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Additive processing is proven to be an effective method to improve the efficiency and stability of perovskite solar cells; however, its intrinsic role in directing the crystallization pathway and thus morphology formation remains unknown. In situ grazing-incidence wide-angle x-ray scattering (GIWAXS) is applied to study the function of a 1,8-diiodooctane (DIO) additive in manipulating the crystallization behavior of perovskite thin films. It is seen that the DIO additive could induce multi-stage intermediate crystallization phases and increases the activation energy for nucleation and growth, which postpones the perovskite phase transformation time and broadens the transition zone. The elongated crystallization process affords improved perovskite thin film crystallinity and reduces defect density, which enables a longer carrier diffusion length. As a result, improved device efficiency, moisture, and thermal stability can be achieved. The current study provides a new prospective in understanding the additive function in perovskite thin film morphology control from fundamental parameters, indicating the importance of minor processing conditions in global property management toward high device performance.

The performance of polymer:fullerene bulk heterojunction (BHJ) solar cells is significantly influenced by the morphology of electron donor and acceptor blends under the premise that electronic structure is complimentary regarding donor and acceptor materials. There are many cases where intimate mixing of donor and acceptor perturbs the electronic structure, which fundamentally changes the transport and photovoltaic characteristics. Here, we present the bimolecular crystal packing of polymers and fullerenes, and investigate the correlation between device performance and structural details. We find that bimolecular crystallization can reorganize polymer chain packing, leading to poor electron transport and device performance. The size compatibility and the passivation of entropy penalty led to cocrystallization instability, which was clearly seen byin situGIWAXS data. PC61BM is found to intercalate into side chains of PQT by reorganizing both PQT and PC61BM, forming stable, highly ordered bimolecular crystals. The poor electron transport in bimolecular crystal domain could account for the poor device performance in both perovskite and organic solar cells. Bis-PC61BM, on the other hand, only forms loosely packed aggregates in solution, and then rapidly phase separated into large domains with an edge-on interfacial orientation and performed poorly in solar cells.

2D perovskite solar cells with high stability and high efficiency have attracted significant attention. A systematical static and dynamic structure investigation is carried out to show the details of 2D morphology evolution. A dual additive approach is used, where the synergy between an alkali metal cation and a polar solvent leads to high-quality 2D perovskite films with sandwich-type structures and vertical phase segregation. Such novel structure can induce high-quality 2D slab growth and reduce internal and surface defects, resulting in a high device efficiency of 16.48% with enhanced continuous illumination stability and improved moisture (55-60%) and thermal (85 °C) tolerances. Transient absorption spectra reveal the carrier migration from low n to high n species with different kinetics. An [PbI6 ]4- octagon coalescence transformation mechanism coupled with metal and organic cations wrapped is proposed. By solvent vapor annealing, a recrystallization and reorientation of the 2D perovskite slabs occurs to form an ideal structure with improved device performance and stability.

This study reports a blend of [6, 6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) and COi8DFIC non‐fullerene acceptor (NFA) as an electron transport layer (ETL) in perovskite solar cells (PSCs). This mixed small‐molecule ETL showed good inter‐molecule mixing, reduced intermolecular distances and decent morphology, resulting in excellent charge carrier transport properties. Morever, charge carrier extraction and transport at the perovskite/ETL interface was optimized by reducing surface traps and defects due to the passivation ability of various terminal groups from the COi8DFIC molecule. A high power conversion efficiency (PCE) of 19.12 % was achieved by taking advantage of benefits from both molecules, showing much better performance than the invidual PC61BM or COi8DFIC (7.13% for using the NFA only). Moreover, the storage and ambient stabilities of the mixed ETL‐based PSCs increased dramatically compared to control devices. [ABSTRACT FROM AUTHOR]

Dielectric ceramic capacitors have attained considerable attention due to their energy storage performance in the field of advanced high/pulsed power capacitors. For such a purpose, configurationally disordered composite material engineering, with the substitution of suitable oxide cations at a single lattice site have demonstrated a strong dielectric relaxor phase with the ability to show high performance capacitive properties. Herein, two prominent high-entropy ceramics systems (Ba0.2Na0.2K0.2A0.2Bi0.2)TiO3, (with A = La and Mg) were fabricated to evaluate their structural, ferroelectric and dielectric properties. XRD patterns and Rietveld refinement of the XRD analysis confirmed the cubic structure P m 3 ¯ m space group of the ceramics. The relative dielectric analysis of Ba0.2Na0.2K0.2La0.2Bi0.2TiO3 (BNKLBT) and Ba0.2Na0.2K0.2Mg0.2Bi0.2TiO3 (BNKMBT) ceramics were demonstrated with relaxor ferroelectric behavior having diffusion coefficients of 1.617 and 1.753, respectively. Moreover, BNKLBT and BNLMBT ceramics presented better stored energy density (1.062 J/cm3 and 0.8855 J/cm3, respectively) and high energy conversion efficiency (80.27% and 82.38%, respectively) at an electric field of 100 kV/cm. The results clearly demonstrate that such high-entropy configured ceramics have the potential to be used in efficient energy storage devices. [ABSTRACT FROM AUTHOR]

Morphology and miscibility control are still a great challenge in polymer solar cells. Despite physical tools being applied, chemical strategies are still limited and complex. To finely tune blend miscibility to obtain optimized morphology, chemical steric engineering is proposed to systemically investigate its effects on optical and electronic properties, especially on a balance between crystallinity and miscibility. By changing the alkylthiol side chain orientation different steric effects are realized in three different polymers. Surprisingly, the photovoltaic device of the polymerPTBB‐m with middle steric structure affords a better power conversion efficiency, over 12%, compared to those of the polymers PTBB‐o and PTBB‐p with large or small steric structures, which could be attributed to a more balanced blend miscibility without sacrificing charge‐carrier transport. Space charge‐limited current, atomic force microscopy, grazing incidence wide angle X‐ray scattering, and resonant soft X‐ray scattering measurements show that the steric engineering of alkylthiol side chains can have significant impacts on polymer aggregation properties, blend miscibility, and photovoltaic performances. More important, the control of miscibility via the simple chemical approach has preliminarily proved its great potential and will pave a new avenue for optimizing the blend morphology. To finely tune blend miscibility, a novel chemical tool of steric engineering is proposed. It renders a high PCE over 12% for the polymer with middle steric structure, due to a more balanced blend miscibility without sacrificing charge‐carrier transport. Therefore the steric effect‐induced miscibility (SEIM) as a novel chemical strategy exhibits very simple and promising potential in optimizing morphology. [ABSTRACT FROM AUTHOR]