Incrementally Closing Octagons

The octagon abstract domain is a widely used numeric abstract domain expressing relational information between variables whilst being both computationally efficient and simple to implement. Each element of the domain is a system of constraints where each constraint takes the restricted form ±xi±xj≤c. A key family of operations for the octagon domain are closure algorithms, which check satisfiability and provide a normal form for octagonal constraint systems. We present new quadratic incremental algorithms for closure, strong closure and integer closure and proofs of their correctness. We highlight the benefits and measure the performance of these new algorithms

Deep level trapped defect analysis in CH3NH3PbI3 perovskite solar cells by deep level transient spectroscopy

We report the presence of defects in CH3NH3PbI3, which is one of the main factors that deteriorates the performance of perovskite solar cells. Although the efficiency of the perovskite solar cells has been improved by curing defects using various methods, deeply trapped defects in the perovskite layer have not been systematically studied, and their function is still unclear. The comparison and anal. of defects in differently prepd. perovskite solar cells reveals that both solar cells have two kinds of deep level defects (E1 and E2)​. In the one-​pot soln. processed solar cell, the defect state E1 is dominant, while E2 is the major defect in the solar cell prepd. using the cuboid method. Since the energy level of E1 is higher than that of E2, the cuboid solar cell shows higher open-​circuit voltage and efficiency

Origins of High Performance and Degradation in the Mixed Perovskite Solar Cells

The origins of the high device performance and degradation in the air are the greatest issues for commercialization of perovskite solar cells. Here this study investigates the possible origins of the mixed perovskite cells by monitoring defect states and compositional changes of the perovskite layer over the time. The results of deep-level transient spectroscopy analysis reveal that a newly identified defect formed by Br atoms exists at deep levels of the mixed perovskite film, and its defect state shifts when the film is aged in the air. The change of the defect state is originated from loss of the methylammonium molecules of the perovskite layer, which results in decreased J(SC), deterioration of the power conversion efficiency and long-term stability of perovskite solar cells. The results provide a powerful strategy to diagnose and manage the efficiency and stability of perovskite solar cells

Enhancement of Piezoelectricity in Dimensionally Engineered Metal-Halide Perovskites Induced by Deep Level Defects

Metal halide perovskite solar cells (PSCs) have been considered to be one of the most promising next-generation energy harvesters over the past decades due to remarkably rapid improvement of power conversion efficiency in photovoltaics. However, energy harvesters based on the solar energy source have an intrinsic environment limitation for indoor applications. A feasible solution to the limitation is to add non-solar energy harvesting functions to the solar energy harvesters. Here, the piezoelectric properties of two types of metal halide PSCs are investigated, the 3D only and the 3D/2D structure, showing PCEs of 21.3% and 23.2%, respectively. Piezo-response force microscopy and synchrotron-based X-ray diffraction demonstrate that both types of PSC sample have piezoelectricity. Remarkably, the 3D/2D structure has considerably higher piezoelectric amplitude than the 3D-only. The deep level transient spectroscopy results reveal that the enhancement in the piezoelectricity of the 3D/2D structure originates from Pb-Br defects. This study unravels the role of defects in the piezoelectricity of metal halide PSCs and provides a direction to develop the multi-function energy harvesters based on the PSCs

Microscopic Analysis of Inherent Void Passivation in Perovskite Solar Cells

The presence of voids in perovskite solar cells influences the efficiency because of accelerated charge recombination. The induced electric field near voids due to band bending attracts photogenerated electrons and holes toward the voids, leading to carrier recombination. However, if the surface of the voids is coated by materials with a band gap higher than that of the perovskite layer, the strong electric field induced near the voids in the opposite way prevents carriers from recombining. We identified voids in the perovskite layer by using an electron beam-induced current technique and found the influence of field-assisted passivation by organic materials on the efficiency of the solar cell