Interface Dipole Management of D-A-Type Molecules for Efficient Perovskite Solar Cells.

Interfacial engineering of perovskite films has been the main strategies in improving the efficiency and stability of perovskite solar cells (PSCs). In this study, three new donor-acceptor (D-A)-type interfacial dipole (DAID) molecules with hole-transporting and different anchoring units are designed and employed in PSCs. The formation of interface dipoles by the DAID molecules on the perovskite film can efficiently modulate the energy level alignment, improve charge extraction, and reduce non-radiative recombination. Among the three DAID molecules, TPA-BAM with amide group exhibits the best chemical and optoelectrical properties, achieving a champion PCE of 25.29% with the enhanced open-circuit voltage of 1.174 V and fill factor of 84.34%, due to the reduced defect density and improved interfacial hole extraction. Meanwhile, the operational stability of the unencapsulated device has been significantly improved. Our study provides a prospect for rationalized screening of interfacial dipole materials for efficient and stable PSCs.

Self-Polymerized Spiro-Type Interfacial Molecule toward Efficient and Stable Perovskite Solar Cells.

In the pursuit of highly efficient perovskite solar cells, spiro-OMeTAD has demonstrated recorded power conversion efficiencies (PCEs), however, the stability issue remains one of the bottlenecks constraining its commercial development. In this study, we successfully synthesize a novel self-polymerized spiro-type interfacial molecule, termed v-spiro. The linearly arranged molecule exhibits stronger intermolecular interactions and higher intrinsic hole mobility compared to spiro-OMeTAD. Importantly, the vinyl groups in v-spiro enable in situ polymerization, forming a polymeric protective layer on the perovskite film surface, which proves highly effective in suppressing moisture degradation and ion migration. Utilizing these advantages, poly-v-spiro-based device achieves an outstanding efficiency of 24.54 %, with an enhanced open-circuit voltage of 1.173 V and a fill factor of 81.11 %, owing to the reduced defect density, energy level alignment and efficient interfacial hole extraction. Furthermore, the operational stability of unencapsulated devices is significantly enhanced, maintaining initial efficiencies above 90 % even after 2000 hours under approximately 60 % humidity or 1250 hours under continuous AM 1.5G sunlight exposure. This work presents a comprehensive approach to achieving both high efficiency and long-term stability in PSCs through innovative interfacial design.

Molecularly Controlled Quantum Well Width Distribution and Optoelectronic Properties in Quasi-2D Perovskite Light-Emitting Diodes.

Owing to their excellent optoelectronic properties, quasi-2D perovskites with self-assembled multiple quantum well (MQW) structures have shown great potential in light-emitting diode (LED) applications. Understanding the correlation between the bulky cation, quantum well assembly, and optoelectronic properties of a quasi-2D perovskite is important. Here, we demonstrate that the dipole moment of the bulky cation can be one of the fundamental factors that controls the distribution and crystallinity of different quantum wells. We find that the bulky cation with a moderate dipole moment leads to moderately distributed well-width MQWs, resulting in a superior device efficiency due to the simultaneous achievement of favorable optical and electronic properties. The peak external quantum efficiency and the maximum luminance of the champion device are 10.8% and 19082 cd m-2, respectively, positioning it among the best-performing quasi-2D green perovskite LEDs without further surface passivation or additive doping. This work provides a perspective on the rational design of bulky cations in quasi-2D perovskite LEDs, which is also essential for the development of other mixed-dimensional perovskite optoelectronic devices.

High-Brightness Perovskite Microcrystalline Light-Emitting Diodes.

Here a high-brightness perovskite microcrystalline light-emitting diode (LED) is reported, in which the perovskite microcrystals were grown directly on the conductive substrate and a simple metal-insulator-semiconductor structure was adopted. A peak external quantum efficiency of 0.46% was obtained, which is high for perovskite microcrystalline LEDs. Importantly, the maximum luminance of the device reaches 8848.4 cd m-2, indicating an ultrahigh brightness of >1.2 × 106 cd m-2 for the microcrystals (corresponding to an ultrahigh current density of 80.9 A cm-2), because the light-emitting area of the microcrystals accounts for only ∼0.7% of the device area. In addition, we have studied the degradation of the device at a high current density by in situ microscopic observation and found that a severe Joule heating effect at large injection is the primary problem to be solved to realize electrically pumped perovskite microcrystal lasing.

Low Roll-Off and High Stable Electroluminescence in Three-Dimensional FAPbI3 Perovskites with Bifunctional-Molecule Additives.

Three-dimensional (3D) perovskites have been demonstrated as an effective strategy to achieve efficient light-emitting diodes (LEDs) at high brightness. However, most 3D perovskite LEDs still suffer from serious efficiency roll-off. Here, using FAPbI3 as a model system, we find that the main reason for efficiency droop and degradation in 3D perovskite LEDs is defects and the ion migration under electrical stress. By introducing bifunctional-molecule 3-chlorobenzylamine additive into the perovskite precursor solution, the detrimental effects can be significantly suppressed through the growth of high crystalline perovskites and defect passivation. This approach leads to bright near-infrared perovskite LEDs with a peak external quantum efficiency of 16.6%, which sustains 80% of its peak value at a high current density of 460 mA cm-2, corresponding to a high brightness of 300 W sr-1 m-2. Moreover, the device exhibits a record half-lifetime of 49 h under a constant current density of 100 mA cm-2.

Efficient and bright warm-white electroluminescence from lead-free metal halides.

Solution-processed metal-halide perovskites are emerging as one of the most promising materials for displays, lighting and energy generation. Currently, the best-performing perovskite optoelectronic devices are based on lead halides and the lead toxicity severely restricts their practical applications. Moreover, efficient white electroluminescence from broadband-emission metal halides remains a challenge. Here we demonstrate efficient and bright lead-free LEDs based on cesium copper halides enabled by introducing an organic additive (Tween, polyethylene glycol sorbitan monooleate) into the precursor solutions. We find the additive can reduce the trap states, enhancing the photoluminescence quantum efficiency of the metal halide films, and increase the surface potential, facilitating the hole injection and transport in the LEDs. Consequently, we achieve warm-white LEDs reaching an external quantum efficiency of 3.1% and a luminance of 1570 cd m-2 at a low voltage of 5.4 V, showing great promise of lead-free metal halides for solution-processed white LED applications.

In Situ-Fabricated Perovskite Nanocrystals for Deep-Blue Light-Emitting Diodes.

Efficient and stable deep-blue emission from perovskite light-emitting diodes (LEDs) is required for their application in lighting and displays. However, this is difficult to achieve due to the phase segregation issue of mixed halide perovskites and the challenge of synthesizing high-quality single-halide deep-blue perovskite nanocrystals through a traditional method. Here, we show that an antisolvent treatment can facilitate the in situ formation of perovskite nanocrystals using a facile spin-coating method. We find that the dropping time of the antisolvent can significantly affect the constitution of nanocrystal perovskite films. With a delay in the start time of the antisolvent treatment, small single-halide perovskite nanocrystals can be achieved, exhibiting efficient deep-blue emission. The LED device shows a stable electroluminescence (EL) peak at 465 nm, with a peak external quantum efficiency and a peak current efficiency of 2.4% and 2.5 cd A-1, respectively. This work provides a facile approach to changing the size of perovskite nanocrystals, thus effectively tuning their EL emission spectra.

Unveiling the synergistic effect of precursor stoichiometry and interfacial reactions for perovskite light-emitting diodes.

Metal halide perovskites are emerging as promising semiconductors for cost-effective and high-performance light-emitting diodes (LEDs). Previous investigations have focused on the optimisation of the emissive perovskite layer, for example, through quantum confinement to enhance the radiative recombination or through defect passivation to decrease non-radiative recombination. However, an in-depth understanding of how the buried charge transport layers affect the perovskite crystallisation, though of critical importance, is currently missing for perovskite LEDs. Here, we reveal synergistic effect of precursor stoichiometry and interfacial reactions for perovskite LEDs, and establish useful guidelines for rational device optimization. We reveal that efficient deprotonation of the undesirable organic cations by a metal oxide interlayer with a high isoelectric point is critical to promote the transition of intermediate phases to highly emissive perovskite films. Combining our findings with effective defect passivation of the active layer, we achieve high-efficiency perovskite LEDs with a maximum external quantum efficiency of 19.6%.