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.
The electron/hole transport layer plays a very important role in the planar structure of perovskite solar cells. Conjugated polymers have received considerable attention for use in perovskite solar cells as hole/electron transport layers and passivation layers. Although the devices based on conjugated polymer hole transport layers have achieved much progress, their performance is still inferior to that of devices based on the conventional spiro-OMeTAD hole transport layer. Here, we investigated the solvent vapor annealing (SVA) effect on conjugated polymers as well as the corresponding perovskite solar cell devices. It was found that SVA treatment could enhance the hole charge carrier mobility and thin film crystallinity. Meanwhile, the charge transfer efficiency was enhanced, and charge recombination was reduced. Hence, the conjugated polymer based device exhibited comparable or even better performance compared with the conventional spiro-OMeTAD based device. Moreover, the device stability was also improved.
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