Maral Vafaie

Direct synthesis of C₃₊ hydrocarbons via the electrochemical CO₂ reduction reaction is highly desirable for producing sustainable chemicals. However, this approach remains challenging due to the limited ability of current electrocatalysts to adsorb and couple key reaction intermediates effectively, with promising systems, such as Ni oxyhydroxide-derived catalysts, still exhibiting partial current densities toward C₃₊ hydrocarbons -2. Motivated by the limited activity and control over the active site environment of these systems, we hypothesize that reducing the size of metallic Ni modifies its electronic states and introduces interfacial metal-support sites that promote more balanced *CO adsorption, critical for facilitating C-C coupling beyond C₂ intermediates. Here, we report a plasma-assisted deposition method to synthesize size-controlled metallic Ni nanoislands on a carbon support. Characterization revealed that reducing the nanoisland size (20-fold enhancement in the Ni-mass-based activity versus state-of-the-art catalysts.

Lead‐free III‐V colloidal quantum dots (CQDs) are of significant interest for their potential in near‐infrared (NIR) to short‐wave infrared (SWIR) photodetection. However, achieving effective surface passivation remains challenging, especially as larger CQD sizes introduce more complex surface facets and compositions while shifting the absorption peak from the NIR to the SWIR range. In this study, a mixed‐halide passivation strategy is developed for large InAs CQDs, an approach that led to a doubling in anti‐oxidation ability and achieves a hole mobility of 0.03 cm² Vs⁻¹. These in turn led to a T90 lifetime of 50 h and enhanced operating stability in photodetectors operating at 1140 nm. Density functional theory (DFT) simulations and facet characterization indicate that exposed facets and edges are well passivated using a mixture of indium halides, which provide a stronger desorption energy compared to single‐halide passivation. This approach yields photodetectors with an external quantum efficiency (EQE) of 75% and a response time of 10 ns, an advance for InAs photodetectors operating at 1140 nm.

The quantum-dot-in-perovskite matrix (DIM) is an emerging class of semiconductors for optoelectronics enabled by their complementary charge transport properties and stability improvements. However, a detailed understanding of the pure electrical properties in DIM is still in its early stage. Here, we developed PbS quantum dot-in-CsSnI₃ matrix solids exhibiting improved electrical properties and enhanced stability. PbS incorporation reduces the tensile strain of DIM films compared to that of pristine CsSnI₃, consequently increasing the electrical conductivity. Electrical conductivity is tunable between 20 and 130 S/cm as a function of PbS concentration. Notably, a decoupling of electrical conductivity and Seebeck coefficient is observed upon PbS addition into the perovskite matrix, which is attractive for thermoelectric applications. Density functional theory analysis reveals that at low concentrations of PbS, light holes/electrons govern the overall transport properties in DIM, while heavy holes/electrons begin to dominate as the PbS concentration increases. Understanding the electrical properties would help for designing DIMs with specific properties for various technological applications.

The synthesis of highly monodispersed InAs colloidal quantum dots (CQDs) is needed in InAs CQD-based optoelectronic devices. Because of the complexities of working with arsenic precursors such as tris-trimethylsilyl arsine ((TMSi)₃As) and tris-trimethylgermyl arsine ((TMGe)₃As), several attempts have been made to identify new candidates for synthesis; yet, to date, only the aforementioned two highly reactive precursors have led to excellent photodetector device performance. We begin the present study by investigating the mechanism, finding that the use of the cosurfactant dioctylamine plays a crucial role in producing monodispersed InAs populations. Through quantitative analysis of ligands on the surface of InAs CQDs, we find that (TMGe)₃As leads to In-rich characteristics, and we document the presence of an amorphous In-oleate shell on the surface. This we find causes surface defects, and thus, we develop materials processing strategies to remove the surface shell with a view to achieving efficient charge transfer in CQD solids. As a result, we develop resurfacing protocols, tailored to each dot synthesis, that produce balanced In-to-As stoichiometry regardless of synthetic input, enabling us to fabricate NIR photodetectors that achieve best-in-class EQEs at 940 nm excitons (25-28%, biased), independent of the synthetic pathway.

Two-dimensional (2D) hybrid perovskites harness the chemical and structural versatility of organic compounds. Here, we explore 2D perovskites that incorporate both a first organic component, a primary ammonium cation, and a second neutral organic module. Through the experimental examination of 42 organic pairs with a range of functional groups and organic backbones, we identify five crystallization scenarios that occur upon mixing. Only one leads to the cointercalation of the organic modules with distinct and extended interlayer spacing, which is observed with the aid of X-ray diffraction (XRD) pattern analysis combined with cross-sectional transmission electron microscopy (TEM) and elemental analysis. We present a picture in which complementary pairs, capable of forming intermolecular bonds, cocrystallize with multiple structural arrangements. These arrangements are a function of the ratio of organic content, annealing temperature, and substrate surface characteristics. We highlight how noncovalent bonds, particularly hydrogen and halogen bonding, enable the influence over the organic sublattice in hybrid halide perovskites.

Inverted perovskite solar cells (PSCs) promise enhanced operating stability compared to their normal-structure counterparts^1–3. To improve efficiency further, it is crucial to combine effective light management with low interfacial losses^4,5. Here we develop a conformal self-assembled monolayer (SAM) as the hole-selective contact on light-managing textured substrates. Molecular dynamics simulations indicate 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, thereby minimizing interfacial recombination and improving electronic structures. We report a lab-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 >1000 hours 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.

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 ).

Infrared photodetection enables depth imaging techniques such as structured light and time-of-flight. Traditional photodetectors rely on silicon (Si); however, the bandgap of Si limits photodetection to wavelengths shorter than 1100 nm. Photodetector operation centered at 1370 nm benefits from lower sunlight interference due to atmospheric absorption. Here, we report 1370 nm-operating colloidal quantum dot (CQD) photodetectors and evaluate their outdoor performance. We develop a surface-ligand engineering strategy to tune the electronic properties of each CQD layer and fabricate photodetectors in an inverted (PIN) architecture. The strategy enables photodetectors with an external quantum efficiency of 75% and a low dark current (1 μA/cm²). Outdoor testing demonstrates that CQD-based photodetectors combined with a 10 nm-line width bandpass filter centered at 1370 nm achieve over 2 orders of magnitude (140× at incident intensity 1 μW/cm²) higher signal-to-background ratio than do Si-based photodetectors that use an analogous bandpass filter centered at 905 nm.