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Modulated charge separation across (MO)/CH3NH3PbI3 and (MO)/PbI2/CH3NH3PbI3 (MO = TiO2, MoO3) interfaces was investigated by surface photovoltage (SPV) spectroscopy. Perovskite layers were deposited by solution‐based one‐step preparation and two‐step preparation methods. An unreacted PbI2 layer remained at the interface between the metal oxide and CH3NH3PbI3 for two‐step preparation. For the two‐step preparation on TiO2, the SPV signal related to absorption in CH3NH3PbI3 increased in comparison to the one‐step preparation due to electron transfer from CH3NH3PbI3 via PbI2 into TiO2 whereas the SPV signal related to defect transitions decreased. For the one‐step preparation on MoO3, holes photogenerated in CH3NH3PbI3 recombined with electrons in MoO3. In contrast, a hole transfer from CH3NH3PbI3 towards MoO3 was blocked by the PbI2 interlayer for the two‐step preparation on MoO3. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Local surface potential of Cu2ZnSnSe4 thin-films was investigated by Kelvin probe force microscopy. The surface potential profile across grain boundaries (GBs) shows a rise of 200–600 meV at GBs in a Cu-poor and Zn-poor film with 3.8% efficiency, which means positively charged GBs. In contrast, the GBs in a Cu-poor and Zn-rich film with 2% efficiency exhibit lowering of surface potential by 40 meV. The results indicate that GBs of Cu2ZnSnSe4 films play a role for exciton separation and governing defects for high efficiency could be not only CuZn but also VCu as explained theoretical predictions.

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Silver-based nanomaterials have been versatile building blocks of various photoassisted energy applications; however, they have demonstrated poor electrochemical catalytic performance and stability, in particular, in acidic environments. Here we report a stable and high-performance electrochemical catalyst of silver telluride (AgTe) for the hydrogen evolution reaction (HER), which was synthesized with a nanoporous structure by an electrochemical synthesis method. X-ray spectroscopy techniques on the nanometer scale and high-resolution transmission electron microscopy revealed an orthorhombic structure of nanoporous AgTe with precise lattice constants. First-principles calculations show that the AgTe surface possesses highly active catalytic sites for the HER with an optimized Gibbs free energy change of hydrogen adsorption (−0.005 eV). Our nanoporous AgTe demonstrates exceptional stability and performance for the HER, an overpotential of 27 mV, and a Tafel slope of 33 mV/dec. As a stable catalyst for hydrogen production, AgTe is comparable to platinum-based catalysts and provides a breakthrough for high-performance electrochemical catalysts.