TRAP AND RECOMBINATION CENTERS STUDY IN ORGANOLEAD HALIDE PEROVSKITES

摘要

The mechanisms affecting the trapping and recombination processes in thin films of methyl ammonium lead iodide (CH_3NH_3PbI_3) were studied by means of transient photoconductivity measurements and theoretical simulation of the relaxation curves resulting from the photocurrent measurements. In particular there was studied the influence of pressure inside the system of measurement, temperature and intensity of illumination on the photoconductivity response. By using the real part of Fourier transform, the experimental curves of photocurrent rise were analyzed. The analysis revealed that the photocurrent resulting from measurements performed at room temperature under vacuum includes contributions of both band to band photo generation and generation controlled by delayed trap-assisted processes, being the contribution that the first process makes to the intensity of the photocurrent much greater than that of the second one. However if the measurements are done under atmospheric pressure conditions, the photocurrent arise from contributions originated from the same two processes that contributed to the photocurrent obtained under vacuum and a further contribution related with a non delayed trap-assisted process. Studies of the intensity dependence of steady state photocurrent revealed that the processes of generation and recombination in CH_3NH_3PbI_3 films are presented through a combination of monomolecular and bimolecular traps.