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.

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This paper presents results of a study that allowed identifying states of traps in thin films of hybrid organic-inorganic perovskite compounds based on methylammonium lead halide with different compositions CH3NH3PbX3 (X is Cl, Br or I) prepared by spin-coating, through Thermally Stimulated Current (TSC) measurements. Special emphasis was done in studying the influence of the composition and adsorption of oxygen on the depth of traps and on the density of states associated with trapping centers. Deconvolution of the TSC curves obtained from measurements made inside a vacuum chamber under different oxygen partial pressures, revealed the presence of traps centers whose activation energies are affected by the oxygen concentration. It was also found that TSC peaks do not appear in TSC measurements carried out at pressures less than 0.1 mbar, indicating that the possible nature of the identified traps centers is related to oxygen adsorbed superficially and/or located into the grain boundaries.

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Thin films of CH3NH3PbI3 and (NH2)2CHPbI3 (from now on abbreviated as MAPI and FAPI respectively), with perovskite structure were prepared by sequential evaporation of lead iodide (PbI2) and methylammonium iodide (MAI) or formamidinium iodide (FAI), with special emphasis on the optimization of its optical, morphologic, and structural properties. For this, the evaporation process was automatically controlled with a system developed using virtual instrumentation (VI) that allows electronic control of both evaporation sources temperature and precursors deposition rates, using proportional integral derivative (PID) and pulse width modulation (PWM) control algorithms developed with the LabView software. Using X-ray diffraction (XRD), information was obtained regarding the phase and crystalline structure of the studied samples as well as the effect of the main deposition parameters on crystallite size and microstrain. We also studied the influence of the main deposition parameters on the optical and morphological properties through measurements of spectral transmittance and scanning electron microscopy (SEM) respectively. It was found that the implemented method of sequential evaporation allows preparing, with a high degree of reproducibility, single phase MAPI and FAPI thin films with appropriate properties to be used as active layer in hybrid solar cells. The applicability of MAPI and FAPI thin films as active layer in photovoltaic devices has been demonstrated by using them in solar cells with structure: FTO/ZnO/MAPI(or FAPI)/P3HT/Au.