A study of trap and recombination centers in MAPbI₃ perovskites

Trapping and recombination processes in thin films of CH₃NH₃PbI₃ (MAPbI₃) 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 MAPbI₃ 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 MAPbI₃ film exhibits a deep trap state at around 459 meV attributed to trap assisted recombination was found; furthermore, the MAPbI₃ films present shallow trap states at 129 and 24 meV that correspond to trap states whose activation process is delayed.