Methylammonium lead iodide perovskite (CH3NH3PbI3) plays an important role in light absorption and carrier transport in efficient organic-inorganic perovskite solar cells. In this Letter, we report the first theoretical estimation of effective masses of photocarriers in CH3NH3PbI3. Effective masses of photogenerated electrons and holes were estimated to be me* = 0.23m0 and mh* = 0.29m0, respectively, including spin-orbit coupling effects. This result is consistent with the long-range ambipolar transport property and with the larger diffusion constant for electrons compared with that for holes in the perovskite, which enable efficient photovoltaic conversion.

The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current-voltage curves, which is considered to be a serious issue for PSCs' operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CHNHPbI (MAPbI). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects.

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For a nonaqueous sodium-ion battery (NIB), phosphorus materials have been studied as the highest-capacity negative electrodes. However, the large volume change of phosphorus upon cycling at low voltage causes the formation of new active surfaces and potentially results in electrolyte decomposition at the active surface, which remains one of the major limiting factors for the long cycling life of batteries. In this present study, powerful surface characterization techniques are combined for investigation on the electrode/electrolyte interface of the black phosphorus electrodes with polyacrylate binder to understand the formation of a solid electrolyte interphase (SEI) in alkyl carbonate ester and its evolution during cycling. The hard X-ray photoelectron spectroscopy (HAXPES) analysis suggests that SEI (passive film) consists of mainly inorganic species, which originate from decomposition of electrolyte solvents and additives. The thicker surface layer is formed during cycling in the additive-free electrolyte, compared to that in the electrolyte with fluoroethylene carbonate (FEC) or vinylene carbonate (VC) additive. The HAXPES and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) studies further reveal accumulation of organic carbonate species near the surface and inorganic salt decomposition species. These findings open paths for further improvement for the cyclability of phosphorus electrodes for high-energy NIBs.