Improved device efficiency and lifetime of perovskite light-emitting diodes by size-controlled polyvinylpyrrolidone-capped gold nanoparticles with dipole formation

Abstract

Herein, an unprecedented report is presented on the incorporation of size-dependent gold nanoparticles (AuNPs) with polyvinylpyrrolidone (PVP) capping into a conventional hole transport layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The hole transport layer blocks ion-diffusion/migration in methylammonium-lead-bromide (MAPbBr₃)-based perovskite light-emitting diodes (PeLEDs) as a modified interlayer. The PVP-capped 90 nm AuNP device exhibited a seven-fold increase in efficiency (1.5%) as compared to the device without AuNPs (0.22%), where the device lifetime was also improved by 17-fold. This advancement is ascribed to the far-field scattering of AuNPs, modified work function and carrier trapping/detrapping. The improvement in device lifetime is attributed to PVP-capping of AuNPs which prevents indium diffusion into the perovskite layer and surface ion migration into PEDOT:PSS through the formation of induced electric dipole. The results also indicate that using large AuNPs (> 90 nm) reduces exciton recombination because of the trapping of excess charge carriers due to the large surface area.

Figure 1

Schematic of the device structure with bandgap alignment. (a, b) Schematic of the AuNP-PeLED device structure and band alignment along with thickness of the layers. (c) Extended figures demonstrate the morphology of AuNPs and MAPbBr₃ using UHR FE-SEM. (d, e) Schematic of the inside of the PEDOT:PSS with PVP-capped AuNPs, carrier trapping/detrapping, and WF alignment with and without AuNPs.

Figure 2

Electrical properties and surface morphology. (a) CA analysis with SDIW on the PEDOT:PSS and modified PEDOT:PSS. (b) LT50 measurement from the reference sample to the 100 nm AuNP sample, expressed as normalized based on reference. (c) The XPS analysis about In 3d in all the cases between PEDOT:PSS and AuNP-modified PEDOT:PSS. (d) The time-of-flight-secondary ion mass spectrometry (TOF–SIMS) depth profile of Br⁻ ions. The inset shows a schematic illustration of the depth profiling direction. (e, f) Schematic illustration of In penetration from ITO and surface ion migration of Br⁻ ions from the perovskite layer with/without PVP capping AuNPs.

Figure 3

Device performance of the PeLED devices with and without AuNPs. (a) Current density–voltage–luminance (b) Current efficiency (inset: the trend of current efficiency depending on AuNPs (c) Power efficiency–luminance (d) EQE–luminance plots. (e) The statistical data of current efficiency (f) EL spectra of green PeLEDs with AuNP-modified PEDOT:PSS.

Figure 4

PL and TRPL spectra and optical simulation analysis of AuNP-PeLED. (a, b) Steady-state PL spectra and TRPL result based on the sizes of AuNPs. (c, d) Optical simulation data for the enhancement of out-coupling by AuNPs with different diameters.

Figure 5

Electrical analysis based on the Cole–Cole plot. (a) Schematic of the band diagram and circuit modeling. (b, c) The Cole–Cole plot of AuNP PeLEDs in the condition of low and high voltage, respectively. (d) Injection barrier calculation result based on the hole-only-devices structure with the Richardson–Schottky equation e, 1/τ_eff—current efficiency graph showing the optimal point of AuNP size. The inset is the τ₂—AuNPs size, which shows the size-dependent trend.

Figure 6

Trap-filled limit density analysis of AuNP-modified PEDOT:PSS. (a) J–V curve of the hole-only-device with and without AuNPs. (b–f) Current injection graphs of reference, 10, 50, 90, and 100 nm AuNPs with the schematic illustration of each condition.