All-solid lithium batteries are an attractive next-generation technology that use ion-conducting solids such as β-Li 3 PS 4 (LPS) to enable use of a lithium metal anode, which increases theoretical capacity and widens the stable voltage window over traditional lithium-ion systems. These ion-conductive solids also provide increased safety by replacing flammable liquid electrolytes. Although solid-state electrolytes are significantly more stable and dendrite-resistant than traditional liquid electrolytes, lithium anodes in all-solid systems may nevertheless grow dendrites under high stress or repeated cycling, leading to short circuits and premature battery breakdown. For this reason, we study the formation and propagation of Li metal features within solid electrolytes using synchrotron-based X-ray tomography with in-situ current-voltage cycling supported by our custom sample platform. Our results demonstrate the ability of this technique to delineate different layers of the Li/LPS/Li structure with spatial resolution approaching 1 μm. At this resolution, we are able to detect expansion of voids, especially in early stages of cycling. This expansion of voids is observed throughout the volume of the symmetric cells and visually resembles propagation of cracks resulting from interactions between the Li metal and pre-existing voids in the LPS electrolyte.
Using an analysis based on Marcus theory, we characterize losses in open-circuit voltage (V OC ) due to changes in charge-transfer state energy, electronic coupling, and spatial density of charge-transfer states in a series of polymer/fullerene solar cells. We use a series of indacenodithiophene polymers and their selenium-substituted analogs as electron donor materials and fullerenes as the acceptors. By combining device measurements and spectroscopic studies (including subgap photocurrent, electroluminescence, and, importantly, time-resolved photoluminescence of the chargetransfer state) we are able to isolate the values for electronic coupling and the density of charge-transfer states (N CT ), rather than the more commonly measured product of these values. We find values for N CT that are surprisingly large (∼4.5 × 10 21 −6.2 × 10 22 cm −3 ), and we find that a significant increase in N CT upon selenium substitution in donor polymers correlates with lower V OC for bulk heterojunction photovoltaic devices. The increase in N CT upon selenium substitution is also consistent with nanoscale morphological characterization. Using transmission electron microscopy, selected area electron diffraction, and grazing incidence wide-angle X-ray scattering, we find evidence of more intermixed polymer and fullerene domains in the selenophene blends, which have higher densities of polymer/fullerene interfacial charge-transfer states. Our results provide an important step toward understanding the spatial nature of charge-transfer states and their effect on the open-circuit voltage of polymer/fullerene solar cells.
optoelectronic devices in particular are an appealing alternative to current inorganic technologies, which suffer from limited modularity, intrinsic fragility, low speed, high power consumption, cryogenic cooling requirements, and epitaxial incompatibility with Si complementary metal-oxide-semiconductor (CMOS) processes. [12] The beneficial electronic properties of narrow gap OSCs, such as low exciton binding energies and facile charge extraction, stem from their strong intramolecular polarity and easily accessible carrier transport energy levels. [4,13,14] However, the strong intramolecular polarity also leads to dramatic and unexpected changes in photophysics, such as ultrafast exciton self-ionization, [13,14] emergence of low-energy dark states, [15] and singlet fission mediated by intramolecular charge-transfer character. [16,17] Rationally designing devices to employ these materials requires a deeper understanding of their unique photophysical properties.There is a nascent interest in polymeric materials with electronic absorption in the short-wave infrared (SWIR), where recent advances in synthetic techniques have pushed band gaps of solution-processable materials as low as ≈0.5 eV. [18][19][20][21][22] Although further development of structure-function relationships is required to reach even lower band gaps, thus far the successful engineering of narrow gap polymers has, in large part, followed a "push-pull" design strategy in which the energetic difference between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) is controlled by varying the electron Infrared organic photodetector materials are investigated using transient absorption spectroscopy, demonstrating that ultrafast charge generation assisted by polymer aggregation is essential to compensate for the energy gap law, which dictates that excited state lifetimes decrease as the band gap narrows. Short sub-picosecond singlet exciton lifetimes are measured in a structurally related series of infrared-absorbing copolymers that consist of alternating cyclopentadithiophene electron-rich "push" units and strong electron-deficient "pull" units, including benzothiadiazole, benzoselenadiazole, pyridalselenadiazole, or thiadiazoloquinoxaline. While the ultrafast lifetimes of excitons localized on individual polymer chains suggest that charge carrier generation will be inefficient, high detectivity for polymer:PC 71 BM infrared photodetectors is measured in the 0.6 < λ < 1.5 µm range. The photophysical processes leading to charge generation are investigated by performing a global analysis on transient absorption data of blended polymer:PC 71 BM films. In these blends, charge carriers form primarily at polymer aggregate sites on the ultrafast time scale (within our instrument response), leaving quickly decaying single-chain excitons unquenched. The results have important implications for the further development of organic infrared optoelectronic devices, where targeting processes such as excited state delocalization ov...
We use near edge X-ray absorption fine structure (NEXAFS) and resonant Auger spectroscopy combined with density functional theory (DFT) to investigate the electronic structure of the LUMO of two similar donor/acceptor-type polymers, PCPDTBT and PCDTBT, which are of interest for organic photovoltaic applications. We find the resonant Auger results to be independent of film morphology and likely dominated by localized structure rather than extended chain interactions. We show that the degree of excited state localization onto the benzothiadiazole acceptor group in each polymer is similar, suggesting that that the differences in IQE between these two polymers are not explained by the electronic structure of the LUMO.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.