In recent years, there have been significant efforts to understand the role of the electronic structure of redox active materials according to their performance and thermodynamic stability in electrochemical storage devices and to develop novel materials with higher energy density and higher power. It is generally recognized that transition metal compounds used as a positive electrode determine the specific capacity and the energy density of rechargeable batteries, while the charge transfer resistance at the electrolyte–electrode interface plays a key role in delivering the power of the electrochemical cell. In the present work, we study the stability of Li x Ni0.2Co0.7Mn0.1O2 thin films through the evolution of the occupied and unoccupied density of states as a function of the charging state of the electrode as well as the physicochemical conditions influencing the ionic transport across the electrode–electrolyte interface. A comprehensive experimental quasi in situ approach has been applied by using synchrotron X-ray photoelectron spectroscopy (SXPS) and O K-edge and Co, Ni, Mn L-edges XANES. Our experimental data demonstrate the change of the Fermi level position with Li+ removal and Ni2+ → Ni4+ and Co3+ → Co4+ changes of oxidation state for the charge compensation in the bulk of the material. As is evidenced by the experimentally determined energy band diagram of Li x≤1.0Ni0.2Co0.7Mn0.1O2 vs the evolution of the Fermi level, no hole transfer to the O2p bands is observed up to a charging state of 4.8 V, which evidences the thermodynamic stability of Li x≤1.0Ni0.2Co0.7Mn0.1O2 under high charging voltage in contrast to LiCoO2. A very thin solid electrolyte interface layer (less than 30 Å thickness) on the Li x≤1.0Ni0.2Co0.7Mn0.1O2 film is formed in a decomposition reaction of the electrolyte also involving the transition metal oxide. The enhanced concentration of lithium in the interface layer correlates evidently with the electron transfer to the transition metal sites changing their electronic configuration. It is concluded that Li x≤1.0Ni0.2Co0.7Mn0.1O2 can serve as a high energy density cathode material, but the delivery of high power, which is a critical parameter for an electric vehicle, is strongly influenced by the physicochemical conditions at the solid electrolyte interface, which can suppress Li+ diffusion or even block the Li+ paths across the interface.

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Surface layers at the cathode-electrolyte interface strongly affect the performance of the Li-ion cell. Such surface layers are found during manufacturing and operation of the battery. As water can never be fully excluded from the manufacturing chain, it will form an additional surface layer situated between cathode and electrolyte. In this contribution, we investigate the interaction between the LiCoO 2 electrode and H 2 O by a surface science approach. H 2 O was adsorbed stepwise onto a LiCoO 2 thin film, and intermediate X-ray photoelectron spectroscopy analysis was performed after every step. Adsorption results in the formation of a Li 2 O/LiOH-type reaction layer on top of the electrode and downward band bending attributed to a Li + -ion transfer out of the electrode.

We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of 340° C, which is much lower than that used in conventional processes (>500 ° C). The CdTe films were treated with the usual CdCl 2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub 340°C) compared to high-temperature cells (Tsub = 520°C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposition parameters on the solar cell performance is investigated by using three different sets of parameters with different deposition rates and substrate temperatures for the CdS preparation. Efficiencies about 10.9% with a copper-free back contact and 12.0% with a copper-containing back contact were achieved using the low temperature CdTe process

The electrical properties of (Ba, Sr)TiO(3) (BST) thin films are studied using different combinations of Pt and tin-doped indium oxide (In(2)O(3):Sn, ITO) as electrode material. With Pt as bottom and top electrode the films show insulating behaviour with a low leakage current. A rectifying current-voltage characteristic is obtained by replacing the top electrode with ITO. As shown by photoemission as well as by electrical measurements, the property of the BST/ITO interface depends strongly on the deposition sequence, and can be related to the level of oxidation of the ITO film. Highly doped ITO as top electrode forms an Ohmic contact with BST. This enables the preparation of highly rectifying diodes that exhibit a space-charge-limited current behaviour. Larger barriers are obtained when ITO is used as bottom electrode. This is related to the oxidation of the ITO layer during BST deposition and results in a low interface-limited current. Due to the large energy gaps of both BST and ITO, the combination of these materials provides an additional route to transparent electronics.