In recent years, rare-earth metals with triply oxidized state, lanthanide ions (Ln3+), have been demonstrated as dopants, which can efficiently improve the optical and electronic properties of metal halide perovskite materials. On the one hand, doping Ln3+ ions can convert near-infrared/ultraviolet light into visible light through the process of up-/down-conversion and then the absorption efficiency of solar spectrum by perovskite solar cells can be significantly increased, leading to high device power conversion efficiency. On the other hand, multi-color light emissions and white light emissions originated from perovskite nanocrystals can be realized via inserting Ln3+ ions into the perovskite crystal lattice, which functioned as quantum cutting. In addition, doping or co-doping Ln3+ ions in perovskite films or devices can effectively facilitate perovskite film growth, tailor the energy band alignment and passivate the defect states, resulting in improved charge carrier transport efficiency or reduced nonradiative recombination. Finally, Ln3+ ions have also been used in the fields of photodetectors and luminescent solar concentrators. These indicate the huge potential of rare-earth metals in improving the perovskite optoelectronic device performances.
Highly luminescent FAPb0.7Sn0.3Br3 nanocrystals with an average photoluminescence (PL) quantum yield of 92% were synthesized by the ligand-assisted reprecipitation method. The 41-nm-thick perovskite film with a smooth surface and strong PL intensity was proven to be a suitable luminescent layer for perovskite light-emitting diodes (PeLEDs). Electrical tests indicate that the double hole-transport layers (HTLs) played an important role in improving the electrical-to-optical conversion efficiency of PeLEDs due to their cascade-like level alignment. The PeLED based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))-diphenylamine)] (TFB)/poly(9-vinylcarbazole) (PVK) double HTLs produced a high external quantum efficiency (EQE) of 9%, which was improved by approximately 10.9 and 5.14 times when compared with single HTL PVK or the TFB device, respectively. The enhancement of the hole transmission capacity by TFB/PVK double HTLs was confirmed by the hole-only device and was responsible for the dramatic EQE improvement.
The electron transport layer (ETL) with excellent charge extraction and transport ability is one of the key components of high-performance perovskite solar cells (PSCs). SnO2 has been considered as a more promising ETL for the future commercialization of PSCs due to its excellent photoelectric properties and easy processing. Herein, we propose a facile and effective ETL modification strategy based on the incorporation of methylenediammonium dichloride (MDACl2) into the SnO2 precursor colloidal solution. The effects of MDACl2 incorporation on charge transport, defect passivation, perovskite crystallization, and PSC performance are systematically investigated. First, the surface defects of the SnO2 film are effectively passivated, resulting in the increased conductivity of the SnO2 film, which is conducive to electron extraction and transport. Second, the MDACl2 modification contributes to the formation of high-quality perovskite films with improved crystallinity and reduced defect density. Furthermore, a more suitable energy level alignment is achieved at the ETL/perovskite interface, which facilitates the charge transport due to the lower energy barrier. Consequently, the MDACl2-modified PSCs exhibit a champion efficiency of 22.30% compared with 19.62% of the control device, and the device stability is also significantly improved.
TiO2 microspheres with particle size of 200–400 nm are embedded in the p–i–n perovskite photodetectors, which are used as light scatterers. This approach was implemented to change the light transfer path in the perovskite layer, which makes the device a higher photon capture ability in a specific incident wavelength range. Compared with pristine device, the photocurrent and responsivity of the device based on such structure are obviously enhanced in the range of 560–610 nm and 730–790 nm. The photocurrent under 590 nm incident light wavelength illumination (light intensity P = 31.42 μW·cm-2) increases from 1.45 μA to 1.71 μA, with an increase of 17.93%, and the responsivity reaches 0.305 A·W-1. In addition, the introduction of TiO2 has no additional negative impact on the carrier extraction and the dark current. And the response time of the device did not deteriorate. Finally, the role of TiO2 as light scatterers is further verified by embedding microspheres into mixed-halide perovskite devices.
Perovskite light-emitting materials possess advantages of high photoluminescence quantum yield (PLQY) and charge carrier mobility, large carrier diffusion length, narrow emission spectrum, easily tunable bandgap, and low preparation costs, leading to the great research enthusiasm in the last decade. However, the research progress of blue perovskite light-emitting diode (LED) is slow, because the synthesis of blue perovskite material is difficult and it is unstable in the air. In this work, blue and green perovskite quantum dots (PQDs) can be obtained by adjusting the growth temperature and ultrasonic time. Photoluminescence (PL) measurements suggest that the luminescence wavelength of PQDs decreases significantly from 528nm to 468nm with increasing the ultrasound time from 4 to 30 min and decreasing the temperature from 2 to -10℃. The reduction of grain size investigated by transmission electron microscopy (TEM) is responsible for the blue-shift of luminous peaks. The perovskite light-emitting diodes (PeLEDs) based on the as-prepared green and blue PQDs have been fabricated. The best performing PeLEDs devices for green and blue light emission showed the maximum external quantum efficiency (EQE) of 6.179% and 0.45%, respectively. This work provides an effective method for the preparation of blue-green PQDs and PeLEDs.
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