90 meV, enabling 1.79 eV perovskite solar cells with a certified 1.33 V VOC and over 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record VOC of 2.19 V (89% of the detailed balance VOC limit) and over 27% PCE (26.3% certified quasi-steady state). These tandems retained more than 86% of their initial PCE after 500 h of operation.

Low-loss contacts on textured substrates for inverted perovskite solar cells.

Inverted perovskite solar cells (PSCs) promise enhanced operating stability compared to their normal-structure counterparts1-3. To improve efficiency further, it is crucial to combine effective light management with low interfacial losses4,5. Here we develop a conformal self-assembled monolayer (SAM) as the hole-selective contact on light-managing textured substrates. Molecular dynamics simulations indicate that cluster formation during phosphonic acid adsorption leads to incomplete SAM coverage. We devise a co-adsorbent strategy that disassembles high-order clusters, thus homogenizing the distribution of phosphonic acid molecules, and thereby minimizing interfacial recombination and improving electronic structures. We report a laboratory-measured power conversion efficiency (PCE) of 25.3% and a certified quasi-steady-state PCE of 24.8% for inverted PSCs, with a photocurrent approaching 95% of the Shockley-Queisser maximum. An encapsulated device having a PCE of 24.6% at room temperature retains 95% of its peak performance when stressed at 65 °C and 50% relative humidity following more than 1,000 h of maximum power point tracking under 1 sun illumination. This represents one of the most stable PSCs subjected to accelerated ageing: achieved with a PCE surpassing 24%. The engineering of phosphonic acid adsorption on textured substrates offers a promising avenue for efficient and stable PSCs. It is also anticipated to benefit other optoelectronic devices that require light management.

Suppressed phase segregation for triple-junction perovskite solar cells.

The tunable bandgaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics1,2. However, light-induced phase segregation limits their efficiency and stability3-5: this occurs in wide-bandgap (>1.65 electron volts) iodide/bromide mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that require a fully 2.0-electron-volt bandgap absorber2,6. Here we report that lattice distortion in iodide/bromide mixed perovskites is correlated with the suppression of phase segregation, generating an increased ion-migration energy barrier arising from the decreased average interatomic distance between the A-site cation and iodide. Using an approximately 2.0-electron-volt rubidium/caesium mixed-cation inorganic perovskite with large lattice distortion in the top subcell, we fabricated all-perovskite triple-junction solar cells and achieved an efficiency of 24.3 per cent (23.3 per cent certified quasi-steady-state efficiency) with an open-circuit voltage of 3.21 volts. This is, to our knowledge, the first reported certified efficiency for perovskite-based triple-junction solar cells. The triple-junction devices retain 80 per cent of their initial efficiency following 420 hours of operation at the maximum power point.

Constrained C2 adsorbate orientation enables CO-to-acetate electroreduction.

The carbon dioxide and carbon monoxide electroreduction reactions, when powered using low-carbon electricity, offer pathways to the decarbonization of chemical manufacture1,2. Copper (Cu) is relied on today for carbon-carbon coupling, in which it produces mixtures of more than ten C2+ chemicals3-6: a long-standing challenge lies in achieving selectivity to a single principal C2+ product7-9. Acetate is one such C2 compound on the path to the large but fossil-derived acetic acid market. Here we pursued dispersing a low concentration of Cu atoms in a host metal to favour the stabilization of ketenes10-chemical intermediates that are bound in monodentate fashion to the electrocatalyst. We synthesize Cu-in-Ag dilute (about 1 atomic per cent of Cu) alloy materials that we find to be highly selective for acetate electrosynthesis from CO at high *CO coverage, implemented at 10 atm pressure. Operando X-ray absorption spectroscopy indicates in situ-generated Cu clusters consisting of <4 atoms as active sites. We report a 12:1 ratio, an order of magnitude increase compared to the best previous reports, in the selectivity for acetate relative to all other products observed from the carbon monoxide electroreduction reaction. Combining catalyst design and reactor engineering, we achieve a CO-to-acetate Faradaic efficiency of 91% and report a Faradaic efficiency of 85% with an 820-h operating time. High selectivity benefits energy efficiency and downstream separation across all carbon-based electrochemical transformations, highlighting the importance of maximizing the Faradaic efficiency towards a single C2+ product11.

All-perovskite tandem solar cells with improved grain surface passivation.

All-perovskite tandem solar cells hold the promise of surpassing the efficiency limits of single-junction solar cells1-3; however, until now, the best-performing all-perovskite tandem solar cells have exhibited lower certified efficiency than have single-junction perovskite solar cells4,5. A thick mixed Pb-Sn narrow-bandgap subcell is needed to achieve high photocurrent density in tandem solar cells6, yet this is challenging owing to the short carrier diffusion length within Pb-Sn perovskites. Here we develop ammonium-cation-passivated Pb-Sn perovskites with long diffusion lengths, enabling subcells that have an absorber thickness of approximately 1.2 µm. Molecular dynamics simulations indicate that widely used phenethylammonium cations are only partially adsorbed on the surface defective sites at perovskite crystallization temperatures. The passivator adsorption is predicted to be enhanced using 4-trifluoromethyl-phenylammonium (CF3-PA), which exhibits a stronger perovskite surface-passivator interaction than does phenethylammonium. By adding a small amount of CF3-PA into the precursor solution, we increase the carrier diffusion length within Pb-Sn perovskites twofold, to over 5 µm, and increase the efficiency of Pb-Sn perovskite solar cells to over 22%. We report a certified efficiency of 26.4% in all-perovskite tandem solar cells, which exceeds that of the best-performing single-junction perovskite solar cells. Encapsulated tandem devices retain more than 90% of their initial performance after 600 h of operation at the maximum power point under 1 Sun illumination in ambient conditions.

Synthesis-on-substrate of quantum dot solids.

Perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency exceeding 20% have been achieved in both green and red wavelengths1-5; however, the performance of blue-emitting PeLEDs lags behind6,7. Ultrasmall CsPbBr3 quantum dots are promising candidates with which to realize efficient and stable blue PeLEDs, although it has proven challenging to synthesize a monodispersed population of ultrasmall CsPbBr3 quantum dots, and difficult to retain their solution-phase properties when casting into solid films8. Here we report the direct synthesis-on-substrate of films of suitably coupled, monodispersed, ultrasmall perovskite QDs. We develop ligand structures that enable control over the quantum dots' size, monodispersity and coupling during film-based synthesis. A head group (the side with higher electrostatic potential) on the ligand provides steric hindrance that suppresses the formation of layered perovskites. The tail (the side with lower electrostatic potential) is modified using halide substitution to increase the surface binding affinity, constraining resulting grains to sizes within the quantum confinement regime. The approach achieves high monodispersity (full-width at half-maximum = 23 nm with emission centred at 478 nm) united with strong coupling. We report as a result blue PeLEDs with an external quantum efficiency of 18% at 480 nm and 10% at 465 nm, to our knowledge the highest reported among perovskite blue LEDs by a factor of 1.5 and 2, respectively6,7.

Distribution control enables efficient reduced-dimensional perovskite LEDs.

Light-emitting diodes (LEDs) based on perovskite quantum dots have shown external quantum efficiencies (EQEs) of over 23% and narrowband emission, but suffer from limited operating stability1. Reduced-dimensional perovskites (RDPs) consisting of quantum wells (QWs) separated by organic intercalating cations show high exciton binding energies and have the potential to increase the stability and the photoluminescence quantum yield2,3. However, until now, RDP-based LEDs have exhibited lower EQEs and inferior colour purities4-6. We posit that the presence of variably confined QWs may contribute to non-radiative recombination losses and broadened emission. Here we report bright RDPs with a more monodispersed QW thickness distribution, achieved through the use of a bifunctional molecular additive that simultaneously controls the RDP polydispersity while passivating the perovskite QW surfaces. We synthesize a fluorinated triphenylphosphine oxide additive that hydrogen bonds with the organic cations, controlling their diffusion during RDP film deposition and suppressing the formation of low-thickness QWs. The phosphine oxide moiety passivates the perovskite grain boundaries via coordination bonding with unsaturated sites, which suppresses defect formation. This results in compact, smooth and uniform RDP thin films with narrowband emission and high photoluminescence quantum yield. This enables LEDs with an EQE of 25.6% with an average of 22.1 ±1.2% over 40 devices, and an operating half-life of two hours at an initial luminance of 7,200 candela per metre squared, indicating tenfold-enhanced operating stability relative to the best-known perovskite LEDs with an EQE exceeding 20%1,4-6.

CO2 Electrolyzers.

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Accelerated discovery of CO2 electrocatalysts using active machine learning.

The rapid increase in global energy demand and the need to replace carbon dioxide (CO2)-emitting fossil fuels with renewable sources have driven interest in chemical storage of intermittent solar and wind energy1,2. Particularly attractive is the electrochemical reduction of CO2 to chemical feedstocks, which uses both CO2 and renewable energy3-8. Copper has been the predominant electrocatalyst for this reaction when aiming for more valuable multi-carbon products9-16, and process improvements have been particularly notable when targeting ethylene. However, the energy efficiency and productivity (current density) achieved so far still fall below the values required to produce ethylene at cost-competitive prices. Here we describe Cu-Al electrocatalysts, identified using density functional theory calculations in combination with active machine learning, that efficiently reduce CO2 to ethylene with the highest Faradaic efficiency reported so far. This Faradaic efficiency of over 80 per cent (compared to about 66 per cent for pure Cu) is achieved at a current density of 400 milliamperes per square centimetre (at 1.5 volts versus a reversible hydrogen electrode) and a cathodic-side (half-cell) ethylene power conversion efficiency of 55 ± 2 per cent at 150 milliamperes per square centimetre. We perform computational studies that suggest that the Cu-Al alloys provide multiple sites and surface orientations with near-optimal CO binding for both efficient and selective CO2 reduction17. Furthermore, in situ X-ray absorption measurements reveal that Cu and Al enable a favourable Cu coordination environment that enhances C-C dimerization. These findings illustrate the value of computation and machine learning in guiding the experimental exploration of multi-metallic systems that go beyond the limitations of conventional single-metal electrocatalysts.

Molecular tuning of CO2-to-ethylene conversion.

The electrocatalytic reduction of carbon dioxide, powered by renewable electricity, to produce valuable fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of energy produced by intermittent renewable sources1. However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO2RR) remains a challenge2. Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity3-5, and this has recently been explored for the reaction on copper by controlling morphology6, grain boundaries7, facets8, oxidation state9 and dopants10. Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 milliamperes per square centimetre in the best catalyst reported so far9), resulting in a low energy efficiency. Here we present a molecular tuning strategy-the functionalization of the surface of electrocatalysts with organic molecules-that stabilizes intermediates for more selective CO2RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived by electro-dimerization of arylpyridiniums11, adsorbed on copper. We find that the adhered molecules improve the stabilization of an 'atop-bound' CO intermediate (that is, an intermediate bound to a single copper atom), thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO2RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 milliamperes per square centimetre in a liquid-electrolyte flow cell in a neutral medium. We report stable ethylene electrosynthesis for 190 hours in a system based on a membrane-electrode assembly that provides a full-cell energy efficiency of 20 per cent. We anticipate that this may be generalized to enable molecular strategies to complement heterogeneous catalysts by stabilizing intermediates through local molecular tuning.

Molecular surface programming of rectifying junctions between InAs colloidal quantum dot solids.

Heavy-metal-free III-V colloidal quantum dots (CQDs) show promise in optoelectronics: Recent advancements in the synthesis of large-diameter indium arsenide (InAs) CQDs provide access to short-wave infrared (IR) wavelengths for three-dimensional ranging and imaging. In early studies, however, we were unable to achieve a rectifying photodiode using CQDs and molybdenum oxide/polymer hole transport layers, as the shallow valence bandedge (5.0 eV) was misaligned with the ionization potentials of the widely used transport layers. This occurred when increasing CQD diameter to decrease the bandgap below 1.1 eV. Here, we develop a rectifying junction among InAs CQD layers, where we use molecular surface modifiers to tune the energy levels of InAs CQDs electrostatically. Previously developed bifunctional dithiol ligands, established for II-VI and IV-VI CQDs, exhibit slow reaction kinetics with III-V surfaces, causing the exchange to fail. We study carboxylate and thiolate binding groups, united with electron-donating free end groups, that shift upward the valence bandedge of InAs CQDs, producing valence band energies as shallow as 4.8 eV. Photophysical studies combined with density functional theory show that carboxylate-based passivants participate in strong bidentate bridging with both In and As on the CQD surface. The tuned CQD layer incorporated into a photodiode structure achieves improved performance with EQE (external quantum efficiency) of 35% (>1 µm) and dark current density < 400 nA cm-2, a >25% increase in EQE and >90% reduced dark current density compared to the reference device. This work represents an advance over previous III-V CQD short-wavelength IR photodetectors (EQE < 5%, dark current > 10,000 nA cm-2).

Lattice anchoring stabilizes solution-processed semiconductors.

The stability of solution-processed semiconductors remains an important area for improvement on their path to wider deployment. Inorganic caesium lead halide perovskites have a bandgap well suited to tandem solar cells1 but suffer from an undesired phase transition near room temperature2. Colloidal quantum dots (CQDs) are structurally robust materials prized for their size-tunable bandgap3; however, they also require further advances in stability because they are prone to aggregation and surface oxidization at high temperatures as a consequence of incomplete surface passivation4,5. Here we report 'lattice-anchored' hybrid materials that combine caesium lead halide perovskites with lead chalcogenide CQDs, in which lattice matching between the two materials contributes to a stability exceeding that of the constituents. We find that CQDs keep the perovskite in its desired cubic phase, suppressing the transition to the undesired lattice-mismatched phases. The stability of the CQD-anchored perovskite in air is enhanced by an order of magnitude compared with pristine perovskite, and the material remains stable for more than six months at ambient conditions (25 degrees Celsius and about 30 per cent humidity) and more than five hours at 200 degrees Celsius. The perovskite prevents oxidation of the CQD surfaces and reduces the agglomeration of the nanoparticles at 100 degrees Celsius by a factor of five compared with CQD controls. The matrix-protected CQDs show a photoluminescence quantum efficiency of 30 per cent for a CQD solid emitting at infrared wavelengths. The lattice-anchored CQD:perovskite solid exhibits a doubling in charge carrier mobility as a result of a reduced energy barrier for carrier hopping compared with the pure CQD solid. These benefits have potential uses in solution-processed optoelectronic devices.

Bimetallic Metal Sites in Metal-Organic Frameworks Facilitate the Production of 1-Butene from Electrosynthesized Ethylene.

Converting CO2 to synthetic hydrocarbon fuels is of increasing interest. In light of progress in electrified CO2 to ethylene, we explored routes to dimerize to 1-butene, an olefin that can serve as a building block to ethylene longer-chain alkanes. With goal of selective and active dimerization, we investigate a series of metal-organic frameworks having bimetallic catalytic sites. We find that the tunable pore structure enables optimization of selectivity and that periodic pore channels enhance activity. In a tandem system for the conversion of CO2 to 1-C4H8, wherein the outlet cathodic gas from a CO2-to-C2H4 electrolyzer is fed directly (via a dehumidification stage) into the C2H4 dimerizer, we study the highest-performing MOF found herein: M' = Ru and M″ = Ni in the bimetallic two-dimensional M'2(OAc)4M″(CN)4 MOF. We report a 1-C4H8 production rate of 1.3 mol gcat-1 h-1 and a C2H4 conversion of 97%. From these experimental data, we project an estimated cradle-to-gate carbon intensity of -2.1 kg-CO2e/kg-1-C4H8 when CO2 is supplied from direct air capture and when the required energy is supplied by electricity having the carbon intensity of wind.

Pourbaix Machine Learning Framework Identifies Acidic Water Oxidation Catalysts Exhibiting Suppressed Ruthenium Dissolution.

The demand for green hydrogen has raised concerns over the availability of iridium used in oxygen evolution reaction catalysts. We identify catalysts with the aid of a machine learning-aided computational pipeline trained on more than 36,000 mixed metal oxides. The pipeline accurately predicts Pourbaix decomposition energy (Gpbx) from unrelaxed structures with a mean absolute error of 77 meV per atom, enabling us to screen 2070 new metallic oxides with respect to their prospective stability under acidic conditions. The search identifies Ru0.6Cr0.2Ti0.2O2 as a candidate having the promise of increased durability: experimentally, we find that it provides an overpotential of 267 mV at 100 mA cm-2 and that it operates at this current density for over 200 h and exhibits a rate of overpotential increase of 25 µV h-1. Surface density functional theory calculations reveal that Ti increases metal-oxygen covalency, a potential route to increased stability, while Cr lowers the energy barrier of the HOO* formation rate-determining step, increasing activity compared to RuO2 and reducing overpotential by 40 mV at 100 mA cm-2 while maintaining stability. In situ X-ray absorption spectroscopy and ex situ ptychography-scanning transmission X-ray microscopy show the evolution of a metastable structure during the reaction, slowing Ru mass dissolution by 20× and suppressing lattice oxygen participation by >60% compared to RuO2.

Selective Electrified Propylene-to-Propylene Glycol Oxidation on Activated Rh-Doped Pd.

Renewable-energy-powered electrosynthesis has the potential to contribute to decarbonizing the production of propylene glycol, a chemical that is used currently in the manufacture of polyesters and antifreeze and has a high carbon intensity. Unfortunately, to date, the electrooxidation of propylene under ambient conditions has suffered from a wide product distribution, leading to a low faradic efficiency toward the desired propylene glycol. We undertook mechanistic investigations and found that the reconstruction of Pd to PdO occurs, followed by hydroxide formation under anodic bias. The formation of this metastable hydroxide layer arrests the progressive dissolution of Pd in a locally acidic environment, increases the activity, and steers the reaction pathway toward propylene glycol. Rh-doped Pd further improves propylene glycol selectivity. Density functional theory (DFT) suggests that the Rh dopant lowers the energy associated with the production of the final intermediate in propylene glycol formation and renders the desorption step spontaneous, a concept consistent with experimental studies. We report a 75% faradic efficiency toward propylene glycol maintained over 100 h of operation.

Nickel Oxide Hole Injection Layers for Balanced Charge Injection in Quantum Dot Light-Emitting Diodes.

Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation displays, but suffer from carrier imbalance arising from lower hole injection compared to electron injection. A defect engineering strategy is reported to tackle transport limitations in nickel oxide-based inorganic hole-injection layers (HILs) and find that hole injection is able to enhance in high-performance InP QLEDs using the newly designed material. Through optoelectronic simulations, how the electronic properties of NiOx affect hole injection efficiency into an InP QD layer, finding that efficient hole injection depends on lowering the hole injection barrier and enhancing the acceptor density of NiOx is explored. Li doping and oxygen enriching are identified as effective strategies to control intrinsic and extrinsic defects in NiOx, thereby increasing acceptor density, as evidenced by density functional theory calculations and experimental validation. With fine-tuned inorganic HIL, InP QLEDs exhibit a luminance of 45 200 cd m-2 and an external quantum efficiency of 19.9%, surpassing previous inorganic HIL-based QLEDs. This study provides a path to designing inorganic materials for more efficient and sustainable lighting and display technologies.

Anion optimization for bifunctional surface passivation in perovskite solar cells.

Pseudo-halide (PH) anion engineering has emerged as a surface passivation strategy of interest for perovskite-based optoelectronics; but until now, PH anions have led to insufficient defect passivation and thus to undesired deep impurity states. The size of the chemical space of PH anions (>106 molecules) has so far limited attempts to explore the full family of candidate molecules. We created a machine learning workflow to speed up the discovery process using full-density functional theory calculations for training the model. The physics-informed machine learning model allowed us to pinpoint promising molecules with a head group that prevents lattice distortion and anti-site defect formation, and a tail group optimized for strong attachment to the surface. We identified 15 potential bifunctional PH anions with the ability to passivate both donors and acceptors, and through experimentation, discovered that sodium thioglycolate was the most effective passivant. This strategy resulted in a power-conversion efficiency of 24.56% with a high open-circuit voltage of 1.19 volts (24.04% National Renewable Energy Lab-certified quasi-steady-state) in inverted perovskite solar cells. Encapsulated devices maintained 96% of their initial power-conversion energy during 900 hours of one-sun operation at the maximum power point.

Organic Polar Crystals, Second Harmonic Generation, and Piezoelectric Effects from Heteroadamantanes in the Space Group R3m.

Polar crystalline materials, a subset of the non-centrosymmetric materials, are highly sought after. Their symmetry properties make them pyroelectric and also piezoelectric and capable of second-harmonic generation (SHG). For SHG and piezoelectric applications, metal oxides are commonly used. The advantages of oxides are durability and hardness - downsides are the need for high-temperature synthesis/processing and often the need to include toxic metals. Organic polar crystals, on the other hand, can avoid toxic metals and can be amenable to solution-state processing. While the vast majority of polar organic molecules crystallize in non-polar space groups, we found that both 7-chloro-1,3,5-triazaadamantane, for short Cl-TAA, and also the related Br-TAA (but not I-TAA) form polar crystals in the space group R3m, easily obtained from dichloromethane solution. Measurements confirm piezoelectric and SHG properties for Cl-TAA and Br-TAA. When the two species are crystallized together, solid solutions form, suggesting that properties of future materials can be tuned continuously.