Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells. Nature Materials.

The frontier molecular energy levels of organic semiconductors are decisive for their fundamental function and efficiency in optoelectronics. However, the precise determination of these energy levels and their variation when using different techniques makes it hard to compare and establish design rules. In this work, the energy levels of 33 organic semiconductors via cyclic voltammetry (CV), density functional theory, ultraviolet photoelectron spectroscopy, and low‐energy inverse photoelectron spectroscopy are determined. Solar cells are fabricated to obtain key device parameters and relate them to the significant differences in the energy levels and offsets obtained from different methods. In contrast to CV, the photovoltaic gap measured using photoelectron spectroscopy (PES) correlates well with the experimental device VOC. It is demonstrated that high‐performing systems such as PM6:Y6 and WF3F:Y6, which are previously reported to have negligible ionization energy (IE) offsets (ΔIE), possess sizable ΔIE of ≈0.5 eV, determined by PES. Using various D–A blends, it is demonstrated that ΔIE plays a key role in charge generation. In contrast to earlier reports, it is shown that a vanishing ΔIE is detrimental to device performance. Overall, these findings establish a solid base for reliably evaluating material energetics and interpreting property–performance relationships in organic solar cells.

Time-resolved photoluminescence (TRPL) spectroscopy is a powerful technique to investigate excited charge carrier recombinations in semiconductors and molecular systems. The analysis of the TRPL decays of many molecular systems (e.g....

Low dimensional semiconductor quantum dots (<10 nm) have received great attention for potential use in biomedical applications (diagnosis and therapy) for which larger nanoparticles (>10 nm) are not suitable. Here, we demonstrate a green, biogenic synthesis route for making CdS quantum dots (QDs) with 2-5 nm particle size using tea leaf extract (Camellia sinensis) as a toxic-free particle stabilizing agent. We have explored the biological activity of these CdS QDs in different applications, namely; a) antibacterial activity b) bioimaging and c) apoptosis of lung cancer cells. The antibacterial activity of the CdS QDs has been studied against different types of bacteria growth, showing that CdS QDs effectively inhibit the bacterial growth and exhibit cytotoxicity towards A549 cancer cells when compared to a control (no QD treatment). We have compared this cytotoxicity effect on A549 cancer cells with a standard drug, cisplatin, showing comparable results. Additionally, these CdS QDs produce high contrast fluorescence images of A549 cancer cells indicating a strong interaction with the cancer cell. To further understand the role of CdS QDs in bioimaging and cytotoxicity effect in A549 cells, fluorescence emission and flow cytometry analysis were carried out. The fluorescence emission of CdS QDs were recorded with λexc= 410 nm, showing concentration dependence fluorescence emission centered at 670 nm. From the flow cytometry analysis, it is confirmed that the CdS QDs are arresting the A549 cell growth at the S phase of cell cycle, inhibiting further growth of lung cancer cell. The multifunctional advantages of Camellia sinensis extract mediated green CdS QDs will be of widespread interest in implementing in-vivo based bioimaging and therapeutic cancer treatment applications.

The photochemistry and stability of fullerene films is found to be strongly dependent upon film nanomorphology. In particular, PCBM blend films, dispersed with polystyrene, are found to be more susceptible to photobleaching in air than the more aggregated neat films. This enhanced photobleaching correlated with increased oxygen quenching of PCBM triplet states and the appearance of a carbonyl FTIR absorption band indicative of fullerene oxidation, suggesting PCBM photo-oxidation is primarily due to triplet-mediated singlet oxygen generation. PCBM films were observed to undergo photo-oxidation in air for even modest (≤40 min) irradiation times, degrading electron mobility substantially, indicative of electron trap formation. This conclusion is supported by observation of red shifts in photo- and electro-luminescence with photo-oxidation, shown to be in agreement with time-dependent density functional theory calculations of defect generation. These results provide important implications on the environmental stability of PCBM-based films and devices.