吴晓晓

Hole-Transporting Layers

In article number 2103807, Lydia Helena Wong and co-workers use Al-doped CuS as a hole transport layer (HTL) for perovskite solar cells. Here, it has been demonstrated that, due to the interaction between sulfur and lead, better perovskite crystallization takes place at the interface. Because of this improved interface quality, the sulfide-HTL based devices outperform the oxide HTL-based devices in terms of ambient stability.

Incorporation of the chromium-based metal–organic framework as an A-site cation allows realizing a new multiple-dimensional electronically coupled CsPbI₂Br perovskite, which is theoretically and experimentally proved to improve the carrier transport ability and stability of perovskite solar cells (PSCs). Consequently, the as-fabricated CsPbI₂Br PSCs demonstrate 17.02% power conversion efficiency while superior long-term stability.

Abstract

Inorganic CsPbI _x Br_{3− x} perovskite solar cells (PSCs) have gained enormous interest due to their excellent thermal stabilities. However, their intrinsically poor moisture stability hampers their further development. Herein, a chromium-based metal–organic framework group is intercalated inside the inorganic PbI framework, resulting in a new multiple-dimensional electronically coupled CsPbI₂Br perovskite. In this structurally and electronically coupled perovskite, the π-conjugated terpyridyl can delocalize the excited valence electrons of metal Cr³⁺ ion, enabling multi-interactive charge-carrier transport channels within CsPbI₂Br perovskites. The stability and efficiency of the produced devices are substantially enhanced in comparison to their counterparts with only a pristine CsPbI₂Br active layer. The optimized all-inorganic PSC yields a power conversion efficiency (PCE) as high as 17.02%. Remarkably, the stabilized device retains 80% of its PCE after 1000 h in the ambient atmosphere. This study provides a new paradigm toward addressing the stability challenge of the inorganic perovskite while enhancing its carrier transport ability.

A novel fullerene molecular template with a solubility enhancer arm (R1) and a π–π interaction inducer arm (R2) is deliberately proposed. This design effort delivers the highest power conversion efficiency over 20% of the device with corresponding fulleropyrrolidine electron transport material for the first time.

Abstract

[6,6]-phenyl-C₆₁-butyric acid methyl ester remains indispensable as the electron transport material (ETM) for perovskite solar cells (PSCs), but its synthesis involves complicated multisteps with low productivity. In contrast, the potential of synthesizing simpler fulleropyrrolidine derivatives has long been overlooked, and little has been understood regarding their structure-dependent effects on photovoltaic (PV) performance. Herein, seven novel fulleropyrrolidine derivatives (F1–F7) are deliberately designed, synthesized, and comprehensively characterized in both solution and thin-film states and subsequently investigated as ETMs for PSCs. Notably, the F4 delivers the highest power conversion efficiencies over 20% of devices, which surpass all reported fulleropyrrolidine ETMs due to its optimal photoelectric property. Moreover, the structure-dependent effects of the fullerenes on PV parameters are uncovered, including solubility, intermolecular interaction, packing structure, and charge-transfer ability, which can guide the future design of high-performance and stable fullerene ETMs for PSCs.

The microscopic mechanism of anion exchange is explored. Besides, a method of using polar solvents to construct in situ exchange channels is proposed. By reducing the energy barrier of anion exfoliation on the surface of perovskite quantum dots, precise control of anion exchange results is achieved, and efficient and stable light-emitting diodes are constructed.

Abstract

Inorganic perovskite quantum dots (QDs) have natural advantages in the field of light-emitting diodes (LEDs) because of their high color purity and tunability in a wide range. However, when manufacturing efficiently mixed-anion perovskite QDs (CsPbBr _x I_{3− x} ) to meet the requirements of the pure red color standard in the display field (≈630 nm), results are difficult to control accurately due to the lack of exploration of its microscopic mechanism. Here, a microdynamics model is constructed for anion exchange dominated by vacancies which revealed the key role of polar solvent in reducing the surface energy barrier of anions through first-principle calculations. Besides, a polar solvent construct in situ anion exchange channels method is proposed. Then, the precise control of anion exchange is demonstrated, and the precise regulation spectrum of the whole red-light range (600–680 nm) is achieved. Finally, various QD LEDs (QLEDs) based on these tunable QDs are fabricated and exhibit excellent photoelectric performance in the main red range (620–680 nm). Among them, the champion QLEDs, have peak external quantum efficiency (EQE) of 16.3% at 633 nm and peak EQE of 18.2% at 646 nm, showing potential in meeting the requirements of display standard.

A poling process that simultaneously modulates the built-in field and interface barriers of the perovskite solar cells has been conducted for the perovskite doped by P(VDF-TrFE). It has been unveiled that the new devices have achieved a high power conversion effectivity of 22.1%, attributed to the piezophototronic effect that effectively enhances the performance of the perovskite solar cell.

As a candidate for next-generation solar devices, perovskite solar cells are increasingly being studied for their rapid increased power conversion efficiency (PCE). One of the possible routes to further increase PCE is the introduction of polarization in the absorption layer which functions as a method for increasing the built-in potential and reducing the interface barrier, leading to much improved carrier separation and extraction. This technique uses the principle of the piezophototronic effect utilized for obtaining enhanced optoelectronic performances. Herein, to introduce internal polarization while maintaining optical absorption performance of the perovskite, organic–inorganic hybrid perovskite composite film solar cells are fabricated by doping polarized polyvinylidenefluoride-co-trifluoroethylene (P(VDF-TrFE)) into the perovskite. The composite film is polarized with an external potential, subsequently inducing the piezophototronic effect to enhance the performances of perovskite solar cells. Experimental results show that this simple polarization method has effectively improved several key characteristics of the solar cell. The PCE has reached up to 22.1%, the short-circuit current (J _sc) increases to 24.2 mA cm⁻², and the open-circuit voltage (V _oc) increases to 1.18 V.

The injection and transport capacity of holes is significantly stronger than electrons in CsSnI₃-based light-emitting diodes; therefore, the charge injection is manipulated by preparing a dendritic CsSnI₃ structure, increasing the interface area of the perovskite/electron-transporter and the probability of radiative recombination. As a result, an efficient device is achieved with a record external quantum efficiency of 5.4%.

Abstract

All-inorganic and lead-free CsSnI₃ is emerging as one of the most promising candidates for near-infrared perovskite light-emitting diodes (NIR Pero-LEDs), which find practical applications including facial recognition, biomedical apparatus, night vision camera, and Light Fidelity. However, in the CsSnI₃-based Pero-LEDs, the holes injection is significantly higher than that of electrons, resulting in unbalanced charge injection, undesired exciton dissipation, and poor device performance. Herein, it is proposed to manage charge injection and recombination behavior by tuning the interface area of perovskite and charge-transporter. A dendritic CsSnI₃ structure is prepared on the hole-transporter, only making a bottom contact with the hole-transporter and exposing all other available crystal surfaces to the electron-transporter. In other words, the interface area of perovskite/electron-transporter is significantly higher than that of perovskite/hole-transporter. Moreover, the embedding interface of perovskite/electron-transporter can spatially confine holes and electrons, increasing the radiation recombination. By taking advantage of the dendritic structure, efficient lead-free NIR Pero-LEDs are achieved with a record external quantum efficiency (EQE) of 5.4%. More importantly, the dendritic structure shows great superiorities in flexible devices, for there is almost no morphology change after 2000-cycles of bends, and the fabricated Pero-LEDs can keep 93.4% of initial EQEs after 50-cycles of bends.

Ferroelectric bubble-like domains, a precursor to electrical skyrmions, arise in epitaxially clamped complex oxide heterostructures. These specially ordered electric dipoles are stable in a freestanding state despite the presence of inhomogeneously distributed structural ripples. This finding opens the door to explore electric skyrmions with arbitrary boundaries and physically flexible topological orders in ferroelectric curvilinear space.

Abstract

Bubble-like domains, typically a precursor to the electrical skyrmions, arise in ultrathin complex oxide ferroelectric–dielectric–ferroelectric heterostructures epitaxially clamped with flat substrates. Here, it is reported that these specially ordered electric dipoles can also be retained in a freestanding state despite the presence of inhomogeneously distributed structural ripples. By probing local piezo and capacitive responses and using atomistic simulations, this study analyzes these ripples, sheds light on how the bubbles are stabilized in the modified electromechanical energy landscape, and discusses the difference in morphology between bubbles in freestanding and as-grown states. These results are anticipated to be the starting point of a new paradigm for the exploration of electric skyrmions with arbitrary boundaries and physically flexible topological orders in ferroelectric curvilinear space.

A low defect halide perovskite film can be fabricated using trimethyl phosphate (TMP). TMP directly forms perovskite without intermediate phase due to weak Lewis basicity. The TMP-based film reduces hysteresis in current-voltage curve of perovskite solar cell. The TMP-based device exhibits better performance (>20%) than other solvent-based ones.

Abstract

Solvent engineering by Lewis-base solvent and anti-solvent is well known for forming uniform and stable perovskite thin films. The perovskite phase crystallizes from an intermediate Lewis-adduct upon annealing-induced crystallization. Herein, it is explored the effects of trimethyl phosphate (TMP), as a novel aprotic Lewis-base solvent with a low donor number for the perovskite film formation and photovoltaic characteristics of perovskite solar cells (PSCs). As compared to dimethylsulfoxide (DMSO) or dimethylformamide (DMF), the usage of TMP directly crystallizes the perovskite phase, i.e., reduces the intermediate phase to a negligible degree, right after the spin-coating, owing to the high miscibility of TMP with the anti-solvent and weak bonding in the Lewis adduct. Interestingly, the PSCs based on methylammonium lead iodide (MAPbI₃) derived from TMP/DMF-mixed solvent exhibit a higher average power conversion efficiency of 19.68% (the best: 20.02%) with a smaller hysteresis in the current-voltage curve, compared to the PSCs that are fabricated using DMSO/DMF-mixed (19.14%) or DMF-only (18.55%) solvents. The superior photovoltaic properties are attributed to the lower defect density of the TMP/DMF-derived perovskite film. The results indicate that a high-performance PSC can be achieved by combining a weak Lewis base with a well-established solvent engineering process.

Herein, the perovskite solar cells with an investor's eye to identify possibilities to lower the entry barrier and capitalize the current level of achievements for their widespread deployment are visited. Perovskite solar cells are analyzed via a 5S criteria, ie., Stability, Safety, Scalability, Sustainability, and Storage, as a tool for analyzing the opportunities and gaps for commercialization.

Perovskite solar cells (PSCs) have received a large amount of research funds due to their potential as a frontrunner in a new generation of solar cells; consequently, the desire to commercialize this technology is mounting. In this roadmap, the knowledge and the technological gaps between laboratory and industry are critically analyzed from the perspective of 5S criteria (Stability, Safety, Sustainability, Scalability, and Storage). To avoid any favoritism in the arguments toward commercializing this technology, herein, the average parameters of PSCs (photoconversion efficiency, durability, cost, manufacturability, and sustainability) estimated from previous studies are analyzed and discussed. Unique opportunities for PSCs in their current stage of achievements are identified, where application-driven, instead of performance-driven, developments are shown to favor their commercialization. Efforts required to improve the average performance of PSCs to state-of-the-art levels are also identified and discussed.