Paulo Ernesto Marchezi

Two-dimensional (2D) chiral metal halide perovskites (CMHPs) emerged as promising materials for spintronics. These 2D semiconductors comprise single layers of corner-sharing metal halide octahedra (n = 1) intercalated by organic cations, which limits charge mobility and spin lifetime. In comparison, quasi-2D analogs, with two or more octahedra layers (n ≥ 2), exhibit higher charge carriers mobility, augmented spin lifetime, and tailorable bandgap. Nonetheless, the few reports on quasi-2D CMHPs in the literature often describe time-consuming synthesis and materials presenting poor chiroptical properties after processing. We address this limitation by designing heterostructure thin films comprising a chiral n = 1 phase with a non-chiral n = 2 phase. Circular dichroism (CD) manifestation in the non-chiral phase confirms chirality transfer in the heterostructures. We found that chirality transfer depends on the intermolecular interaction of the chiral and non-chiral cations, being effective when R-/S-𝛼-methylbenzylammonium (MBA) in the chiral phase is combined with benzylammonium (BZA) in the non-chiral phase. Chirality transfer is weak when n-butylammonium (BA) is used in the non-chiral phase. We attribute this difference to a more effective intermixing enabled by 𝜋-𝜋 stacking in the MBA/BZA heterostructure. This inter-phase chirality transfer strategy opens a new avenue for spintronic materials design.

Incorporating metal-organic complexes into perovskite solar cells (PSCs) can be a suitable strategy to improve device performance via surface defects passivation with further modulation into interfacial charge-carrier dynamics. Moreover, can also enable photophysical processes like metal-to-ligand charge transfer (MLCT) and triplet-triplet annihilation (TTA), sensitizing PSCs active layer and enhancing light harvesting capability. Here, Pt(II)- and Zn(II)-based Salophen and Sal-3,4-ben complexes were employed as interfacial modifiers, with Pt(Sal-3,4-ben) yielding the most significant improvement in photovoltaic performance. Perovskite films incorporating Pt(Sal-3,4-ben) have longer charge-carrier lifetimes, as typical of strong spin-orbit coupling from the heavy Pt center and by TTA-induced charge injection into the perovskite bands. An increase in open-circuit voltage (VOC) (1.07 to 1.12 V) and in short-circuit current density (JSC) (22.18 to 24.31 mA cm-2) is observed together an improvement in fill factor and series resistance reduction. This suggests trap-state passivation and more efficient charge separation/extraction, probably arising from triplet-state processes. Involving excited triplet states may facilitate TTA or delayed fluorescence, indirectly boosting photocurrent generation originated from charge transfer process involving Pt(II) coordination compound and perovskite. In contrast, Zn-based complexes, which lack heavy atoms, exhibit limited triplet-state process resulting in modest improvements, supporting the proposed link between triplet-mediated effects and enhanced JSC. Overall, these results highlight the dual role of metal complexes in both defect passivation and photophysical tuning of PSCs, offering a new platform for exploring triplet-state and singlet-fission engineering toward higher efficiency.

Several studies have demonstrated that low-dimensional structures (e.g., two-dimensional (2D)) associated with three-dimensional (3D) perovskite films enhance the efficiency and stability of perovskite solar cells. Here, we aim to track the formation sites of the 2D phase on top of the 3D perovskite and to establish correlations between molecular stiffness and steric hindrance of the organic cations and their influence on the formation and crystallization of 2D/3D. Using cathodoluminescence combined with a scanning electron microscopy technique, we verified that the formation of the 2D phase occurs preferentially on the grain boundaries of the 3D perovskite. This helps explain some passivation mechanisms conferred by the 2D phase on 3D perovskite films. Furthermore, by employing in situ grazing-incidence wide-angle X-ray scattering, we monitored the formation and crystallization of the 2D/3D perovskite using three cations with varying molecular stiffness. In this series of molecules, the formation and crystallization of the 2D phase are found to be dependent on both steric hindrance around the ammonium group and molecular stiffness. Finally, we employed a 2D/3D perovskite heterointerface in a solar cell. The presence of the 2D phase, particularly those formed from flexible cations, resulted in a maximum power conversion efficiency of 21.5%. This study provides insight into critical aspects related to how bulky organic cations' stiffness and steric hindrance influence the formation, crystallization, and distribution of 2D perovskite phases.

Sputtered nickel oxide (NiO_x) has become one of the most promising inorganic hole transport layers for p–i–n perovskite solar cells (PSCs) due to its appealing features such as its robust nature, low material cost, and easy integration to tandem structures and large‐area applications. However, the main drawback with NiO_x‐based PSCs is typically low open‐circuit voltage (V_OC) due to the inferior energy‐level alignment, low charge mobility, and high recombination at the interface. Herein, two types of phosphonic acid self‐assembled monolayers (SAMs) deposited by blade coating as an interfacial layer to modulate the sputtered NiO_x/perovskite interface properties are used. While sputtered NiO_x serves as a conformally coated hole selective layer, the ultrathin SAM interlayer facilitates the hole extraction and minimizes the energy loss at the interface. Co‐ordinately introduced stabilizing additive, namely octadecyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate (I‐76), further improves the device performance of NiO_x/SAM‐based PSCs, resulting in V_OC of 1.14 V and a power conversion efficiency of 21.8%. By applying these strategies for perovskite module upscaling, aperture area module efficiencies of 19.7%, 17.5%, and 15.5% for perovskite minimodules of 4, 16, and 100 cm² are demonstrated, corresponding to active area module efficiencies of 20.4%, 18.0%, and 16.4%, respectively.

The performance and stability of metal halide perovskite solar cells strongly depend on precursor materials and deposition methods adopted during the perovskite layer preparation. There are often a number of different formation pathways available when preparing perovskite films. Since the precise pathway and intermediary mechanisms affect the resulting properties of the cells, in situ studies have been conducted to unravel the mechanisms involved in the formation and evolution of perovskite phases. These studies contributed to the development of procedures to improve the structural, morphological, and optoelectronic properties of the films and to move beyond spin-coating, with the use of scalable techniques. To explore the performance and degradation of devices, operando studies have been conducted on solar cells subjected to normal operating conditions, or stressed with humidity, high temperatures, and light radiation. This review presents an update of studies conducted in situ using a wide range of structural, imaging, and spectroscopic techniques, involving the formation/degradation of halide perovskites. Operando studies are also addressed, emphasizing the latest degradation results for perovskite solar cells. These works demonstrate the importance of in situ and operando studies to achieve the level of stability required for scale-up and consequent commercial deployment of these cells.

Using in situ photoluminescence measurements during the spin‐coating and annealing steps, this study probes the formation of 2D layers on 3D triple cation perovskite films comparing phenylethylammonium and 2‐thiophenemethylammonium iodide bulky cations. This study elucidates the formation mechanisms of the surface layers for both cases and reveals two regimes during 2D layer formation: a kinetic‐driven and a thermodynamic‐driven process. These driving forces result in different compositions of the 2D/3D interface for each treatment, namely, different ratios of pure 2D (n = 1) and quasi‐2D (n > 1) structures. This study shows that a higher ratio of quasi‐2D phases is more beneficial for device performance, as pure‐2D layers may hamper current extraction. Due to a more evenly distributed formation energy profile among 2D and quasi‐2D phases, highly concentrated 2‐thiophenemethylammonium iodide appears to be more suited for effective surface passivation than its phenylethylammonium analog.

Perovskite solar cells (PSCs) technology is now reaching its full potential in terms of power conversion efficiency, but still presenting problems related to long‐term stability under operating conditions. One of the most promising alternatives to PSCs is the layered PSCs (2D‐PSCs). Layered perovskites present a huge compositional variety, which can be used to directly tune photophysical characteristics that influence the operational mechanisms of the devices. This review addresses the structural organization of both the organic and inorganic sublattices, focusing on how the structure influences the quantum and dielectric confinement, phonons and charge carriers' dynamics, charge mobility, and structural defects. We discuss the relation between the structure‐properties of layered perovskites with the performance of solar cells. We, then, offer insights into how these characteristics have been controlled in the assembly of 2D‐PSCs to improve their efficiency and stability. We conclude by giving a perspective of future developments and open areas of exploration that might impact the progress of this rapidly growing technology. image

In situ GIWAXS experiments reveal that the presence of RGO decreases the formation rate of the perovskite, increases the grain size, and improves the stability of solar cells.