Charge-transfer biexciton annihilation in a donor-acceptor co-crystal yields high-energy long-lived charge carriers.

Organic donor-acceptor (D-A) co-crystals have attracted much interest due to their important optical and electronic properties. Co-crystals having ⋯DADA⋯ π-stacked morphologies are especially interesting because photoexcitation produces a charge-transfer (CT) exciton, D˙-A˙, between adjacent D-A molecules. Although several studies have reported on the steady-state optical properties of this type of CT exciton, very few have measured the dynamics of its formation and decay in a single D-A co-crystal.

Simultaneous Bottom-Up Interfacial and Bulk Defect Passivation in Highly Efficient Planar Perovskite Solar Cells using Nonconjugated Small-Molecule Electrolytes.

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. Here nonconjugated multi-zwitterionic small-molecule electrolytes (NSEs) are introduced, which act not only as charge-extracting layers for barrier-free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom-up passivation effect. Implementing these synergistic properties affords NSE-based planar PSCs that deliver a remarkable power conversion efficiency of 21.

Photovoltaic Blend Microstructure for High Efficiency Post-Fullerene Solar Cells. To Tilt or Not To Tilt?

Achieving efficient polymer solar cells (PSCs) requires a structurally optimal donor-acceptor heterojunction morphology. Here we report the combined experimental and theoretical characterization of a benzodithiophene-benzothiadiazole donor polymer series (PBTZF4-R; R = alkyl substituent) blended with the non-fullerene acceptor ITIC-Th and analyze the effects of substituent dimensions on blend morphology, charge transport, carrier dynamics, and PSC metrics. Varying substituent dimensions has a pronounced effect on the blend morphology with a direct link between domain purity, to some extent domain dimensions, and charge generation and collection.

Tunable Crystallinity and Charge Transfer in Two-Dimensional G-Quadruplex Organic Frameworks.

DNA G-quadruplex structures were recently discovered to provide reliable scaffolding for two-dimensional organic frameworks due to the strong hydrogen-bonding ability of guanine. Herein, 2,7-diaryl pyrene building blocks with high HOMO energies and large optical gaps are incorporated into G-quadruplex organic frameworks. The adjustable substitution on the aryl groups provides an opportunity to elucidate the framework formation mechanism; molecular non-planarity is found to be beneficial for restricting interlayer slippage, and the framework crystallinity is highest when intermolecular interaction and non-planarity strike a fine balance.

Hole-Transfer Dependence on Blend Morphology and Energy Level Alignment in Polymer: ITIC Photovoltaic Materials.

Bulk-heterojunction organic photovoltaic materials containing nonfullerene acceptors (NFAs) have seen remarkable advances in the past year, finally surpassing fullerenes in performance. Indeed, acceptors based on indacenodithiophene (IDT) have become synonymous with high power conversion efficiencies (PCEs). Nevertheless, NFAs have yet to achieve fill factors (FFs) comparable to those of the highest-performing fullerene-based materials.

Atomistic Approach toward Selective Photocatalytic Oxidation of a Mustard-Gas Simulant: A Case Study with Heavy-Chalcogen-Containing PCN-57 Analogues.

Here we describe the synthesis of two Zr-based benzothiadiazole- and benzoselenadiazole-containing metal-organic frameworks (MOFs) for the selective photocatalytic oxidation of the mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). The photophysical properties of the linkers and MOFs are characterized by steady-state absorption and emission, time-resolved emission, and ultrafast transient absorption spectroscopy. The benzoselenadiazole-containing MOF shows superior catalytic activity compared to that containing benzothiadiazole with a half-life of 3.

Charge Separation Mechanisms in Ordered Films of Self-Assembled Donor-Acceptor Dyad Ribbons.

Orthogonal attachment of polar and nonpolar side-chains to a zinc porphyrin-perylenediimide dyad (ZnP-PDI, 1a) is shown to result in self-assembly of ordered supramolecular ribbons in which the ZnP and PDI molecules form segregated π-stacked columns. Following photoexcitation of the ordered ribbons, ZnP-PDI radical ion pairs form in <200 fs and subsequently produce a 30 ± 3% yield of free charge carriers that live for about 100 μs. Elongating the side chains on ZnP and PDI in 1b enhances the order of the films, but does not result in an increase in free charge carrier yield.

Direct Observation of a Charge-Transfer State Preceding High-Yield Singlet Fission in Terrylenediimide Thin Films.

Singlet exciton fission (SF) in organic chromophore assemblies results in the conversion of one singlet exciton (S) into two triplet excitons (T), provided that the overall process is exoergic, i.e., E(S) > 2E(T).

TiO-ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells.

Achieving high open-circuit voltage (V) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the V and photovoltaic performance of formamidinium tin iodide (FASnI) perovskite solar cells. The TiO-ZnS electron transporting layer (ETL) with cascade conduction band structure can effectively reduce the interfacial charge recombination and facilitate electron transfer.