Metrology plays a crucial role in semiconductor manufacturing by providing accurate and precise measurement and characterization of critical parameters. With the development of high-resolution extreme ultraviolet lithography (EUVL) processes, critical dimensions are shrinking to sub-10 nm. Resist materials encounter the challenge of providing heightened sensitivity and a handle on exacerbating stochastic variations. A comprehensive understanding of the chemical profile of the latent image is pivotal for mitigating stochastic effects and optimizing pattern quality. However, the subtle differences in chemistry between the exposed and unexposed regions of the resists make it extremely challenging to characterize the latent images with sub-nanometer precision. Here, we develop the metrology with critical-dimension resonant soft X-ray scattering (CD-RSoXS) to probe the chemical profiles of latent images stored in resist after exposure. The combination of absorption spectroscopy and enhanced scattering contrast makes it possible to characterize the subtle structural and chemical variations in the latent image. Moreover, the results of the measurements are compared with the simulations with a finite element method–based Maxwell solver to extract a detailed profile of the latent and developed images. We demonstrate that the CD-RSoXS technique can provide valuable insights into the high spatial resolution and local chemical sensitivity simultaneously, which is crucial to understanding the resolution limits and stochastic effects in EUVL processes.
Thermal transition of OSCs constituent materials are often insufficiently researched, resulting in trial-and-error rather than rational approaches to post-casting processing strategies to improve aggregation to enhance the power conversion efficiency. Despite the potential utility, little is known about the thermal transitions of the high-performance acceptors. Here, by using an optical method, we discover that the acceptor N3 has a clear solid-state aggregation transition at 82 °C. The transition informs and enables a double-annealing method that can fine‐tune aggregation and the device morphology. Compared with 16.6% efficiency for the control devices, higher efficiency of 17.6% is obtained through the improved protocol. Design of high-performance acceptors with yet lower aggregation transitions might be required to successfully transition to low thermal budget industrial processing methods where annealing temperatures on plastic substrates have to be kept low.
Organic solar cells based on D18:Y6 recently exhibited a record power conversion efficiency of over 18%. We have initially studied the molecular packing and thermodynamic properties of three D18:NFA blends by employing synchrotron X-ray techniques, secondary ion mass spectrometry and UV-vis miscibility measurements. The D18 polymer exhibits strong chain extension in films, which is beneficial to charge transport. Miscibility and other characterizations explain the disparate performance of three systems and the processing procedures. Our contribution reveals several unique property–performance relations of D18-based photovoltaic devices and help guide design or fabrication of yet higher efficiency organic solar cells.
Newly developed fused-ring electron acceptors (FREAs) have proven to be an effective class of materials for extending the absorption window and boosting the efficiency of organic photovoltaics (OPVs). While numerous FREA small molecules have been developed, there is surprisingly little structural diversity among high performance FREAs in literature. For example, of the high efficiency electron acceptors reported, the vast majority utilize derivatives of 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the acceptor moiety. It has been postulated that the high electron mobility exhibited by FREA molecules with INCN end groups is a result of close π-π stacking between the neighboring planar INCN groups, forming an effective charge transport pathway between molecules. To explore this as a design rationale for electron acceptors, we synthesized a new fused-ring electron acceptor, IDTCF, which has methyl substituents out of plane to the conjugated acceptor backbone. These methyl groups hinder packing and expand the π-π stacking distance by ~ 1 Å, but this change doesn’t affect the optical or electrochemical properties of the individual acceptor molecule. Overall, our results show that intermolecular interactions (especially π-π stacking between end groups) play a crucial role in performance of FREAs. We demonstrated that the planarity of the acceptor unit is of paramount importance as even minor deviations in end group distance are enough to disrupt crystallinity and cripple device performance.
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