Halide perovskites have undergone remarkable developments as highly efficient optoelectronic materials for a variety of applications. Several studies indicated the critical role of defects on the performance of perovskite devices. However, the parameters of defects and their interplay with free charge carriers remain unclear. In this study, we explored the dynamics of free holes in methylammonium lead tribromide (MAPbBr3) single crystals using the time-of-flight (ToF) current spectroscopy. By combining ToF spectroscopy and Monte Carlo simulation, three energy states were detected in the bandgap of MAPbBr3. In addition, we found the trapping and detrapping rates of free holes ranging from a few microseconds to hundreds of microseconds. Contrary to previous studies, we revealed a strong detrapping activity of traps. We showed that these traps substantially affect the transport properties of MAPbBr3, including mobility and mobility-lifetime product. Our results provide an insight on charge transport properties of perovskite semiconductors.

A method is presented for the determination of the carrier drift mobility, lifetime, electric field distribution, and the dynamics of space charge formation, including the detrapping energy and capture cross-section of the dominant trap level in polarizing semiconductor radiation detectors. The procedure stems from the laser-induced transient current measurements done at a steady-state and pulsed biasing and at variable temperature. The approach allows us the direct determination of detector parameters from measured data without a complex mathematical treatment. The detrimental effect of surface carrier recombination often hampering the evaluation of detector properties is eliminated. Lifetime worsening caused by the space charge formation is included. The usefulness of the procedure is demonstrated on a CdTe radiation detector.

The interaction of free carriers with defects and some critical defect properties are still unclear in methylammonium lead halide perovskites (MHPs). Here, a multi-method approach is used to quantify and characterize defects in single crystal MAPbI 3 , giving a cross-checked overview of their properties. Time of flight current waveform spectroscopy reveals the interaction of carriers with five shallow and deep defects. Photo-Hall and thermoelectric effect spectroscopy assess the defect density, cross-section, and relative (to the valence band) energy. The detailed reconstruction of free carrier relaxation through Monte Carlo simulation allows for quantifying the lifetime, mobility, and diffusion length of holes and electrons separately. Here, it is demonstrated that the dominant part of defects releases free carriers after trapping; this happens without non-radiative recombination with consequent positive effects on the photoconversion and charge transport properties. On the other hand, shallow traps decrease drift mobility sensibly. The results are the key for the optimization of the charge transport properties and defects in MHP and contribute to the research aiming to improve perovskite stability. This study paves the way for doping and defect control, enhancing the scalability of perovskite devices with large diffusion lengths and lifetimes.

Emerging metal-halide perovskites (MHPs) have shown advanced charge transport properties suitable for application in solar cells, photodetectors, and many more. While the past decade witnessed tremendous progress in MHPs, very little is known about the origin of defects and their effect on carrier lifetime. In this study, we compare hybrid and all-inorganic MHPs prepared by inverse temperature solution and high-temperature melt growth to explore the influence of material preparation on the formation of defects. The presence of a low concentration of vacancies was shown in all MHPs regardless of their synthesis method demonstrated by the interaction of positron particles with vacancies and lattices of MHPs and explained by ab initio simulation of positron annihilation. We combined the Raman, Fourier transform infrared (FTIR), and positron annihilation spectroscopy methods to establish the nature of imperfections in MHPs grown using different methods. Our Raman and FTIR results reveal that only the solution-grown crystals are prone to the incorporation of a solvent in bulk during synthesis. In vast majority of studies, the charge carrier lifetime is explored using photoluminescence (PL) spectroscopy as it is a readily available method. However, PL is very sensitive to both bulk and surface recombination phenomena. Combining current waveform time-of-flight and time-resolved photoluminescence spectroscopy methods, the bulk recombination differs by a factor of 2 from crystals grown by solution versus high-temperature melt. The results propose that solvent trapping matters, not intrinsic defects. The study also suggests potential pathways for further improvement of hybrid and all-inorganic MHPs.

The electron-and hole-transport properties in cadmium zinc telluride selenide (CZTS) crystals are studied using a laser-induced transient-current technique with pulsed and dc bias. The internal electric field profile and velocity of surface recombination are determined by Monte Carlo simulations of electron and hole transient currents combined with a numerical solution of the driftdiffusion equation coupled with Poisson's equation. Electron and hole drift mobilities of μe = 830 cm 2 /Vs and μh = 40 cm 2 /Vs, respectively, are determined. We also develop a simple technique for evaluating surface recombination directly from measured current waveforms without the need for numerical simulation. The good quality of the prepared detector at pulsed bias, with electron-and hole-mobility-lifetime products of (μτ)e = 1.9 × 10 −3 cm 2 /V and (μτ)h = 1.4 × 10 −4 cm 2 /V, respectively, are observed. The formation of a positive space charge, originating from hole injection combined with a recombination level, is found. We observe a significant position dependence of the lifetime of electrons and holes in dc bias due to hole injection. The experiment is successfully fitted by a simple model dominated by a single deep recombination level with an energy of Et = EC − 0.73 eV; concentration of 7.3 × 10 11 cm −3 ; and electron-and hole-capture cross sections of 3.5 × 10 −14 cm 2 and 6.5 × 10 −14 cm 2 , respectively.

Cadmium telluride (CdTe) and its compounds are the materials of choice for producing industrial quality hard x-ray and gamma ray detectors with high spectral resolution and signal-to-noise ratio. However, optimization of the growth process still proves challenging as the yield is small due to inhomogeneities in the material parameters. Here we investigated the influence of inhomogeneous resistivity on charge collection efficiency of CdZnTe radiation detectors operating at high photon fluxes of incoming radiation. We applied a complex of experimental methods-contactless resistivity and photoconductivity mapping, photoluminescence and laser-induced transient current technique. We observed that the charge collection efficiency at low fluxes is nearly independent of resistivity, while at high fluxes the performance of high resistivity part substantially decreases when compared to the lower resistivity part. This behavior is explained by characteristic evolution of defect structure attaining shallow defect self-compensation during the cooling of the solidified crystal. Instabilities at impurity segregation and temperature gradients at the crystal growth cause different concentration of defects that manifest themselves as deep energy levels within the material bandgap. The defect self-compensation is successfully simulated by theoretical model considering defect reactions in tellurium-saturated CdZnTe.

Space charge formation in chromium-compensated GaAs sensors is investigated by the laserinduced transient current technique applying pulsed and DC bias. Formation of non-standard space charge manifested by an appearance of both negatively and positively charged regions in DC biased sensors was revealed during 5 ms after switching bias. Using Monte Carlo simulations of current transients we determined enhanced electron lifetime τ = 150 ns and electron drift mobility μd = 3650 cm 2 /Vs. We developed and successfully applied theoretical model based on fast hole trapping in the system with spatially variable hole conductivity.

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