The deployment of Li‐garnet Li₇La₃Zr₂O₁₂ (LLZO) solid‐state electrolytes in solid‐state batteries is severely hampered by their poor wettability with metallic Li. In this work, Sb is presented as a compelling interfacial layer allowing superior wetting of Li onto a LLZO surface, resulting in a remarkably low Li/LLZO interfacial resistance of 4.1(1) Ω cm². An atomistic insight into Sb‐coated LLZO interface using soft and hard X‐ray photoelectron spectroscopy and focused ion beam time‐of‐flight secondary ion mass spectrometry shows the formation of a Li‐Sb alloy as an interlayer. It is determined that the Li/Sb‐coated LLZO/Li symmetrical cells exhibit a high critical current density of up to 0.64 mA cm⁻² and low overpotentials of 40–50 mV at a current density of 0.2 mA cm⁻² without applying external pressure. The electrochemical performance of Sb coated‐LLZO pellets is also assessed with an intercalation‐type V₂O₅ cathode. Li/Sb‐coated‐LLZO/V₂O₅ full cells deliver stable capacities of around 0.45 mAh cm⁻², with a peak current density of 0.3 mA cm⁻².

Attempts to improve the efficiency of kesterite solar cells by changing the intrinsic stoichiometry have not helped to boost the device efficiency beyond the current record of 12.6%. In this light, the addition of extrinsic elements to the Cu₂ZnSn(S,Se)₄ matrix in various quantities has emerged as a popular topic aiming to ameliorate electronic properties of the solar cell absorbers. This article reviews extrinsic doping and alloying concepts for kesterite absorbers with the focus on those that do not alter the parent zinc-blende derived kesterite structure. The latest state-of-the-art of possible extrinsic elements is presented in the order of groups of the periodic table. The highest reported solar cell efficiencies for each extrinsic dopant are tabulated at the end. Several dopants like alkali elements and substitutional alloying with Ag, Cd or Ge have been shown to improve the device performance of kesterite solar cells as compared to the nominally undoped references, although it is often difficult to differentiate between pure electronic effects and other possible influences such as changes in the crystallization path, deviations in matrix composition and presence of alkali dopants coming from the substrates. The review is concluded with a suggestion to intensify efforts for identifying intrinsic defects that negatively affect electronic properties of the kesterite absorbers, and, if identified, to test extrinsic strategies that may compensate these defects. Characterization techniques must be developed and widely used to reliably access semiconductor absorber metrics such as the quasi-Fermi level splitting, defect concentration and their energetic position, and carrier lifetime in order to assist in search for effective doping/alloying strategies.

The high ionic conductivity and wide electrochemical stability of the lithium garnet Li₇La₃Zr₂O₁₂ (LLZO) make it a viable solid electrolyte for all‐solid‐state lithium batteries with superior capacity and power densities. Contrary to common ceramic processing routes of bulk pellets, thin film solid electrolytes could enable large‐area fabrication, and increase energy and power densities by reducing the bulkiness, weight and critically, the area‐specific resistance of the electrolyte. Fabrication of LLZO films has nonetheless been challenging because of lithium losses and formation of impurity phases that result in low densities and poor ionic conductivities as compared to bulk pellets. Here, a scalable method for fabricating submicron films of LLZO employing co‐sputtering from doped LLZO and Li₂O targets is presented. A record ionic conductivity of 1.9 × 10⁻⁴ S cm^–1 is measured for dense and uniform cubic‐phase Ga‐substituted LLZO films annealed at 700 °C in oxygen, which is comparable to the values in high‐temperature sintered pellets and outperforms by one order of magnitude the latest record for LLZO thin films as well as the typical conductivities in the well‐established LiPON electrolyte. This result is an important milestone to realize all‐vacuum deposited solid‐state batteries with higher power density.

Lithium dendrites have become a roadblock in the realization of solid-state batteries with lithium metal as high-capacity anode. The presence of surface and bulk defects in crystalline electrolytes such as the garnet Li₇La₃Zr₂O₁₂ (LLZO) facilitates the growth of these hazardous lithium filaments. Here we explore the amorphous phase of LLZO as a lithium dendrite shield owing to its grain-boundary-free microstructure, stability against lithium metal, and high electronic insulation. By tuning the lithium stoichiometry, the ionic conductivity can be increased by 4 orders of magnitude while retaining a negligible electronic conductivity. In symmetric cells, plating-stripping shows no signs of lithium penetration up to 3.2 mA cm⁻². The dense conformal nature of the films enables microbatteries with an electrolyte thickness of only 70 nm, which can be cycled at 10C for over 500 cycles. The application of this material as a coating on crystalline LLZO lowers the interface resistance and increases the critical current density. The effectiveness of the amorphous Li-La-Zr-O as dendrite blocking layer can accelerate the development of better solid-state batteries.