Carrier control in Sn–Pb perovskites via 2D cation engineering for all-perovskite tandem solar cells with improved efficiency and stability

Nature Energy · 2022 · 273 citations

• Materials science
• Optoelectronics
• Nanotechnology

Metastable Dion-Jacobson 2D structure enables efficient and stable perovskite solar cells

Science · 2022 · 449 citations

• Materials science
• Crystallography
• Optoelectronics

The performance of three-dimensional (3D) organic-inorganic halide perovskite solar cells (PSCs) can be enhanced through surface treatment with 2D layered perovskites that have efficient charge transport. We maximized hole transport across the layers of a metastable Dion-Jacobson (DJ) 2D perovskite that tuned the orientational arrangements of asymmetric bulky organic molecules. The reduced energy barrier for hole transport increased out-of-plane transport rates by a factor of 4 to 5, and the power conversion efficiency (PCE) for the 2D PSC was 4.9%. With the metastable DJ 2D surface layer, the PCE of three common 3D PSCs was enhanced by approximately 12 to 16% and could reach approximately 24.7%. For a triple-cation–mixed-halide PSC, 90% of the initial PCE was retained after 1000 hours of 1-sun operation at ~40°C in nitrogen.

Surface reaction for efficient and stable inverted perovskite solar cells

Nature · 2022 · 1099 citations

• Materials science
• Nanotechnology
• Chemical engineering

Chiral-induced spin selectivity enables a room-temperature spin light-emitting diode

Science · 2021 · 724 citations

• Optoelectronics
• Materials science
• Condensed matter physics

In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.

Size-Dependent Janus-Ligand Shell Formation on PbS Quantum Dots

The Journal of Physical Chemistry C · 2021 · 4 citations

• Chemistry
• Crystallography
• Photochemistry

We studied the size-dependent Janus ligand shell formation on PbS QDs employing an X-type ligand exchange reaction between native oleate ligands and two substituted cinnamic acid ligands, trifluoromethyl- and dimethyl amino-cinnamic acid, representing electron donating and electron withdrawing ligands. The exchange reactions become significantly more favorable for both electron donating and withdrawing ligands (ΔG becomes more negative) in the smaller QDs compared to the larger QDs likely because the ligand density is smaller on the larger QDs reducing the strength of the ligand–ligand interactions. We found that Janus-ligand shells form more readily on smaller QDs than on bigger QDs with electron donating ligands. We also observed a dependence on the QD concentration that should be considered when forming Janus-ligand shells. Two-dimensional solution nuclear magnetic resonance spectroscopy (2D-NMR) shows evidence of pronounced phase segregation between oleate and electron donating ligands on the smaller QDs consistent with the enhanced ligand–ligand interactions. This study broadens our understanding of how to construct Janus and patchy ligand shell morphologies on small QDs.

Reconfiguring the band-edge states of photovoltaic perovskites by conjugated organic cations

Science · 2021 · 319 citations

• Chemistry
• Inorganic chemistry
• Materials science

(A, usually a monovalent organic cation; B, a divalent cation; and X, a halide anion) are constructed mainly of the orbitals from B and X sites. Hence, the structural and compositional varieties of the inorganic B-X framework are primarily responsible for regulating their electronic properties, whereas A-site cations are thought to only help stabilize the lattice and not to directly contribute to near-edge states. We report a π-conjugation-induced extension of electronic states of A-site cations that affects perovskite frontier orbitals. The π-conjugated pyrene-containing A-site cations electronically contribute to the surface band edges and influence the carrier dynamics, with a properly tailored intercalation distance between layers of the inorganic framework. The ethylammonium pyrene increased hole mobilities, improved power conversion efficiencies relative to that of a reference perovskite, and enhanced device stability.

Strategies to Achieve High Circularly Polarized Luminescence from Colloidal Organic–Inorganic Hybrid Perovskite Nanocrystals

ACS Nano · 2020 · 181 citations

• Materials science
• Nanotechnology
• Optoelectronics

from both as-synthesized and purified perovskite NCs at room temperature suggest a route to demonstrate colloidal NC-based spintronics.

Dynamic Ligand Surface Chemistry of Excited PbS Quantum Dots

The Journal of Physical Chemistry Letters · 2020 · 41 citations

• Chemistry
• Chemical physics
• Photochemistry

The ligand shell around colloidal quantum dots mediates the electron and energy transfer processes that underpin their use in optoelectronic and photocatalytic applications. Here, we show that the surface chemistry of carboxylate anchoring groups of oleate ligands passivating PbS quantum dots undergoes significant changes when the quantum dots are excited to their excitonic states. We directly probe the changes of surface chemistry using time-resolved mid-infrared spectroscopy that records the evolution of the vibrational frequencies of carboxylate groups following excitation of the electronic states. The data reveal a reduction of the Pb-O coordination of carboxylate anchoring groups to lead atoms at the quantum dot surfaces. The dynamic surface chemistry of the ligands may increase their surface mobility in the excited state and enhance the ability of molecular species to penetrate the ligand shell to undergo energy and charge transfer processes that depend sensitively on distance.

Transforming energy using quantum dots

Energy & Environmental Science · 2020 · 120 citations

• Optoelectronics
• Nanotechnology
• Physics

Optical energy can be transformed into electricity, photons, and chemical bonds using colloidal quantum dots as the scaffold.