Search

Perovskite light-emitting diodes (PeLEDs) based on 3D mixed Br-Cl compositions have shown good color stability and efficiency in the sky-blue color range. However, when the Cl/Br ratio increases to reach deep-blue emission, the performance of the PeLEDs decreases drastically, with the external quantum efficiency (EQE) typically below 1%. Such performance decay is due largely to the poor morphology of the emissive layer. Herein, theoretical and experimental approach is combined to investigate the evolution of solvated lead complexes in the precursor solution of mixed Br-Cl perovskites. It is found that the energetically favorable exchange of halide ions in the lead complexes drives the precipitation of CsCl, leading to extremely low precursor solubility at high Cl/Br ratios and consequently poor perovskite film coverage. Based on the findings, a metastable dissolution strategy for perovskite film preparation is proposed and deep-blue PeLEDs with a record high EQE of 4% in 3D-based PeLEDs and excellent spectral stability is achieved.

A nonuniform vertical phase distribution and thick insulating barrier can decrease the energy transfer between slices in layered perovskite solar cells (PSCs). Herein, an interlayer cross-linked Dion-Jacobson (DJ)-type 2D PSC with 1,4-butanediamine (BDA) as a short-chain insulating spacer [formula: (BDA)MA(n -1)Pb(n)I(3n + 1)] is reported and demonstrates the vertical phase becoming uniform with enhanced exciton coupling, leading to reduced nonradiative recombination. For n = 1 pure phase perovskite, an exciton binding energy of the DJ phase (BDA)PbI4 is approximate to 142 meV, much smaller than approximate to 435 meV of Ruddlesden-Popper (RP) phase (BA)(2)PbI4 (n = 1) perovskite, indicative of exciton-coupling-induced efficient energy transfer. Therefore, the high energy emission peaks for the (BDA)MA(3)Pb(4)I(13) film are not observed even in liquid nitrogen temperature (78 K), which can be distinguished from that of the (BA)(2)MA(3)Pb(4)I(13) film. Energy transfer between 2D slices of (BDA)MA(3)Pb(4)I(13) is 100 times faster than that of (BA)(2)MA(3)Pb(4)I(13). The uniform vertical distribution and exciton coupling mitigate nonradiative energy loss and significantly improve V-oc in inverted structures (PEDOT:PSS/(BDA)MA(3)Pb(4)I(13)/PCBM/bathocuproine/Ag) to approximate to 1.15 V and the control n-butylammonium-based device demonstrates only a V-oc = approximate to 1 V. It is believed that the results would provide a deep understanding of exciton coupling in hybrid multicomponent quantum wells.

Currently, photovoltaic/electroluminescent (PV/EL) perovskite bifunctional devices (PBDs) exhibit poor performance due to defects and interfacial misalignment of the energy band. Interfacial energy-band engineering between the perovskite and hole-transport layer (HTL) is introduced to reduce energy loss, through adding corrosion-free 3,3′-(2,7-dibromo-9H-fluorene-9,9-diyl) bis(n,n-dimethylpropan-1-amine) (FN-Br) into a HTL free of lithium salt. This strategy can turn the n-type surface of perovskite into p-type and thus correct the misalignment to form a well-defined N–I–P heterojunction. The tailored PBD achieves a high PV efficiency of up to 21.54% (certified 20.24%) and 4.3% EL external quantum efficiency. Free of destructive additives, the unencapsulated devices maintain >92% of their initial PV performance for 500 h at maximum power point under standard air mass 1.5G illumination. This strategy can serve as a general guideline to enhance PV and EL performance of perovskite devices while ensuring excellent stability.

Hybrid perovskite thin films are prone to producing surface vacancies during the film formation, which degrade the stability and photovoltaic performance. Passivation via post-treatment can heal these defects, but present methods are slightly destructive to the bulk of 3D perovskite due to the solvent effect, which hinders fabrication reproducibility. Herein, nondestructive surface/interface passivation using 4-fluoroaniline (FAL) is established. FAL is not only an effective antisolvent candidate for surface modification, but also a large dipole molecule (2.84 Debye) with directional field for charge separation. Density functional theory calculation reveals that the nondestructive properties are attributed to both the conjugated amine in aromatic ring and the para-fluoro-substituent. A hot vapor assisted colloidal process is employed for the post-treatment. The molecular passivation yields an ultrathin protection layer with a hydrophobic fluoro-substituent tail and thus enhances the stability and optoelectronic properties. FAL post-treated perovskite solar cell (PSC) delivers a 20.48% power conversion efficiency under ambient conditions. Micro-photoluminescence reveals that passivation activates the dark defective state at the surface and interface, delivering the impact picture of boundary on the local carriers. This work demonstrates a generic nondestructive chemical approach for improving the performance and stability of PSCs.