Two-dimensional perovskite materials attract great attentions for the application of perovskite solar cells (PSCs) due to the regulable bandgap and high stability. However, the power conversion efficiency (PCE) of 2D PSCs is far behind in that of three-dimensional PSCs. Herein, Dion–Jacobson (DJ) phase Pb–Sn perovskite of (PhDMA)MA 4 (Pb 0.5 Sn 0.5 ) 5 I 16 in 2D PSCs is introduced, which has suitable bandgap of 1.27 eV and offers the candidate for the absorber of bottom device in all perovskite tandem solar cells. The nonlinear bandgap behavior of 2D Pb–Sn perovskite materials is certified by adjusting the recipe of precursors to vary the bandgap of perovskite films. Moreover, MACl is employed to improve the film quality of 2D Pb–Sn perovskite, leading to the suppression of the defect density and nonradiative recombination for 2D PSCs. As a result, a high PCE of 12.2% is achieved for DJ phase 2D Pb–Sn PSCs.
Quasi-two-dimensional (quasi-2D) perovskite light-emitting diodes (PeLEDs) are considered as one of the most potential candidates in electroluminescence territory owing to their unique quantum confinement effect and excellent thermal stability of the light. Nevertheless, heterogeneous energy domain distribution leads to severe non-radiative recombination in the process of energy transfer, which enormously hinders the performance and application of PeLEDs. Herein, an ambipolar amino acid, 5-aminovaleric acid (5AVA), is demonstrated to be able to coordinate lead and halides simultaneously with its carboxyl and amidogen groups. The coordinated ambipolar molecule not only reconstitutes energy domains of perovskites but also minimizes the interfacial defects of PeLEDs. Accordingly, the presence of 5AVA in perovskite precursors leads to dramatic suppression of the n = 1 and n = 2 phases and accelerates energy transfer from wide bandgap domains to narrow bandgap ones. As a result, maximum external quantum efficiency (EQE) of 19.3% (18.20% ± 1.10%) is achieved in quasi-2D green PeLEDs with current efficiency of 61.7 cd A −1 .
Hong Lin,Jian Mao,Minchao Qin,Zhilong Song,Wanjian Yin,Xinhui Lu,Wallace C. H. Choy
While red is one of the primary colors for display applications, the investigation of visible red emitting perovskites, particularly 2D perovskites, is relatively limited. In this work, we demonstrate a single-phase Ruddlesden–Popper quasi-2D (C3H7NH3)2CsPb2I7 perovskite for red color LEDs. Through increasing the annealing temperature of (C3H7NH3)2CsPb2I7 perovskite thin films, we have successfully achieved tunable emission wavelengths from 654 to 691 nm. Equally important, for all the quasi-2D perovskite LEDs, once the annealing temperature is fixed, the emission spectrum is independent of bias voltages, which is very important for their use in lighting and displays. With the analysis of the crystallinity, morphology, and thermodynamic stability of the quasi-2D perovskite, we find that the obtained (C3H7NH3)2CsPb2I7 perovskite is a single-phase quasi-2D perovskite with only n = 2 phase. Besides, we found that the red shifting of emission wavelength is caused by the increase of perovskite crystal size while increasing the annealing temperature. Our results also show that the temperature-induced color tunability can be applied to a series of quasi-2D perovskites with different alkylammonium cations. Importantly, we find that short alkylammonium spacers offer better electrical properties for efficient current transport and high performance in LED applications. This work contributes to controlling the optoelectronic properties of quasi-2D perovskites via controlling their crystal growth as well as paves the way to realize practical lighting and display applications of perovskite LEDs.
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