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Towards Efficient and Stable Perovskite Light-Emitting Diodes

Periodic Reporting for period 1 - PeLED (Towards Efficient and Stable Perovskite Light-Emitting Diodes)

Reporting period: 2018-07-01 to 2020-06-30

Global energy consumption is increasing rapidly nowadays. Considering that displays and lighting accounts for a substantial proportion of energy consumption, efficient light-emitting diodes (LEDs) would play an important role in reducing energy consumption globally. Recently, perovskite materials have emerged as promising candidates for high-performance and low-cost LEDs. They have outstanding optoelectronic properties and solution processability. Since the first room-temperature perovskite LEDs demonstrated in 2014, rapid progress has been made through interfacial engineering and nanocrystal pinning techniques. However, the poor stability and relatively low photoluminescent efficiency of the perovskite materials are still two major problems that limit further advances of this promising technology. This project aims to address these problems and to develop efficient and stable perovskite LEDs through design and synthesis of new perovskite emitters, deposition of high-quality perovskite films and fabrication of high-performance LED devices. During this reporting period, we have designed and synthesized a series of new perovskite emitters, including Ruddlesden-Popper perovskites and perovskite-molecule composites. We have also developed a new approach for depositing high-quality Ruddlesden-Popper perovskite thin films directly from commercially available amines. Moreover, we have achieved efficient and stable perovskite LEDs with an external quantum efficiency of 17.3% and a long lifetime of 100 h (measured at an initial radiance of 15 W sr-1 m-2). These results represent significant breakthroughs in achieving perovskite LEDs with both high efficiency and long lifetime.
To reach the objectives of this project:

(a) We have design and synthesized a series of efficient and stable Ruddlesden-Popper perovskite emitters by optimizing the organic spacer cations and employing impurity doping. We replaced the commonly used phenylethylammonium cation with novel bulk organic cations and studied their structure-property relationship. Furthermore, we have enhanced the properties of -based Ruddlesden-Popper perovskite emitters through Mn-doping, resulting in the first yellow LEDs based on Ruddlesden-Popper perovskite emitters. Moreover, we have found that the addition of organic amines could lead to the formation of high-quality three-dimensional perovskites embedding in molecular matrix rather than Ruddlesden-Popper perovskites, forming perovskite-molecule composite thin films. Based on such new thin films, we have developed perovskite LEDs with both high efficiency and long lifetime.

(b) We have obtained a series of high-quality Ruddlesden-Popper perovskite thin films by controlling the crystallization processes and surface defects passivation. Moreover, we have developed a new approach to prepare high-quality Ruddlesden-Popper perovskite thin films directly from organic amines.

(c) We have fabricated a wide range of efficient and stable perovskite LEDs based on n-i-p and p-i-n architectures. Among them, a perovskite LED with a high external quantum efficiency of 17.3% and long half lifetime of 100 h (measured at initial radiance of 15 W sr−1 m−2) was obtained. Furthermore, we have carried out device physics studies on this perovskite LED and found that the device degradation of our PeLED is mainly dominated by the degradation of the emissive layer at relative low voltages, whereas the degradation of the interfaces between the emissive layer and the charge-transport layers could be dominant at relative high voltages.

The results generated through this project have been disseminated in scientific journals and national and international conferences/workshops, and communicated to wider communities through press releases and social media.
The results generated through this project represent significant breakthroughs in the research field of perovskite LEDs, including novel perovskite materials and devices as well as new approaches and insights:

(a) New materials: we have obtained a number of new Ruddlesden-Popper perovskite emitters and a new type of perovskite material, that is, perovskite-molecule composite. These results have been published in peer-reviewed papers, The Journal of Physical Chemistry Letters 2019, 10 (11), 3171-3175 and Nature Communications, 2020, 11, 891. The achievements of these new materials and the understanding of their structure-property relationships will spur new developments of perovskite materials for high-performance LEDs.

(b) New devices: we have obtained perovskite LEDs with both high efficiency and long half lifetime, which delivered a high external quantum efficiency of 17.3% and long half lifetime of 100 h measured at initial radiance of 15 W sr−1 m−2. These results have been published in Nature Communications, 2020, 11, 891.

(c) New approaches: we have developed a new approach to prepare high-quality Ruddlesden-Popper perovskite thin films directly from organic amines, which has been published in a peer-reviewed paper Advanced Materials, 2019, 31, 1904243. This approach not only represents a new pathway to fabricate efficient devices based on Ruddlesden-Popper perovskite thin films, but also provides an effective method to screen new organic spacers with further improved performance. Moreover, this approach can be used in other perovskite optoelectronic devices such as solar cells, photodetectors, and so on.

(d) New insights: we have found that the degradation mechanism of perovskite LEDs strongly depends on the driving voltage, which should draw more attention. The results, which have been published in Nature Communications, 2020, 11, 891, pave the way for achieving highly stable perovskite LEDs.