Trapping and recombination processes in thin films of CHNHPbI (MAPbI) were studied by means of transient photoconductivity measurements and theoretical simulations of the relaxation curves resulting from the photocurrent measurements; in particular, the influence of temperature as well as of the sample temperature and intensity of illumination and pressure inside the measurement system on the photoconductivity response, were studied. The experimental curves of photocurrent were analyzed using the real part of the Fourier transform. The study revealed that the photocurrent of the MAPbI films, measured at atmospheric pressure, is mainly governed by surface related processes induced by chemisorption and desorption of oxygen, whereas the photocurrent resulting from measurements performed in a vacuum is mainly governed by bulk related processes. It was found that, in general, the photocurrent response is affected by both trap assisted fast recombination processes and traps whose activation process is delayed, with the contribution in the intensity of the photocurrent of the first process being greater that of the second one. Evidence that the MAPbI film exhibits a deep trap state at around 459 meV attributed to trap assisted recombination was found; furthermore, the MAPbI films present shallow trap states at 129 and 24 meV that correspond to trap states whose activation process is delayed.

No abstract

No abstract

Solar cells based on kesterite-type Cu2ZnSnS4 (CZTS) thin films were fabricated using a chemical route to prepare the CZTS films, consisting in sequential deposition of Cu2SnS3 (CTS) and ZnS thin films followed by annealing at 550 • C in nitrogen atmosphere. The CTS compound was prepared in a one-step process using a novel chemical procedure consisting of simultaneous precipitation of Cu2S and SnS2 performed by diffusion membranes assisted CBD (chemical bath deposition) technique. Diffusion membranes were used to optimize the kinetic growth through a moderate control of release of metal ions into the work solution. As the conditions for the formation in one step of the Cu2SnS3 compound have not yet been reported in literature, special emphasis was put on finding the parameters that allow growing the Cu2SnS3 thin films by simultaneous precipitation of Cu2S and SnS2. For that, we propose a methodology that includes numerical solution of the equilibrium equations that were established through a study of the chemical equilibrium of the system SnCl2, Na3C6H5O7·2H2O, CuCl2 and Na2S2O3·5H2O. The formation of thin films of CTS and CZTS free of secondary phases grown with a stoichiometry close to that corresponding to the Cu2SnS3 and Cu2ZnSnS4 phases, was verified through measurements of X-ray diffraction (XRD) and Raman spectroscopy. Solar cell with an efficiency of 4.2%, short circuit current of 16.2 mA/cm 2 and open-circuit voltage of 0.49 V was obtained.

No abstract

No abstract

Thin films of numerous compound semiconductors, which crystallize in a (cubic) sphalerite structure, often display an alternative allotropic form as (hexagonal) wurtzite. The relative proportion of each depends in a characteristic manner on the growth conditions chosen. We applied an external magnetic flux during the growth of cadmium sulfide thin films from a chemical working solution, where the CdS molecules or small clusters are formed by a controlled reaction in an aqueous solution. The incorporation mechanism of such neutral particles into the polycrystalline CdS thin film is supposed to happen in a transition layer via a dissociation into charged constituents close to the growing interface. We found a clear effect of the external magnetic field on the film morphology, when the Lorentz force was acting parallel to the surface plane of the layer. Band-gap energy data from optical absorption measurements suggest dimorphism of the grown films, where the field application turns the commonly cubic crystal modification (Eg = 2.38 eV) into a hexagonal polytype with a 200 meV larger energy gap. PACS Nos.: 81.05Dz, 81.15Lm, 81.15Aa, 81.70Fy, 82.65My, 82.80Ch, 82.80Ej

No abstract