The past few years, two perovskite materials have attracted much attention in the solar cell community: CH3NH3PbI3 and CH3NH3PbI3–x Cl x . While these materials are usually characterized using their structure (via X-ray diffraction (XRD)) and performance within solar cell communities, not so much attention has been devoted to their surface chemical composition and, specifically, the surface composition. Photoelectron spectroscopy (PES) can easily fulfill this task, and, in addition to chemical information, PES provides an overall picture of the electronic structure of the perovskite and its relation to mesoporous TiO2 when studied with hard X-rays. In this work, CH3NH3PbI3 and CH3NH3PbI3–x Cl x have been compared with each other and also to CH3NH3PbCl3, and it appears that, despite very different morphologies and kinetics of formation, the two former materials present a very similar electronic structure and chemical composition (i.e., no chlorine is observed in the final CH3NH3PbI3–x Cl x materials). Nevertheless, chlorine is very important during the preparation, because it affects the formation of crystalline CH3NH3PbI3. We have also exposed the classical CH3NH3PbI3 to various environments, such as water, temperature, and long-time storage in air and argon, and followed changes of the surface composition with PES. The main result of the different exposures is that the perovskite is decomposed into PbI2, but an important point is that this degradation seems to occur already at 100 °C and is not only related to large humidity. Indeed, even in an inert atmosphere such as argon, a slow degradation to PbI2 is observed. The results obtained are crucial for a better understanding of this material and will help to improve not only the post-conditioning of the cells but also their synthesis.

The electronic structure and chemical composition of efficient CH3NH3PbI3 perovskite solar cell materials deposited onto mesoporous TiO2 were studied using photoelectron spectroscopy with hard X-rays. With this technique, it is possible to directly measure the occupied energy levels of the perovskite as well as the TiO2 buried beneath and thereby determine the energy level matching of the interface. The measurements of the valence levels were in good agreement with simulated density of states, and the investigation gives information on the character of the valence levels. We also show that two different deposition techniques give results indicating similar electronic structures.

Silicon is the second most abundant element on the Earth and one of the more abundant elements in our Solar System. Variations in the relative abundance of the stable isotopes of Si (Si isotope fractionation) in different natural reservoirs, both terrestrial (surface and deep Earth) as well as extra-terrestrial (e.g. meteorites, lunar samples), are a powerful tracer of present and past processes involving abiotic as well as biotic systems. The versatility of the Si isotope tracer is reflected in its wide-ranging applications from understanding the origin of early Solar System objects, planetary differentiation, Moon formation, mantle melting and magma differentiation on the Earth, ancient sea-water composition, to modern-day weathering, clay formation and biological fractionation on land as well as in the oceans. The application of Si isotopes as tracers of natural processes started over six decades ago and its usage has seen a sudden increase over the last decade due to improvements in mass spectrometry, particularly the advent of multicollector inductively coupled plasma mass spectrometers, which has made Si isotope measurements safe and relatively easy while simultaneously improving the accuracy and precision of measurements.

Supramolecular interactions based on porphyrin and fullerene derivatives were successfully adopted to improve the photovoltaic performance of p-type dye-sensitized solar cells (DSCs). Photoelectron spectroscopy (PES) measurements suggest a change in binding configuration of ZnTCPP after co-sensitization with C60PPy, which could be ascribed to supramolecular interaction between ZnTCPP and C60PPy. The performance of the ZnTCPP/C60PPy-based p-type DSC has been increased by a factor of 4 in comparison with the DSC with the ZnTCPP alone. At 560 nm, the IPCE value of DSCs based on ZnTCPP/ C60PPy was a factor of 10 greater than that generated by ZnTCPP-based DSCs. The influence of different electrolytes on charge extraction and electron lifetime was investigated and showed that the enhanced V oc from the Co 21/31 (dtbp) 3 -based device is due to the positive E F shift of NiO. P-type dye-sensitized solar cells (DSCs) 1-10 have attracted intensive interest in the community due to the potential applications in tandem devices 11,12 with n-type DSCs 13 as well as in the artificial photosynthesis systems 14,15 . So far, the highest efficiency of p-type dye-sensitized solar cells is 1.3% obtained by the combination between an organic dye and a cobalt redox couple 16 . In DSCs, the photosensitizer is always one of the crucial components of the devices. To date, some organic as well as inorganic photosensitizers have been developed for p-type DSCs [2][3][4][5]12,[17][18][19][20][21] . In order to improve the photovoltaic properties of p-type DSCs, the recombination process between injected holes in the valence band (VB) of the p-type semiconductor and reduced photosensitizer should be inhibited as much as possible 4 . This problem can be addressed by judicious design of the photosensitizer, including extension of the conjugated system to increase the distance between the electron acceptor unit and the p-type semiconductor surface. This synthetic approach has been shown to provide a longer lifetime of the charge separated state 12,22 . Recently, a porphyrin dye showed a promising device efficiency up to 11%, a comparable efficiency to classic Ru photosensitizers that are ubiquitous in n-type DSC 23. These two points were the main motivations for using porphyrin dyes in p-type DSCs. Lindquist and co-workers adopted the mesotetra(carboxyphenyl) porphyrin (TCPP) for p-type DSCs in 1999 24 . However, at that moment the efficiency of the p-type DSCs based on this porphyrin dye was very unsatisfying, around 0.003%, with the highest incident photon-to-current conversion efficiency (IPCE) value of 0.24% at 540 nm. The poor photovoltaic properties were probably due to the fast hole recombination processes and the quality of the NiO films. Inspired by previous examples of supramolecular interaction between porphyrin and C60 and the fast charge transfer process from porphyrin to C60 derivatives [25][26][27][28][29] , a C60 derivative, N-methyl-2-(49-pyridyl)-3,4-fulleropyrrolidine (C60PPy) was adopted to carry out the formation of the supr...

Direct solar hydrogen generation via a combination of photovoltaics (PV) and water electrolysis can potentially ensure a sustainable energy supply while minimizing greenhouse emissions. The PECSYS project aims at demonstrating a solar‐driven electrochemical hydrogen generation system with an area >10 m2 with high efficiency and at reasonable cost. Thermally integrated PV electrolyzers (ECs) using thin‐film silicon, undoped, and silver‐doped Cu(In,Ga)Se2 and silicon heterojunction PV combined with alkaline electrolysis to form one unit are developed on a prototype level with solar collection areas in the range from 64 to 2600 cm2 with the solar‐to‐hydrogen (StH) efficiency ranging from ≈4 to 13%. Electrical direct coupling of PV modules to a proton exchange membrane EC to test the effects of bifaciality (730 cm2 solar collection area) and to study the long‐term operation under outdoor conditions (10 m2 collection area) is also investigated. In both cases, StH efficiencies exceeding 10% can be maintained over the test periods used. All the StH efficiencies reported are based on measured gas outflow using mass flow meters.