We present a study of the energy levels present in a perovskite solar cell using Kelvin probe and UV air photoemission measurements. By constructing a detailed map of the energy levels in the system we are able to predict the maximum open circuit voltage of the solar cell.

A metal-organic hybrid perovskite (CH3NH3PbI3) with three-dimensional framework of metal-halide octahedra has been reported as a low-cost, solution-processable absorber for a thin-film solar cell with a power-conversion efficiency over 20%. Low-dimensional layered perovskites with metal halide slabs separated by the insulating organic layers are reported to show higher stability, but the efficiencies of the solar cells are limited by the confinement of excitons. In order to explore the confinement and transport of excitons in zero-dimensional metal–organic hybrid materials, a highly orientated film of (CH3NH3)3Bi2I9 with nanometre-sized core clusters of Bi2I9 3− surrounded by insulating CH3NH3 + was prepared via solution processing. The (CH3NH3)3Bi2I9 film shows highly anisotropic photoluminescence emission and excitation due to the large proportion of localised excitons coupled with delocalised excitons from intercluster energy transfer. The abrupt increase in photoluminescence quantum yield at excitation energy above twice band gap could indicate a quantum cutting due to the low dimensionality.

Photocatalytic conversion of cellulose to sugars and carbon dioxide with simultaneous production of hydrogen assisted by cellulose decomposition under UV or solar light irradiation was achieved upon immobilization of cellulose onto a TiO2 photocatalyst. This approach enables production of hydrogen from water without using valuable sacrificial agents, and provides the possibility for recovering sugars as liquid fuels.

Compared to traditional deposition techniques, in situ growth of nanoparticles on material surfaces is one of the more time- and cost-effective ways to design new catalysts. The B-site transition-metal cations in perovskite lattice could be partially exsolved as nanoparticles under reducing conditions, greatly enhancing catalytic activity. Here, we demonstrate that growing nanoparticles on the surface of a layered perovskite La0.8Sr1.2Fe0.9Co0.1O4±δ (LSFC), which could be applied as a redox stable and active electrode for intermediate-temperature symmetrical solid oxide fuel cells (IT-SSOFCs). Substitution of a proper amount of Co into the layered perovskite can thus optimize cathode and anode performance simultaneously. For example, the polarization resistances (R p) of LSFC electrode at 800 °C are 0.29 and 1.14 Ω cm2 in air and in 5% H2/N2 respectively, which are much smaller compared with the R p of Co-free La0.8Sr1.2FeO4±δ. The lower polarization resistance for LSFC in air can be mainly attributed to the enhanced electrical conductivity through the partial substitution of iron by cobalt in La0.8Sr1.2FeO4±δ. Meanwhile, the electrocatalytic activity of H2 greatly improved, because of the formation of exsolved homogeneous Co0 nanoparticles on the surface of LSFC, which appears to promote hydrogen oxidation reaction. Lower polarization resistance of 0.21 Ω cm2 in air and 0.93 Ω cm2 in 5% H2/N2 at 800 °C could be obtained further by examining an LSFC–Gd0.1Ce0.9O2−δ (CGO) composite as an electrode for IT-SSOFCs.

Perovskite electrodes have been considered as an alternative to Ni-YSZ cermet-based anodes as they afford better tolerance towards coking and impurities and due to redox stability can allow very high levels of fuel utilisation. Unfortunately performance levels have rarely been sufficient, especially for a second generation anode supported concept. A-site deficient lanthanum and calcium co-doped SrTiO3, La0.2Sr0.25Ca0.45TiO3 (LSCTA-) shows promising thermal, mechanical and electrical properties and has been investigated in this study as a potential anode support material for SOFCs. Flat multilayer ceramics cells were fabricated by aqueous tape casting and co-sintering, comprising a 450-µm thick porous LSCTA-scaffold support, a dense YSZ electrolyte and a thin layer of La0.8Sr0.2CoO3-δ (LSC)-La0.8Sr0.2FeO3-δ ( LSF)-YSZ cathode. Impregnation of a small content of Ni significantly enhanced fuel cell performance over naked LSCTA-. Use of ceria as a co-catalyst was found to improve the microstructure and stability of impregnated Ni and this in combination with the catalytic enhancement from ceria significantly improved performance over Ni impregnation alone. With addition of CeO2 and Ni to a titanate scaffold anode that had been pre-reduced at 1000 o C, a maximum powder density of 0.96Wcm -2 can be achieved at 800 o C using humidified hydrogen as fuel. The encouraging results show that an oxide anode material, LSCTA-can be used as anode support with YSZ electrolyte heralding a new option for SOFC development.

No abstract

Employment of identical oxides for the cathode and anode in a symmetrical solid oxide fuel cell (SSOFC) is beneficial for decreasing the fabrication costs of a robust cell. Ce doping on the A-site in SrFeO3 increased the structural stability in a reducing atmosphere, but ceria was found to exsolve from the perovskite during the cooling process in the air if the doping level reached 20 at. %. The additional doping of 5 at. % Ru in Sr0.8Ce0.2FeO3 on the Fe site could prevent the ceria segregation in air and induce the surface decomposition under fuel conditions for the formation of nanoscale SrO, CeO2 and Ru 0 . The SSOFC with Ce/Ru co-doped SrFeO3 on a Sr-and Mg-doped LaGaO3 (LSGM) electrolyte showed a small Rp value (0.12  cm 2 ) when H2 and the ambient air were used as fuel and oxidant, respectively. The peak power densities of 846 mW cm -2 and 310 mW cm -2 were achieved at 800 o C using H2 and C3H8 as fuel, respectively. The excellent coke resistance of the anode could be related to the simultaneous in situ exsolution of CeO2, SrO and Ru 0 nanoparticles.

With engineering of A-site deficiency and Ti4+/3+ stabilization, Ni0 exsolves and embeds partially in the perovskite under in situ reduction.