Experimentally Determined Stresses Associated with Elliptical Holes Using Polar Coordinates

Abstract: This paper determines the individual components of stress experimentally in a finite tensile plate containing an elliptical hole using a series representation of an Airy stress function in terms of polar coordinates. The Airy coefficients are evaluated from measured temperature information. As well as satisfying force equilibrium, the thermoelastic results are substantiated independently using strain gages and finite element analysis. Employing real, rather than the commonly used complex, variables can be easier for such problems, avoids inconveniences associated with conformal mapping and the concept is applicable to experimental analysis of arbitrarily shaped and/or loaded cut‐outs.     

Expanded Phase Distribution in Low Average Layer-Number 2D Perovskite Films: Toward Efficient Semitransparent Solar Cells

The application of low average layer-number (〈n〉 ≤ 2) 2D perovskites in semitransparent photovoltaics (ST-PVs) has been hindered by their strong exciton binding energy and high electrical anisotropy. Here, the phase distribution is expanded fully and orderly to enable efficient charge transport in 2D (NMA)₂(MA)Pb₂I₇ (NMA: 1-naphthylmethylammonium, MA: CH₃NH₃⁺) perovskite films by regulating the sedimentation dynamics of organic cation-based colloids. Ammonium chloride is synergistically introduced to enhance the phase separation further and construct a favorable out-of-plane orientation. The wide and graded phase distribution well aligns the energy level to facilitate charge transfer. As a result, the first application of an average 〈n〉 = 2 2D perovskite is implemented in ST-PVs with visible power conversion efficiency (PCE) of 7.52% and high average visible transmittance (AVT) of 40.5%. This study offers a new candidate and an effective strategy for efficient and stable ST-PVs and is relevant to other perovskite optoelectronic devices.     

Mixed Dimensional 2D/3D Hybrid Perovskite Absorbers: The Future of Perovskite Solar Cells?

The cost‐effective processability and high efficiency of the organic–inorganic metal halide perovskite solar cells (PSCs) have shown tremendous potential to intervene positively in the generation of clean energy. However, prior to an industrial scale‐up process, there are certain critical issues such as the lack of stability against over moisture, light, and heat, which have to be resolved. One of the several proposed strategies to improve the stability that has lately emerged is the development of lower‐dimensional (2D) perovskite structures derived from the Ruddlesden–Popper (RP) phases. The excellent stability under ambient conditions shown by 2D RP phase perovskites has made the scalability expectations burgeon since it is one of the most credible paths toward stable PSCs. In this review, the 2D/3D mixed system for photovoltaics (PVs) is elaborately discussed with the focus on the crystal structure, optoelectronic properties, charge carrier dynamics, and their impact on the photovoltaic performances. Finally, some of the further challenges are highlighted while outlining the perspectives of 2D/3D perovskites for high‐efficiency stable solar cells.     

Core/Shell PbSe/PbS QDs TiO2 Heterojunction Solar Cell

Quasi type‐II PbSe/PbS quantum dots (QDs) are employed in a solid state high efficiency QD/TiO₂ heterojunction solar cell. The QDs are deposited using layer‐by‐layer deposition on a half‐micrometer‐thick anatase TiO₂ nanosheet film with (001) exposed facets. Theoretical calculations show that the carriers in PbSe/PbS quasi type‐II QDs are delocalized over the entire core/shell structure, which results in better QD film conductivity compared to PbSe QDs. Moreover, PbS shell permits better stability and facile electron injection from the QDs to the TiO₂ nanosheets. To complete the electrical circuit of the solar cell, a Au film is evaporated as a back contact on top of the QDs. This PbSe/PbS QD/TiO₂ heterojunction solar cell produces a light to electric power conversion efficiency (η) of 4% with short circuit photocurrent (J_sc) of 17.3 mA/cm². This report demonstrates highly efficient core/shell near infrared QDs in a QD/TiO₂ heterojunction solar cell.