Spacer Cation Alloying in Ruddlesden-Popper Perovskites for Efficient Red Light-Emitting Diodes with Precisely Tunable Wavelengths.

Jian Qing,Heyong Wang,Tze Chien Sum,Zhan Chen,Feng Gao,Xiao‐Ke Liu,Lintao Hou,Qiang Xu,Sankaran Ramesh,Zhongcheng Yuan

doi:10.1002/adma.202104381

Abstract

Perovskite light-emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure-red (620-660nm) light emission, an essential part for full-color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden-Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge-transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626nm) and deep red (671nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP-based pure-red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure-red or even pure-blue PeLEDs with high performance.

Highlights

Evidence for Spacer Cation AlloyingAccording to the Bragg’s law, the (002) d-spacing of (PBAxMBZA1-x)2PbI4 (x = 1, 0.75, 0.5, 0.25, and 0) are calculated to be 19.8, 18.8, 17.6, 16.2, and 15.0 Å, respectively, showing gradually decreased layer distances from (PBA)2PbI4 to (MBZA)2PbI4
Perovskite light-emitting diodes (PeLEDs) have recently shown significant efficient PeLEDs with high color purity of blue, green, and red are required
According to the Bragg’s law, the (002) d-spacing of (PBAxMBZA1-x)2PbI4 (x = 1, 0.75, 0.5, 0.25, and 0) are calculated to be 19.8, 18.8, 17.6, 16.2, and 15.0 Å, respectively, showing gradually decreased layer distances from (PBA)2PbI4 to (MBZA)2PbI4. These results indicate that PBA and MBZA can mix uniformly to act as co-spacer cations in the alloyed Ruddlesden–Popper perovskites (RPPs)

Summary

Evidence for Spacer Cation Alloying

According to the Bragg’s law, the (002) d-spacing of (PBAxMBZA1-x)2PbI4 (x = 1, 0.75, 0.5, 0.25, and 0) are calculated to be 19.8, 18.8, 17.6, 16.2, and 15.0 Å, respectively, showing gradually decreased layer distances from (PBA)2PbI4 to (MBZA)2PbI4 These results indicate that PBA and MBZA can mix uniformly to act as co-spacer cations in the alloyed RPPs. To affirm the observation of spacer cation alloying, we employ a periodic QW superlattice model for RPP as described in our previous work.[27] The details are given in Supporting Information. Our model accurately fits the exciton resonance energies of the pure (x = 0, 1) as well as the alloyed (x = 0.5) RPP systems (Figure 1c–e), which accounts for the effects of quantum and dielectric confinement.[28] The effective potential barrier heights are extracted, showing gradual increase from x = 1 to x = 0 (Table S1, Supporting Information). The graded values of the potential barrier energy (from model) and Lb (from XRD) imply that in the alloyed film, the barrier layer contains a uniform spacer-cation alloyed composition rather than being composed of discrete pure phases with different barrier widths

Precisely Tunable Photoluminescence upon Spacer Cation Alloying

Device Performance of PeLEDs

General Applicability of Spacer Cation Alloying Approach

Conclusion

Experimental Section

Data Availability Statement