Glycol bearing perylene monoimide based non-fullerene acceptors with increased dielectric permittivity.

Perylene monoimide based electron acceptors have great properties for use in organic solar cells, like thermal stability, strong absorption, and simple synthesis. However, they typically exhibit low values for the dielectric permittivity. This hinders efficient exciton dissociation, limiting the achievable power conversion efficiencies. In this work, we present the synthesis and utilization of two new acceptor-donor-acceptor (A-D-A) molecules, comprising perylene monoimide as electron withdrawing A unit. Oligo ethylene glycol side chain modified carbazole (PMI-[C-OEG]) and fluorene (PMI-[F-OEG]) linkers were used as electron rich D units, respectively. The polar side chains are expected to increase the polarizability of the molecules and, thus, their permittivity according to the Clausius-Mossotti relationship. We found that the incorporation of glycol chains improved the dielectric properties of both materials in comparison to the reference compounds with alkyl chains. The permittivity increased by 18% from 3.17 to 3.75 for the carbazole-based non-fullerene acceptor PMI-[C-OEG] and by 12% from 3.10 to 3.47 for the fluorene-based acceptor PMI-[F-OEG]. The fabricated solar cells revealed power conversion efficiencies of 3.71 ± 0.20% (record 3.92%) with PMI-[C-OEG], and 1.21 ± 0.06% (record 1.51%) with PMI-[F-OEG]. Supplementary Information: The online version contains supplementary material available at 10.1007/s00706-022-02956-2.

In Vitro Cytotoxicity of D18 and Y6 as Potential Organic Photovoltaic Materials for Retinal Prostheses.

Millions of people worldwide are diagnosed with retinal dystrophies such as retinitis pigmentosa and age-related macular degeneration. A retinal prosthesis using organic photovoltaic (OPV) semiconductors is a promising therapeutic device to restore vision to patients at the late onset of the disease. However, an appropriate cytotoxicity approach has to be employed on the OPV materials before using them as retinal implants. In this study, we followed ISO standards to assess the cytotoxicity of D18, Y6, PFN-Br and PDIN individually, and as mixtures of D18/Y6, D18/Y6/PFN-Br and D18/Y6/PDIN. These materials were proven for their high performance as organic solar cells. Human RPE cells were put in direct and indirect contact with these materials to analyze their cytotoxicity by the MTT assay, apoptosis by flow cytometry, and measurements of cell morphology and proliferation by immunofluorescence. We also assessed electrophysiological recordings on mouse retinal explants via microelectrode arrays (MEAs) coated with D18/Y6. In contrast to PFN-Br and PDIN, all in vitro experiments show no cytotoxicity of D18 and Y6 alone or as a D18/Y6 mixture. We conclude that D18/Y6 is safe to be subsequently investigated as a retinal prosthesis.

Wide-bandgap organic solar cells with a novel perylene-based non-fullerene acceptor enabling open-circuit voltages beyond 1.4 V.

A perylene-based acceptor (PMI-FF-PMI), consisting of two perylene monoimide (PMI) units bridged with a dihydroindeno[1,2-b]fluorene molecule was developed as a potential non-fullerene acceptor (NFA) for organic solar cells (OSCs). The synthesized NFA was combined with the high-performance donor polymer D18 to fabricate efficient OSCs. With an effective bandgap of 2.02 eV, the D18:PMI-FF-PMI blend can be categorized as a wide-bandgap OSC and is an attractive candidate for application as a wide-bandgap sub-cell in all-organic triple-junction solar cell devices. Owing to their large effective bandgap, D18:PMI-FF-PMI solar cells are characterized by an extremely high open-circuit voltage (V OC) of 1.41 V, which to the best of our knowledge is the highest reported value for solution-processed OSCs so far. Despite the exceptionally high V OC of this blend, a comparatively large non-radiative voltage loss (ΔV non-rad OC) of 0.25 V was derived from a detailed voltage loss analysis. Measurements of the electroluminescence quantum yield (ELQY) of the solar cell reveal high ELQY values of ∼0.1%, which contradicts the ELQY values derived from the non-radiative voltage loss (ΔV non-rad OC = 0.25 V, ELQY = 0.0063%). This work should help to raise awareness that (especially for BHJ blends with small ΔHOMO or ΔLUMO offsets) the measured ELQY cannot be straightforwardly used to calculate the ΔV non-rad OC. To avoid any misinterpretation of the non-radiative voltage losses, the presented ELQY discrepancies for the D18:PMI-FF-PMI system should encourage OPV researchers to primarily rely on the ΔV non-rad OC values derived from the presented voltage loss analysis based on EQEPV and J-V measurements.

Phenylene-Bridged Perylene Monoimides as Acceptors for Organic Solar Cells: A Study on the Structure-Property Relationship.

A series of non-fullerene acceptors based on perylene monoimides coupled in the peri position through phenylene linkers were synthesized via Suzuki-coupling reactions. Various substitution patterns were investigated using density functional theory (DFT) calculations in combination with experimental data to elucidate the geometry and their optical and electrochemical properties. Further investigations of the bulk properties with grazing incidence wide angle X-ray scattering (GIWAXS) gave insight into the stacking behavior of the acceptor thin films. Electrochemical and morphological properties correlate with the photovoltaic performance of devices with the polymeric donor PBDB-T and a maximum efficiency of 3.17 % was reached. The study gives detailed information about structure-property relationships of perylene-linker-perylene compounds.

Prototypical Organic-Oxide Interface: Intramolecular Resolution of Sexiphenyl on In2O3(111).

The performance of an organic semiconductor device is critically determined by the geometric alignment, orientation, and ordering of the organic molecules. Although an organic multilayer eventually adopts the crystal structure of the organic material, the alignment and configuration at the interface with the substrate/electrode material are essential for charge injection into the organic layer. This work focuses on the prototypical organic semiconductor para-sexiphenyl (6P) adsorbed on In2O3(111), the thermodynamically most stable surface of the material that the most common transparent conducting oxide, indium tin oxide, is based on. The onset of nucleation and formation of the first monolayer are followed with atomically resolved scanning tunneling microscopy and noncontact atomic force microscopy (nc-AFM). Annealing to 200 °C provides sufficient thermal energy for the molecules to orient themselves along the high-symmetry directions of the surface, leading to a single adsorption site. The AFM data suggests an essentially planar adsorption geometry. With increasing coverage, the 6P molecules first form a loose network with a poor long-range order. Eventually, the molecules reorient into an ordered monolayer. This first monolayer has a densely packed, well-ordered (2 × 1) structure with one 6P per In2O3(111) substrate unit cell, that is, a molecular density of 5.64 × 1013 cm-2.