Abstract
Intrinsic defects in CsPbBr3 microcrystalline films have been studied using thermally stimulated current (TSC) technique in a wide temperature range (100–400 K). Below room temperature, TSC emission is composed by a set of several energy levels, in the range 0.11–0.27 eV, suggesting a quasi-continuum distribution of states with almost constant density. Above room temperature, up to 400 K, the temperature range of interest for solar cells, both dark current and photocurrent, are mainly dominated by energy levels in the range 0.40–0.45 eV. Even if measured trap densities are high, in the range 1013–1016 cm−3, the very small capture cross-sections, about 10−26 m2, agree with the high defect tolerance characterizing this material.
Highlights
The increasing interest of the scientific community on perovskite materials for a wide range of applications as, e.g., solar cells, light-emitting diodes, lasers, photodetectors, is motivated by their favorable properties, such as tunable band gap, strong optical absorption, ambipolar charge transport, and long electron-hole diffusion lengths [1,2,3]
thermally stimulated current (TSC) emission is composed by a set of several energy levels, in the range 0.11–0.27 eV, suggesting a quasi-continuum distribution of states with almost constant density
A picture of a perovskite film deposited on a two-contact printed circuit board (PCB) is shown in Figure 1a, where the gold contacts have a thickness of about 20 μm
Summary
The increasing interest of the scientific community on perovskite materials for a wide range of applications as, e.g., solar cells, light-emitting diodes, lasers, photodetectors, is motivated by their favorable properties, such as tunable band gap, strong optical absorption, ambipolar charge transport, and long electron-hole diffusion lengths [1,2,3]. A direct investigation of electrically active defects in semiconductor material should be performed on the bare semiconductor layer, excluding the other components of the cell This is generally carried out by means of thermal spectroscopy techniques such as deep level transient spectroscopy (DLTS), photo-induced current transient spectroscopy (PICTS), and thermally stimulated current (TSC); being much more sensitive than opto-physical techniques, they are able to detect even very low concentrations of defects [18]. After filling, the temperature is increased with a constant heating rate and the current peak due to electron/hole emission from traps is measured Peak parameters such as maximum temperature, Tmax, peak intensity, Imax, and peak FWHM, can be used to estimate the energy level position in the forbidden gap, Et, the trap capture cross-section, σ, and the concentration of the trap, Nt. TSC is quite useful as it can be applied to any kind of electric field profile settled within the sample, including the ohmic configuration. An accurate TSC analysis should spend efforts in separating possible overlapping components and this is, in general, achieved by cross-correlating results obtained by varying parameters such as heating rate, filling time, filling temperature, e.g., using heating-rate (β-)variation and delayed-heating methods [18]
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