Zhen‐Kun Tang

Methylammonium lead iodide perovskite, CH3NH3PbI3 (MAPbI3), has made great progress in its efficiency as used in solid-state solar cells during recent years. Meanwhile, the degradation of its performance in moisture has attracted great attention, but the specific mechanism is not yet fully established. The water effects on the detailed structure and properties of the perovskite CH3NH3PbI3 have been carefully explored based on first-principles calculations. The results reveal that the water adsorption energy on the CH3NH3PbI3 (001) surface is ∼0.30 eV, while the water can easily penetrate into the surface in the form of molecular state owing to the huge interspace of CH3NH3PbI3, which can further corrode down the whole structure gradually. More importantly, the deformation of the structure greatly affects the electronic structure, which decreases the optical absorption. Such work paves an important way to understand the initial degradation progress of the perovskite structure under the humidity condition, which should help to optimize the structure to prevent the penetration of water in the system.

The substantial capacity gap between available anode and cathode materials for commercial Li-ion batteries (LiBs) remains, as of today, an unsolved problem. Oxygen vacancies (OVs) can promote Li-ion diffusion, reduce the charge transfer resistance, and improve the capacity and rate performance of LiBs. However, OVs can also lead to accelerated degradation of the cathode material structure, and from there, of the battery performance. Understanding the role of OVs for the performance of layered lithium transition metal oxides holds great promise and potential for the development of next generation cathode materials. This review summarises some of the most recent and exciting progress made on the understanding and control of OVs in cathode materials for Li-ion battery, focusing primarily on Li-rich layered oxides. Recent successes and residual unsolved challenges are presented and discussed to stimulate further interest and research in harnessing OVs towards next generation oxide-based cathode materials.

Abstract The suitable band structure is vital for perovskite solar cells, which greatly affect the high photoelectric conversion efficiency. Cation substitution is an effective approach to tune the electric structure, carrier concentration, and optical absorption of hybrid lead iodine perovskites. In this work, the electronic structures and optical properties of cation (Bi, Sn, and TI) doped tetragonal formamidinium lead iodine CH(NH 2 ) 2 PbI 3 (FAPbI 3 ) are studied by first-principles calculations. For comparison, the cation-doped tetragonal methylammonium lead iodine CH 3 NH 3 PbI 3 (MAPbI 3 ) are also considered. The calculated formation energies reveal that the Sn atom is easier to dope in the tetragonal MAPbI 3 /FAPbI 3 structure due to the small formation energy of about 0.3 eV. Besides, the band gap of Sn-doped MAPbI 3 /FAPbI 3 is 1.30/1.40 eV, which is considerably smaller than the un-doped tetragonal MAPbI 3 /FAPbI 3 . More importantly, compare with the un-doped tetragonal MAPbI 3 /FAPbI 3 , the Sn-doped MAPbI 3 and FAPbI 3 have the larger optical absorption coefficient and theoretical maximum efficiency, especially for Sn-doped FAPbI 3 . The lower formation energy, suitable band gap and outstanding optical absorption of the Sn-doped FAPbI 3 make it promising candidates for high-efficient perovskite cells.