| Abstract [eng] |
In recent years, lead halide perovskites have attracted attention as one of the most promising materials for optoelectronics due to long charge carrier diffusion length, high absorption coefficient, high defect tolerance, tunable bandgap (Eg) and low cost spin-coating deposition technique [1–6]. In 2009, Miyasaka‘s et al. lead perovskite solar cell delivered 3.8 % power conversion efficiency [7], and now, due to rapid development of this technology, efficiency reached 25.7 % value [8]. However, the degradation products of lead-based perovskites can be toxic to the environment and humans, which impedes the commercialization of this technology [9]. Therefore, less toxic lead-free perovskite light absorbers have attracted much attention recently, for example tin halide perovskites which show excellent optoelectronic properties. However, the Sn-based perovskite devices has not exhibited the same rapid development as lead devices, mainly due to facile oxidation process of Sn2+ to Sn4+ and poor power conversion efficiencies, which are defined by fundamental processes happening in the perovskite film. Today many aspects of charge carrier transport are still poorly understood and demand a more in-depth investigation. Thus, for future tin perovskite device stabilization and commercialization it is crucial to fully understand properties of photogenerated carrier transport. The main task of this work is to study charge carrier transport dynamics of formamidine lead iodide perovskites. For this purpose, FAPbxSn1-xI3 (0 ≤ x ≤ 1) films and FASnI3 films with different charge transport layers were produced by spin-coating technique in the inert gas chamber. Research results reveal that in samples with a higher concentration of tin, charge carrier recombination processes are faster due to higher defect density and structural disorder. In addition, tin and lead in partly substituted perovskites form different phases, which also lead to different properties of the charge carrier transport. Also, pure FASnI3 may form two phases with different grain orientation, which affect charge transport differently – in the pump-probe experiment we observed different duration charge relaxation processes in both domains, thus structural disorder may lead to the short charge carrier lifetime. Studies of FASnI3 films with different charge transport layers revealed that charge carriers from perovskite material are most efficiently injected into the PEDOT:PSS hole transfer layer and into the TiO2 electron transfer layer. More efficient injection leads to the higher power conversion efficiencies in solar cells. |
