RESUMO
We synthesized and characterized methylammonium (MA) mixed tri-halide tin perovskites (MASnIBr2-x Clx ) for carbon-based mesoscopic solar cells free of lead and hole-transporting layers. Varied SnCl2 /SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co-crystallized inside the tin-perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3-y Bry and MASnCl3-z Brz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8 Cl0.2 (SnCl2 =10 %) showed the best photovoltaic performance: JSC =14.0â mA cm-2 , VOC =380â mV, FF=0.573, and PCE=3.1 %, and long-term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8 Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin-based perovskites with average lifetimes less than 100â ps.
RESUMO
The excitonic relaxation dynamics of perovskite adsorbed on mesoporous thin films of Al2O3 and NiO upon excitation at 450â nm were investigated with femtosecond optical gating of photoluminescence (PL) via up-conversion. The temporal profiles of emission observed in spectral region 670-810â nm were described satisfactorily with a composite consecutive kinetic model and three transient components representing one hot and two cold excitonic relaxations. All observed relaxation dynamics depend on the emission wavelength, showing a systematic time-amplitude correlation for all three components. When the NiO film was employed, we observed an extent of relaxation proceeding through the non-emissive surface state larger than through the direct electronic relaxation channel, which quenches the PL intensity more effectively than on the Al2O3 film. We conclude that perovskite is an effective hole carrier in a p-type electrode for NiO-based perovskite solar cells showing great performance.
