Organometal halide perovskite solar cells have evolved in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) reached 20.1% late last year. The key disquiet was stability, which has been limiting practical application, but now the state of the art is promising, being measured in thousands of hours. These improvements have been achieved through the application of different materials, interfaces and device architecture optimizations, especially after the investigation of hole conductor free mesoporous devices incorporating carbon electrodes, which promise stable, low cost and easy device fabrication methods. However, this work is still far from complete. There are various issues associated with the degradation of Omh-perovskite, and the interface and device instability which must be addressed to achieve good reproducibility and long lifetimes for Omh-PSCs with high conversion efficiencies. A comprehensive understanding of these issues is required to achieve breakthroughs in stability and practical outdoor applications of Omh-PSCs. For successful small and large scale applications, besides the improvement of the PCE, the stability of Omh-PSCs has to be improved. The causes of failure and associated mechanisms of device degradation, followed by the origins of degradation, approaches to improve stability, and methods and protocols are discussed in detail and form the main focus of this review article.

Organometal halide perovskite solar cells: degradation and stability

Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials.

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Atomically thin two-dimensional organic-inorganic hybrid perovskites

Two-inch-sized perovskite crystals, CH3 NH3 PbX3 (X=I, Br, Cl), with high crystalline quality are prepared by a solution-grown strategy. The availability of large perovskite crystals is expected to transform its broad applications in photovoltaics, optoelectronics, lasers, photodetectors, LEDs, etc., just as crystalline silicon has done in revolutionizing the modern electronics and photovoltaic industries.

Two-Inch-Sized Perovskite CH3NH3PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization

Hybrid halide perovskites have become the “next big thing” in emerging semiconductor materials, as the past decade witnessed their successful application in high-performance photovoltaics. This resurgence has encompassed enormous and widespread development of the three-dimensional (3D) perovskites, spearheaded by CH3NH3PbI3. The next generation of halide perovskites, however, is characterized by reduced dimensionality perovskites, emphasizing the two-dimensional (2D) perovskite derivatives which expand the field into a more diverse subgroup of semiconducting hybrids that possesses even higher tunability and excellent photophysical properties. In this Perspective, we begin with a historical flashback to early reports before the “perovskite fever”, and we follow this original work to its fruition in the present day, where 2D halide perovskites are in the spotlight of current research, offering characteristics desirable in high-performance optoelectronics. We approach the evolution of 2D halide perovskites f...

Two-Dimensional Hybrid Halide Perovskites: Principles and Promises.

Hybrid perovskites provide the possibility of integrating useful organic and inorganic characteristics within a single crystalline molecular-scale composite, enabling unique electronic, magnetic and optical properties. The ability to understand and control the organic and inorganic structural attributes of these hybrids is important for being able to engineer the physical characteristics, both for fundamental studies as well as potential applications. Recently, a number of new and interesting perovskite structures have been reported and a better understanding has begun to emerge with respect to crystal design considerations. This contribution will review several of these new developments and will provide a more general discussion of structural engineering within this diverse family of compounds.
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Templating and structural engineering in organic–inorganic perovskites

Mineralogical evaluation and industrial applications of the Triassic clay deposits, Southern Tunisia

Phase transitions and crystal dynamics in the cubic perovskite CH3NH3PbCl3

The low-frequency (0 to 500 cm−1) Raman spectra are recorded at different temperatures between 40 and 413 K through the different structural modifications: P21/c P42/ncm Cmca I4/mmm. The results agree with previous NMR data and show that the three higher-temperature tetragonal and orthorhombic phases exhibit specific disorder with respect to the orientation of the methylammonium cation while the monoclinic low-temperature modification is ordered. A soft-mode behaviour is observed in the intermediate P42/ncm and Cmca phases, associated with the high-temperature second-order Cmca I4/mmm transition. A discussion of the unusual phase sequence in these materials is tentatively given, in view of previously proposed mechanisms for the phase transitions.



Les spectres Raman de basse frequence (0 a 500 cm−1) ont ete enregistres a differentes temperatures comprises entre 40 et 413 K, dans les differentes phases cristallines: P21/c P42/ncm Cmca I4/mmm. Les resultats sont en accord avec des donnees RMN anterieures et montrent que les trois phases de plus haute temperature (tetragonales et orthorhombique) presentent un desordre specifique dans l'orientation des cations methylammonium, alors que la phase monoclinique de basse temperature est ordonnee. Un comportement de mode mou est associe a la transition du 2e ordre Cmca I4/mmm de haute temperature observe dans les phases inter-mediaires P42/ncm et Cmca. Une discussion de la sequence de phase inhabituelle de ces materiaux est faite sur la base des mecanismes de transitions de phase proposes anterieurement.

Abdelaziz Daoud

Papers

Mineralogical evaluation and industrial applications of the Triassic clay deposits, Southern Tunisia

Phase transitions and crystal dynamics in the cubic perovskite CH3NH3PbCl3

Low‐frequency raman spectra and phase transitions in perovskite‐type layer compounds. (CH3NH3)2MnCl4 and (CH3NH3)CdCl4

Synthesis, DTA, IR and Raman spectra of penthylenediammonium hexachlorostannate NH3(CH2)5NH3SnCl6.

Vibrational study of hydrogen bonding and structural disorder in Na2H(SO4)2, K3H(SO4)2 and (NH4)3H(SO4)2 crystals