Positive Feedback Mechanism of Probe Sonication for the Perovskite Films in Solar Cells

The performance of perovskite solar cells (PSCs) is governed by the quality of perovskite films, whereby compact, pinhole-free perovskite films are desired, in addition to its composition. We have demonstrated probe sonication as a processing technique to provide positive feedback for enhancing the perovskite film quality and photovoltaic parameters, with two systems, CH3NH3PbI3 (MAPbI3) and Cs0.17FA0.83Pb(I0.83Br0.17)3. In probe sonication, the ultrasound results in the formation, growth, and collapse of the bubbles through shock wave inside the gas phase of the collapsing bubble. This phenomenon has a chemical impact on the nucleation of the perovskite phases and interconnectivity of the grains. The 60 min sonicated films with stronger hydrogen bonding network are devoid of unwanted Pb0, δ-FAPbI3, and PbI2 phases, having tightly packed homogeneous grains, minimum electron-hole recombination pathways, and improved light absorption. The surface potential remains mostly unaltered across the grains and grain boundaries, and the realignment of the Fermi energy (EF) favors facile carrier transport. The photoconversion efficiency (PCE) of the MAPbI3 and Cs0.17FA0.83Pb(I0.83Br0.17)3 devices is improved by 28.1 and 17.2% in comparison to the pristine perovskites, respectively. The 60 min sonicated Cs0.17FA0.83Pb(I0.83Br0.17)3 PSC has 20.20 ± 0.40% PCE with 1000 h ambient stability having >60% retention of the original PCE.

Synthesis of neutral Li-endohedral PCBM: an n-dopant for fullerene derivatives

Li@PCBM, the first neutral Li@C₆₀ derivative, was synthesized. The Li@PCBM exists in a monomer-dimer equilibrium in solution but as a monomer in the PCBM matrix. The fully dispersed Li@PCBM n-doped the surrounding empty PCBM, raising the Fermi level by 0.13 eV compared with the undoped PCBM film. The hybrid films were utilized as an ETL for PSCs, promoting the efficiency of the device.

Direct Visualization of Nearly Free Electron States Formed by Superatom Molecular Orbitals in a Li@C60 Monolayer

Using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we directly determine the spatial and energetic distributions of superatom molecular orbitals (SAMOs) of an Li@C₆₀ monolayer adsorbed on a Cu(111) surface. Utilizing a weakly bonded [Li⁺@C₆₀] NTf₂^- (NTf₂^-: bis(trifluoromethanesulfonyl)imide) salt makes it possible to produce a Li@C₆₀ monolayer with high concentration of Li@C₆₀ molecules. Because of the very uniform adsorption geometry of Li@C₆₀ on Cu(111), the p_z-SAMO, populated above the upper hemisphere of the molecule, exhibits an isotropic and delocalized nature, with an energy that is significantly lower compared to that of C₆₀. The isotropic overlapping of p_z-SAMOs in the condensed monolayer of Li@C₆₀ results in a laterally homogeneous STM image contributing to the formation of a free-electron-like states. These findings make an important step toward further basic research and applicative utilization of Li@C₆₀ SAMOs.

Environmentally Compatible Lead-Free Perovskite Solar Cells and Their Potential as Light Harvesters in Energy Storage Systems

Next-generation renewable energy sources and perovskite solar cells have revolutionised photovoltaics research and the photovoltaic industry. However, the presence of toxic lead in perovskite solar cells hampers their commercialisation. Lead-free tin-based perovskite solar cells are a potential alternative solution to this problem; however, numerous technological issues must be addressed before the efficiency and stability of tin-based perovskite solar cells can match those of lead-based perovskite solar cells. This report summarizes the development of lead-free tin-based perovskite solar cells from their conception to the most recent improvements. Further, the methods by which the issue of the oxidation of tin perovskites has been resolved, thereby enhancing the device performance and stability, are discussed in chronological order. In addition, the potential of lead-free tin-based perovskite solar cells in energy storage systems, that is, when they are integrated with batteries, is examined. Finally, we propose a research direction for tin-based perovskite solar cells in the context of battery applications.

Endocircular Li Carbon Rings

By employing accurate state-of-the-art many-electron quantum-chemistry methods, we establish that monocyclic carbon rings can accommodate Li guest atoms. The low-lying electronic states of these endocircular systems are analyzed and found to include both charge-separated states where the guest Li atom appears as a cation and the ring as an anion and encircled-electron states where Li and the ring are neutral. The electron binding energies of the encircled-electron states increase drastically at their highly symmetric equilibrium geometries with increasing size of the ring, and in Li@C24 , this state becomes the ground state. Li is very weakly bound vertical to the rings in the low-lying encircled-electron states, hinting to van-der-Waals binding. Applcations are mentioned.

Caged-electron states and split-electron states in the endohedral alkali C60

The low-lying electronic states of neutral X@C60 (X = Li, Na, K, Rb) have been computed and analyzed by employing state-of-the-art high level many-electron methods. Apart from the common charge-separated states, well known to be present in endohedral fullerenes, one non-charge-separated state has been found in each of the investigated systems. In Li@C60 and Na@C60, the non-charge-separated state is a caged-electron state already discussed before for Li@C60. This indicates that the application of this low-lying state of Li@C60 discussed before is also applicable for Na@C60. In K@C60 and Rb@C60, the electronic radial distribution analysis shows that this hitherto unknown non-charge-separated state possesses a different nature from that of a caged-electron state.

Antigen down format photoelectrochemical analysis supported by fullerene functionalized Sn3O4

Herein, a smart competitive-type photoelectrochemical (PEC) sensor based on an antigen-down (Ag-down) format for procalcitonin (PCT) detection is proposed. A fullerene sensitized flower-like Sn₃O₄ nano-structure is used as the photoactive platform, and FeS₂ is labeled on the secondary antibody as a signal adjusting element. The sensor exhibits excellent sensitivity and great stability.

Oxidation states of gallium (infrequent i and common iii) tunable via medium-sized C60 and small-sized C28 fullerenes

Differently sized fullerenes are shown to be flexible tools for tuning the oxidation states of gallium, and a fluoridation strategy facilitates the further stabilization of Ga@I_h(1812)-C₆₀.

Caged-Electron States in Endohedral Li Fullerenes

By employing large-scale high-level EA-EOM-CCSD calculations, we have computed and analyzed the low-lying states of neutral Li@C₆₀. Apart from one state, all states are found to be charge-separated states of the type Li⁺@C₆₀^-. The new state is the first reported non-charge-separated state in endohedral alkali fullerenes. This caged-electron state is analyzed in detail. Arguments are given that in larger highly symmetric endohedral fullerenes the caged-electron state can be the electronic ground state of the system. HF and DFT calculations on Li@C₁₈₀ indeed find that the caged-electron state is the ground state and that in its equilibrium geometry Li sits at the center of the cage. Applications are mentioned.