Organo-metal halide perovskites are promising solution-processed semiconductors, however, they possess diverse and largely not understood non-radiative mechanisms. Here, we resolve contributions of individual non-radiative recombination centers (quenchers) in nanocrystals of methylammonium lead iodide by studying their photoluminescence blinking caused by random switching of quenchers between active and passive states. We propose a model to describe the observed reduction of blinking upon cooling and determine energetic barriers of 0.2 to 0.8 eV for enabling the switching process, which points to ion migration as the underlying mechanism. Moreover, due to the strong influence of individual quenchers, the crystals show very individually-shaped photoluminescence enhancement upon cooling, suggesting that the high variety of activation energies of the PL enhancement reported in literature is not related to intrinsic properties but rather to the defect chemistry. Stabilizing the fluctuating quenchers in their passive states thus appears to be a promising strategy for improving the material quality.

Fundmental comprehension of light-induced processes of perovskites are still scarce. One active debate surrounds the influence of excess lead iodide (PbI 2) on device performance, as well as optoelectronic properties, where both beneficial and detrimental traits have been reported. Here, we study its impact on the charge-carrier recombination kinetics by simultaneously acquiring photoluminescence quantum yield and time-resolved photoluminescence as a function of excitation wavelength (450 nm-780 nm). The presence of PbI 2 in the perovskite film is identified via a unique spectroscopic signature in the PLQY spectrum. Probing the recombination in the presence and absence of this signature, we detect a radiative bimolecular recombination mechanism induced by PbI 2. Spatially resolving the photoluminescence, we determine that this radiative process occurs in a small volume at the PbI 2 /perovskite interface, which is only active when charge carriers are generated in PbI 2 , and therefore provide deeper insight into how excess PbI 2 may improve the properties of perovskite based devices.

Metal halide perovskites are an important class of emerging semiconductors. Their charge carrier dynamics is poorly understood due to limited knowledge of defect physics and charge carrier recombination mechanisms. Nevertheless, classical ABC and Shockley-Read-Hall (SRH) models are ubiquitously applied to perovskites without considering their validity. Herein, an advanced technique mapping photoluminescence quantum yield (PLQY) as a function of both the excitation pulse energy and repetition frequency is developed and employed to examine the validity of these models. While ABC and SRH fail to explain the charge dynamics in a broad range of conditions, the addition of Auger recombination and trapping to the SRH model enables a quantitative fitting of PLQY maps and low-power PL decay kinetics, and extracting trap concentrations and efficacies. However, PL kinetics at high power are too fast and cannot be explained. The proposed PLQY mapping technique is ideal for a comprehensive testing of theories and applicable to any semiconductor.

Metal halide perovskites show great promise for a wide range of optoelectronic applications but are plagued by instability when exposed to air and light. This work presents low-temperature solution growth of vertically aligned CsPbBr 3 nanowire arrays in AAO (anodized aluminum oxide) templates with excellent stability, with samples exposed to air for 4 months still exhibiting comparable photoluminescence and UV stability to fresh samples. The single-crystal nanowire length is adjusted from ∼100 nm to 5 μm by adjusting the precursor solution amount and concentration, and we observe length-to-diameter ratios as high as 100. Structural characterization results indicate that large-diameter CsPbBr 3 nanowires have an orthorhombic structure, while the 10 nm- and 20 nm-diameter nanowires adopt a cubic structure. Photoluminescence shows a gradual blue-shift in emission with decreasing nanowire diameter and marginal changes under varying illumination power intensity. The CsPbBr 3 -nanowires/AAO composite exhibits excellent resistance to X-ray radiation and long-term air storage, which makes it promising for future optoelectronic applications such as X-ray scintillators. These results show how physical confinement in AAO can be used to realize CsPbBr 3 nanowire arrays and control their morphology and crystal structure.

layers share a similar bulk heterojunction (BHJ) structure with a well-controlled level of phase separation, consisting of a conjugated polymer as the electron donor and another polymer or small molecule as the electron acceptor. [2] It is worth noting that the micro-and nanostructures of these organic semiconductors, as well as the resulting blend morphology and the subsequent device performance, are extremely sensitive to processing conditions. Such changes in microstructure and morphology naturally occur during the film formation from solution, since the final structure of a BHJ film is determined by the interplay between solutes and solvent, including solubility and miscibility of molecules, solvent evaporation, molecular packing, phase separation, etc. [3] Over the past decades, this has led to the efforts to measure the optical properties of these materials during processing, in order to monitor, understand, and finally manipulate and optimize the film formation process.Several methods are well established to investigate the morphology formation of polymer:fullerene BHJ films. The first attempts to monitor the drying kinetics of BHJ films were done using in situ white-light or laser reflectometry, which can measure the thickness and solid content variation during drying. [4] Later on, spectroscopic ellipsometry was introduced into the in situ studies, allowing the real-time studies of the optical constant, thin-film thickness, surface roughness, optical anisotropy, and compositional change. [5] In the meantime, in situ X-ray scattering and X-ray diffraction were used, either