No abstract

All-inorganic CsPbI3 perovskite quantum dots (QDs) have attracted intense attention for their successful application in photovoltaics (PVs) and optoelectronics that are enabled by their superior absorption capability and great photoluminescence (PL) properties. However, their photostability remains a practical bottleneck and further optimization is highly desirable. Here, we studied the photostability of as-obtained colloidal CsPbI3 QDs suspended in hexane. We found that light illumination does induce photodegradation of CsPbI3 QDs. Steady-state spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and transient absorption spectroscopy verified that light illumination leads to detachment of the capping agent, collapse of the CsPbI3 QD surface, and finally aggregation of surface Pb0. Both dangling bonds containing surface and Pb0 serve as trap states causing PL quenching with a dramatic decrease of PL quantum yield. Our work provides a detailed insight about the correlation between the structural and photophysical consequences of the photodegradation process in CsPbI3 QDs and may lead to the optimization of such QDs toward device applications.

A lead-free double-halide perovskite with a well-defined structure was synthesized, likely providing a new candidate material for eco-friendly optoelectronic devices.

We predict an oscillatory bias behavior of the fieldlike spin torque, T ? , in magnetic tunnel junctions, which can be selectively controlled via the asymmetry in band filling between the ferromagnetic leads. This can lead to a linear or quadratic low-bias behavior, including tuning the bias-induced reversal of T ? . These findings reconcile the apparently contradictory experimental results recently reported in the literature. The underlying mechanism for the nonequilibrium interlayer exchange coupling (IEC) of noncollinear configurations is the interplay of four independent IEC for the majority-and minority-spin bands of the leads solely in the ferromagnetic configuration. [3][4][5][6][7] and theoretically [8][9][10][11]. The CIMR offers the promise for making nonvolatile magnetoresistive random access memory devices (MRAM), in which information is written using the STT effect rather than the field-induced magnetic switching.The spin torque can be decomposed into a fieldlike, T ? , and a spin transfer, T k , components both orthogonal to the magnetization of the free ferromagnetic (FM) lead, where the first (latter) are perpendicular (parallel) to the plane of the magnetizations of the left and right FM leads, but with different bias behavior. For example, while recent experiments indicate [5][6][7] that T k reverses sign on changing the current direction, we have recently predicted an anomalous bias behavior, where T k can exhibit a sign reversal without a corresponding sign reversal of the bias or even a quadratic bias dependence [8]. Unlike spin valves, where T ? ( T k , T ? % T k in MTJ, thus playing also an important role in the CIMR [5][6][7].The bias behavior of T ? , directly related to the nonequilibrium interlayer exchange coupling (IEC), remains unresolved and controversial. On the theoretical side, the pioneering work of Slonczewski [1] showed that for symmetric MTJ at zero bias, T ? can change sign with decreasing potential-barrier height. Recent calculations [8,10,12] have predicted a purely quadratic bias dependence of T ? in symmetric MTJ, with d 2 T ? ðVÞ=dV 2 < 0 for any value of band filling (BF) and exchange interaction. On the experimental side, Sankey et al. The purpose of this Letter is to understand the underlying electronic mechanism that controls the bias behavior of T ? , and reconcile the origin of the experimental controversies, without invoking the recently proposed inelastic effects [13]. We predict that T ? oscillates with bias which can be tuned via the MTJ asymmetry. We find an interesting low-bias behavior of IEC, ranging from linear to quadratic bias dependence, with positive or negative bias curvature, including tuning the bias-induced reversal of T ? . We derive a novel general expression relating the bias behavior of T ? in noncollinear MTJ with that of collinear [FM and antiferromagnetic (AFM)] configurations, independent of the details of the electronic structure. We demonstrate that the wide range of bias behavior of IEC in noncollinear MTJ can be understood by the int...