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We present a new Cu(In,Ga)Se2 characterization tool: Cu(In,Ga)Se2 microcells. By creating pixels on a Cu(In,Ga)Se2 substrate, we are able to test electrically different locations. Moreover, because of the reduced size of the cells, (5-to 500-μm wide), heat and spreading resistance losses are made negligible, which make high flux characterizations available. We analyze current-voltage curves under high concentration to gain insight in the physical properties of Cu(In,Ga)Se2 cells. From our analysis, Cu(In,Ga)Se2 electrodeposited absorbers present resistivity fluctuations that are much more important than co-evaporated ones. These absorbers, as they present more electronic defects, are also more affected by the Voc increase under intense fluxes, and the efficiency gains can be very significant: up to 6% absolute efficiency points at less than 50 suns.

Density functional theory (DFT) is applied to analyze ground and excited-state properties of some M(bpy)2L2 complexes (M = Ru, Os, L = CN, SCN, bpy = 2,2‘-bipyridine), both in the gas phase and in aqueous solution. In particular, vertical excitation energies were computed by the PBEO hybrid functional in the framework of a time dependent DFT (TDDFT) approach, whereas the polarizable continuum model (PCM) was used to take into account solvent effects. Our results in the gas phase show that the PBE0 functional provides accurate description of all the low lying electronic states considered and correctly reproduces the excitation spectra of such complexes. Some insights on the difference observed for these complexes in changing the central metal atom, the chemical environment, or the medium are given.

Stability aspects of the Mo/Cu(In,Ga)Se2/CdS/ZnO solar cell are reviewed and assessed. These include (i) the chemical stability of the various interfaces present in the device, (ii) the long-term behavior of metastable defects found in the Cu(In,Ga)Se2 (CIGS) compound, and (iii) the impact of Cu migration on device performance and lifetime. We find that (i) all interfaces within the structure are chemically stable, (ii) metastable defects have a beneficial effect on performance, and (iii) Cu migration effects are reversible and their possible detrimental effects are eclipsed by the beneficial effect of the metastable states. Moreover, Cu out-diffusion from the CIGS layer is absent in photovoltaic-quality CIGS. Finally, we propose a model that explains the exceptional radiation hardness and impurity tolerance of CIGS-based devices, based on the synergetic effect of copper migration and point defect reactions.

We explain the cause for the photocurrent and photovoltage in nanocrystalline, mesoporous dye-sensitized solar cells, in terms of the separation, recombination, and transport of electronic charge as well as in terms of electron energetics. On the basis of available experimental data, we confirm that the basic cause for the photovoltage is the change in the electron concentration in the nanocrystalline electron conductor that results from photoinduced charge injection from the dye. The maximum photovoltage is given by the difference in electron energies between the redox level and the bottom of the electron conductor's conduction band, rather than by any difference in electrical potential in the cell, in the dark. Charge separation occurs because of the energetic and entropic driving forces that exist at the dye/electron conductor interface, with charge transport aided by such driving forces at the electron conductor/contact interface. The mesoporosity and nanocrystallinity of the semiconductor are important not only because of the large amount of dye that can be adsorbed on the system's very large surface, but also for two additional reasons: (1) it allows the semiconductor small particles to become almost totally depleted upon immersion in the electrolyte (allowing for large photovoltages), and (2) the proximity of the electrolyte to all particles makes screening of injected electrons, and thus their transport, possible.

Using atomic layer epitaxy (ALE) which is a soft deposition technique for ZnO it is possible to avoid the deposition of thick buffer layers by chemical bath deposition (CBD) and wet treatments can be almost reduced to surface treatments. In this work new electrochemical and chemical treatments have been designed with the objective of surface passivation and surface doping by using solutions with different reactivities (via pH, complexing agents, metallic cations). ZnO layers are then deposited by ALE to complete the junctions. The results show relations between the interface treatment and the cell characteristics. Efficiencies comparable and in some cases higher than those of the reference cells made with CBD CdS and sputtered ZnO have been obtained (up to 12.7% with indium treatments).

The first stages of the electrochemical deposition of a Cu–In–Se compound on molybdenum-coated glass were investigated. The surface morphology was examined after various deposition times by a field emission gun-scanning electron microscope. The surface composition and chemical environment analysis were characterized by X-ray photoelectron spectroscopy (XPS). Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. This enabled the growth steps to be evidenced. A quasi-instantaneous three-dimensional nucleation occurs. The first nuclei are made of a copper-rich Cu–Se phase without indium. Codeposition of indium starts when the Se/Cu surface ratio reaches a value close to 1, which confirms that the formation of a Cu–Se phase is a prerequisite for indium incorporation. With increasing the deposition time, the In/Cu surface ratio increases and tends to a constant value close to 0.5, smaller than the bulk value. The Se/Cu ratio increases first rapidly and then more slowly, when coalescence of the nuclei has occurred. XPS analysis shows that this two-step behavior corresponds to an evolution of the chemical environment of the Se species, indicating the presence of several Se compounds in the film. X-ray diffraction and Raman spectroscopy confirm the presence of a Cu–Se phase and elemental Se, in addition to the predominant chalcopyrite phase.

The electrochemical behavior of polycrystalline molybdenum thin films in contact with acidic aqueous solutions containing Cu(II), In(III), and Se(IV)species was investigated. The substrate and solutions are used for the electrodeposition of CuInSe2films in the field of photovoltaics. The chemical interaction between Mo electrode and the electrolyte at the initial steps of immersion is studied by in situ electrochemical measurements of the time evolution of the open-circuit potential. Ex situ field emission gun–scanning electron microscope observations for morphological investigations, X-ray photoelectron spectroscopy for surface composition, and chemical environment analysis was carried out. Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. It is shown that molybdenum undergoes electrochemical cementation reactions associated with a characteristic potential increase with immersion time. Immediately after immersion, small nuclei of Cu–Sedeposits appear on the surface, which then grow to form a quasi-continuous layer after 400s. The chemical composition of the layer evolves with immersion time. No indium is incorporated. The global composition changes from a Se∕Cuatomic ratio close to 0.3 to a ratio close to 0.7. The final layer contains at least two phases, i.e., umangite Cu3Se2and CuSe. These complex evolutions are discussed in terms of competing electrochemical reactions and thermodynamic considerations.