Enhanced Light Emission Performance of Mixed Cation Perovskite Films-The Effect of Solution Stoichiometry on Crystallization

The performance of quasi-2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m(-2) and maximum current efficiency of 46.1 cd A(-1), which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m(-2)) and Cs-only (maximum EQE of 4.0%, maximum luminance of 4886 cd m(-2)). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA-only and Cs-only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs(0.5)FA(0.5)PbBr(3) phase (different from cubic FAPbBr(3) and orthorhombic CsPbBr3) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light-emitting performance.

Automated summary

The performance of quasi-2D perovskite light emitting diodes (LEDs) is significantly affected by the ratio of mixed small cations cesium and formamidinium (FA), with the best devices achieved at a Cs:FA ratio of 1:1. This ratio leads to improved photoluminescence quantum yield, enhanced crystallization of the perovskite, and a reduction in trap density, resulting in a substantial improvement in light-emitting performance.