25 research outputs found
Identification of Free and Bound Exciton States and Their Phase-Dependent Trapping Behavior in Lead Halide Perovskites
In this work we probe the sub-gap energy states within polycrystalline and
single crystal lead halide perovskites to better understand their intrinsic
photophysics behaviors. Through combined temperature and intensity-dependent
optical measurements, we reveal the existence of both free and bound exciton
contributions within the sub-gap energy state manifold. The trapping and
recombination dynamics of these excitons is shown to be strongly dependent on
the structural phase of the perovskite. The orthorhombic phase exhibits
ultrafast exciton trapping and distinct trap emission, while the tetragonal
phase gives low monomolecular recombination velocity and capture cross-sections
(~10-18 cm2). Within the multiphonon transition scenario, this suppression in
charge trapping is caused by the increase in the charge capture activation
energy due to the reduction in electron-lattice interactions, which can be the
origin for the unexpected long carrier lifetime in these material systems.Comment: 5 figure
Non-Rigid Structure-From-Motion on Degenerate Deformations With Low-Rank Shape Deformation Model
Non-rigid structure-from-motion (NRSfM) is the process of recovering time-varying 3D structures and poses of a deformable object from an uncalibrated monocular video sequence. Currently, most NRSfM algorithms utilize a non-degenerate assumption for non-rigid object deformations whereby the 3D structures of a non-rigid object can be assumed to be a linear combination of basis shapes with full rank three. Unfortunately, this assumption will produce extra degrees-of-freedom when the non-rigid object has some degenerate deformations with shape bases of rank less than three. These extra degrees-of-freedom will yield spurious shape deformations due to non-negligible noise in real applications, which will cause substantial reconstruction errors. To solve this problem, we propose a low-rank shape deformation model to represent 3D structures of degenerate deformations. When modeling degenerate deformations, the proposed model exploits the rank-deficient nature of degenerate deformations in addition to the low-rank property of non-rigid objects' trajectories, thus providing a more accurate and compact representation compared with existing models. Based on this model, we formulate the NRSfM problem as two coherent optimization problems. These problems are solved with iterative non-linear optimization algorithms. Experiments on synthetic and motion capture data are conducted. The results exhibit the significant advantages of our approach over state-of-the-art NRSfM algorithms for the 3D recovery of non-rigid objects with degenerate deformations
Heterojunction interface regulation to realize high-performance flexible Kesterite solar cells
Flexible Cu2ZnSn(S, Se)4 (CZTSSe) solar cells take the advantages of
environmental friendliness, low cost, and multi-scenario applications, and have
drawn extensive attention in recent years. Compared with rigid devices, the
lack of alkali metal elements in the flexible substrate is the main factor
limiting the performance of flexible CZTSSe solar cells. This work proposes a
Rb ion additive strategy to simultaneously regulate the CZTSSe film surface
properties and the CdS chemical bath deposition (CBD) processes. Material and
chemical characterization reveals that Rb ions can passivate the detrimental
Se0 cluster defect and additionally provide a more active surface for the CdS
epitaxial growth. Furthermore, Rb can also coordinate with thiourea (TU) in the
CBD solution and improve the ion-by-ion deposition of the CdS layer. Finally,
the flexible CZTSSe cell fabricated by this strategy has reached a high
total-area efficiency of 12.63% (active-area efficiency of 13.2%), with its VOC
and FF reaching 538 mV and 0.70, respectively. This work enriches the alkali
metal passivation strategies and provides new ideas for further improving
flexible CZTSSe solar cells in the future