Fused‐ring core nonfullerene acceptors (NFAs), designated “Y‐series,” have enabled high‐performance organic solar cells (OSCs) achieving over 18% power conversion efficiency (PCE). Since the introduction of these NFAs, much effort has been expended to understand the reasons for their exceptional performance. While several studies have identified key optoelectronic properties that govern high PCEs, little is known about the molecular level origins of large variations in performance, spanning from 5% to 18% PCE, for example, in the case of PM6:Y6 OSCs. Here, a combined solid‐state NMR, crystallography, and molecular modeling approach to elucidate the atomic‐scale interactions in Y6 crystals, thin films, and PM6:Y6 bulk heterojunction (BHJ) blends is introduced. It is shown that the Y6 morphologies in BHJ blends are not governed by the morphology in neat films or single crystals. Notably, PM6:Y6 blends processed from different solvents self‐assemble into different structures and morphologies, whereby the relative orientations of the sidechains and end groups of the Y6 molecules to their fused‐ring cores play a crucial role in determining the resulting morphology and overall performance of the solar cells. The molecular‐level understanding of BHJs enabled by this approach will guide the engineering of next‐generation NFAs for stable and efficient OSCs.
The charge generation–recombination dynamics in three narrow‐bandgap near‐IR absorbing nonfullerene (NFA) based organic photovoltaic (OPV) systems with varied donor concentrations of 40%, 30%, and 20% are investigated. The dilution of the polymer donor with visible‐range absorption leads to highly transparent active layers with blend average visible transmittance (AVT) values of 64%, 70%, and 77%, respectively. Opaque devices in the optimized highly reproducible device configuration comprising these transparent active layers lead to photoconversion efficiencies (PCEs) of 7.0%, 6.5%, and 4.1%. The investigation of these structures yields quantitative insights into changes in the charge generation, non‐geminate charge recombination, and extraction dynamics upon dilution of the donor. Lastly, this study gives an outlook for employing the highly transparent active layers in semitransparent organic photovoltaics (ST‐OPVs).
We propose co-solvent vapor annealing (SVA) as an effective post-treatment process to improve the quality of crystals and grains for high-efficiency perovskite solar cells.
Photoactive Materials
Next‐generation photovoltaics will be lightweight, flexible, and (semi)transparent. Highly transparent organic photoactive materials are reported by Thuc‐Quyen Nguyen, Viktor Brus, and co‐workers in article number 2203796. The changes in the fundamental processes in solar cells comprising a near‐IR‐absorbing acceptor and a visible‐light‐absorbing donor are revealed upon dilution of the donor material, paving the way for integrated energy‐harvesting solutions based on semitransparent organic photovoltaics.
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