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Abstract:

AbstractCoherent light sources in silicon photonics are the long‐sought Holy Grail because silicon‐based materials have indirect bandgap. Traditional strategies for realizing such sources, e.g., heterogeneous photonic integration, strain engineering, and nonlinear process, are technologically demanding. Here, a hybrid lasing device composed of perovskite nanocrystals and silicon nitride nanobeam cavity is demonstrated. SiN photonic crystal naonobeam cavities are fabricated on a solid substrate with significantly improved thermal and mechanical stabilities compared to conventional suspended ones. In addition, adding a poly (methyl methacrylate) (PMMA)‐encapsulation layer on top of the SiN can significantly boost the Q‐factor of the cavity mode. By dispersing perovskite nanocrystals as emitters in the PMMA layer, high‐performance coherent emissions are obtained in terms of lasing threshold, linewidth, and mode volumes. The work offers a compelling way of creating solution‐processed active integrated photonic devices based on the mature platform of silicon photonics for applications in optical information science and photonic quantum technology.

Abstract:

AbstractThe external quantum efficiencies (EQEs) of perovskite quantum dot light‐emitting diodes (QD‐LEDs) are close to the out‐coupling efficiency limitation. However, these high‐performance QD‐LEDs still suffer from a serious issue of efficiency roll‐off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non‐radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll‐off of 11% at 500 mA cm−2 (the lowest roll‐off known so far) where the EQE is still over 11%.

Abstract:

Perovskite nanocrystal light-emitting devices (PNC LEDs) exhibit great potential in display and lighting applications. Balanced hole and electron injection in the light-emitting layer is undoubtedly an effective way to improve LED performance. Here, bismuth (Bi) was introduced into PNC LEDs to form a silver-bismuth (Ag-Bi) bilayer anode. Ag diffused into a defective 2 nm thick Bi layer to form an alloy-like state that promoted hole injection, reduced the charge transfer resistance, and enhanced charge transfer, leading to more balanced hole-electron carriers in the emission layer through hole injection enhancement. As a result, the turn-on voltage and brightness changed from 2.41 V and 2200 cd m^-2, respectively, for CsPb_1-xZn_xI₃-based LEDs with a Ag monolayer anode to 2.2 V and 3714 cd m^-2, respectively, for devices with a Ag-Bi bilayer anode. In addition, the performance of CsPbI₃ and CsPbBrI₂ PNC-based LEDs has also been effectively improved by using a Ag-Bi bilayer anode.

Abstract:

AbstractControlling the transport and minimizing charge carrier trapping at interfaces is crucial for the performance of various optoelectronic devices. Here, how electronic properties of stable, abundant, and easy‐to‐synthesized carbon dots (CDs) are controlled via the surface chemistry through a chosen ratio of their precursors citric acid and ethylenediamine are demonstrated. This allows to adjust the work function of indium tin oxide (ITO) films over the broad range of 1.57 eV, through deposition of thin CD layers. CD modifiers with abundant amine groups reduce the ITO work function from 4.64 to 3.42 eV, while those with abundant carboxyl groups increase it to 4.99 eV. Using CDs to modify interfaces between metal oxide (SnO2 and ZnO) films and active layers of solar cells and light‐emitting diodes (LEDs) allows to significantly improve their performance. Power conversion efficiency of CH3NH3PbI3 perovskite solar cells increases from 17.3% to 19.5%; the external quantum efficiency of CsPbI3 perovskite quantum dot LEDs increases from 4.8% to 10.3%; and that of CdSe/ZnS quantum dot LEDs increases from 8.1% to 21.9%. As CD films are easily fabricated in air by solution processing, the approach paves the way to a simplified manufacturing of large‐area and low‐cost optoelectronic devices.

Abstract:

Charge extraction by electron transport layers (ETLs) plays a vital role in improving the performance of perovskite solar cells (PSCs). Here, PSCs with four different types of ETLs, such as SnO2, amorphous‐Zn2SnO4 (am‐ZTO), am‐ZTO/SnO2, and SnO2/am‐ZTO, are successfully synthesized. The interface recombination behavior and the charge transport properties of the devices affected by four types of ETLs are systematically investigated. For dual am‐ZTO/SnO2 ETLs, compact am‐ZTO ETL prepared by the pulsed laser deposition method provides a dense physical contact with FTO than the spin coating films, decreasing leakage current and improving charge collection at the interface of ETL/FTO. Moreover, dual am‐ZTO/SnO2 ETLs lead to large free energy difference (ΔG), improving electron injection from perovskite to ETLs. One additional electron pathway from perovskite to am‐ZTO is formed, which can also improve electron injection efficiency. A power conversion efficiency of 20.04% and a stabilized efficiency of 19.17% are achieved for the device based on dual am‐ZTO/SnO2 ETLs. Most importantly, the devices are fabricated at a low temperature of 150 °C, which offers a potential method for large‐scale production of PSCs, and paves the way for the development of flexible PSCs. It is believed that this work provides a strategy to design ETLs via controlling ΔG and interface contact to improve the performance of PSCs.