Search

Metal halide perovskites (MHPs) have emerged as promising next-generation optoelectronic materials and achieved remarkable performances in both light-emitting diodes (LEDs) and solar cells (SCs). Despite reaching market demands such as high efficiencies and low manufacturing cost, the long-term stability of MHPs is still a massive challenge for commercialization. The presence of surface and bulk defects due to low-temperature solution-processable methods causes past degradation of perovskites. Here, we have investigated the passivation strategy for methylammonium lead iodide (MAPbI3) using resin polymer poly-[(phenylglycidyl ether)-co-formaldehyde] (PCF). PCF acts as a Lewis base additive with an electron-donating oxygen atom, which can coordinate with undercoordinated Pb2+ ions or NH3+ in perovskite crystals, developing smaller nanocrystalline grains with reduced defects. As a result, the PCF-passivated samples exhibit improved stability against moisture in a humid ambient environment (RH > 70%). Moreover, enhanced photoluminescence (PL) and lifetime were achieved without encapsulation. Furthermore, LEDs are demonstrated using the optimized PCF content. These results show the importance of resin polymers, which performs multiple functionalities such as nanocrystalline grain formation, defect passivation, and stability improvements for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Singlet fission is a process by which an organic semiconductor is able to generate two triplet excitons from a single photon. If charges from the triplets can be successfully harvested without heavy losses in energy, then this process can enable a single‐junction solar cell to surpass the Shockley–Queisser limit. While singlet fission processes are commonly observed in several materials, harvesting the resulting triplets is difficult and has been demonstrated with only a few transport materials. Here, transient absorption spectroscopy is used to investigate singlet fission and carrier transfer processes at the AgBiS2/pentacene (AgBiS2/Pc) heterojunction. The successful transfer of triplets from pentacene to AgBiS2 and the transfer of holes from AgBiS2 to pentacene is observed. Further singlet fission in pentacene by modifying the crystallinity of the pentacene layer and have fabricated the first singlet fission AgBiS2/Pc solar cell is enhanced. Singlet fission devices exhibit higher external quantum efficiency compared with the control devices, and thus demonstrating the significant contribution of charges from the singlet fission process. [ABSTRACT FROM AUTHOR]

Semiconductor nanorods have often been observed to emit polarized light. This property can be useful for emission applications such as displays, optical communications, and biological labeling. Recently, many researchers have tried to replace nanocrystals containing toxic metals, such as Cd or Pb, with alternatives that can also demonstrate polarized emission. Here a low temperature injection (LTI) method with a relatively short chain octylammonium bromide ligand precursor is used to slow down the nanorod formation reaction and the controlled anisotropic growth of Cs3Cu2Br5 nanorods is realized, producing more uniform samples of nanorods with higher aspect ratios than those previously reported. Such nanorods exhibit a very high degree of polarization (DOP) of 0.88 ± 0.04 for single rods, and a corresponding polarization anisotropy of 0.26 for the sample population, both the highest yet reported for any perovskite‐like material. Further this method can be extended to produce Cs3Cu2Cl5 nanorods as well, allowing for broad tuning of their optical properties. [ABSTRACT FROM AUTHOR]

CsPbX3 perovskite nanorods are known to display polarized emission, but also suffer from morphological and spectral instability. Here we synthesized CsPbX3 nanorods with polarized emission across the visible emission spectrum. We find that polarized emission is a function solely of the aspect ratio, as would be expected based on a purely dielectric effect. We then observe changes over time in the emission spectrum and polarization anisotropy as a function of the morphology. We find that, although these perovskite nanorods exhibit strongly polarized emission after synthesis, they suffer from serious morphological instability that reduces the polarization anisotropy over time. Worryingly, nanorods dispersed in anhydrous solvents, and even in a polymer matrix were observed to degrade in both inert environments and under ambient conditions. This results in a significant loss in polarized emission, and represents a problem for many intended applications. Finally, we evaluate several strategies for protecting these particles and find that silica encapsulation can be used to successfully prevent loss of polarized emission even under ambient conditions. [ABSTRACT FROM AUTHOR]

Bromide‐based organo‐metal halide perovskites have shown great potential for use in tandem solar cells (SCs), light‐emitting diodes (LEDs), and photodetectors. Herein, a new protocol using a one‐step deposition method for producing formamidinium lead bromide (FAPbBr3) perovskites is reported, which features a solvent‐engineered intermediate phase to achieve superior films. For the first time, a FABr–PbBr2–DMSO intermediate is identified and single crystals of the same intermediate compound are synthesized. A systematic investigation of phase evolution in the film formation process reveals that DMSO enables crystallization of the FABr–PbBr2–DMSO intermediate and thus modulates the crystallization process of FAPbBr3 perovskite, achieving uniform, smooth films with Volmer–Weber morphology. To prevent hole leakage arising from the larger bandgap of FAPbBr3 than FAPbI3, an additional layer of Mg‐doped ZnO nanoparticles is added. As a result, inverted SCs using these solvent engineered films achieve power conversion efficiencies (PCEs) of up to 9.06%, the highest reported efficiency for inverted FAPbBr3 perovskite devices. [ABSTRACT FROM AUTHOR]

Quantum‐confined CsPbI3 perovskite nanoplatelets (NPLs) are highly desirable for optoelectronic applications owing to their anisotropic electronic properties that substantially boost the light outcoupling efficiency in light‐emitting diodes (LEDs). However, the structural instability of the emissive CsPbI3 phases makes it degrade rapidly to the non‐emissive δ‐phase under ambient conditions. Here, the study presents a synthetic approach to produce spectrally stable CsPbI3 nanoplatelets (NPLs) through solid‐phase crude reactions with metal iodide powders, MI2 (M2+ = Mn2+ or Zn2+). The synthesized NPLs exhibit narrow and color‐pure red emission with high photoluminescence (PL) quantum yields (QYs, ηPL) of up to 85%. Systematic investigations into the surface chemistry of NPLs reveal that metal iodide treatment stabilizes anisotropic CsPbI3 NPLs via surface passivation with metal and halide ions, substantially hindering from the formation of non‐emissive yellow phase. The anisotropic NPLs display signatures of spontaneous self‐assembly in spin‐casted films, which yield strong emission anisotropy, with up to 82% of the transition dipoles being horizontally oriented with respect to the substrate, as revealed by the back focal plane (BFP) imaging. The results presented here shed light on solid‐phase approaches for the preparation of quantum‐confined nanocrystals (NCs) with desirable geometry, which boost the light outcoupling efficiency in LEDs. [ABSTRACT FROM AUTHOR]

PbSe quantum dots (QDs) have stronger electronic coupling resulting from a large Bohr exciton radius, suggesting PbSe QDs may be able to achieve superior charge separation and transport in optoelectronic devices compared with PbS QDs. However, PbS QDs solar cell have achieved a certified 12.01% power conversion efficiency (PCE), whereas PbSe QD photovoltaics lag behind at 8.2% PCE. One reason for this difference is that there has been significantly less work done on surface passivation of PbSe QDs. Here, the surface passivation of chlorinated PbSe QDs is optimized via a halide ion exchange treatment using mixed halide CsPb(Br/I)3 perovskite nanocrystals. Champion devices made from treated QDs achieved a PCE of 9.2%, Voc of 0.56 V, Jsc of 25.7 mA cm−2, and fill factor of 64%. Average PCEs for optimized cells are 8.9%. Detailed physical characterizations including capacitance‐voltage (C‐V), Voc, and Jsc as a function of light intensity, transient photovoltage, and photocurrent measurements are all carried out to investigate the mechanism of the improvement in the PCE and to understand the role of the mixed halide perovskites in providing superior surface passivation for PbSe solar cells. At this time, 9.2% is the highest PCE yet reported for PbSe QDs solar cells. The chloride coated‐PbSe quantum dots are passivated using CsPbX3 (X = Br and I) perovskite quantum dots via halide ion exchange in solution. Solar cells using PbSe quantum dots passivated by CsPbBr0.5I2.5 mixed halide perovskites achieve a 9.2% power conversion, the highest reported efficiency for a PbSe QD device to date. [ABSTRACT FROM AUTHOR]