serious concern compared with other commercial solar cells. Moreover, experiments show that PSCs degrade quickly on timescales of minutes when exposed to both light and oxygen. In other words, the decomposition is extremely aggravated under both O 2 atmosphere and light illumination, [3] which becomes an urgent and necessary issue to be solved for employing the PSCs in practical conditions. Misra demonstrated that oxygen prefers to adhere to the perovskite surface by Van der Waals force [4] and causes electron transfer from the perovskite surface to oxygen and form super oxides. [5] The perovskite crystal is decomposed when O 2 binds to vacancies and the PbI bond is broken, drastically leading to the degradation of the perovskite film. [6] When the device is illuminated by ultraviolet (UV) illumination in the O 2 atmosphere, the following degradation process will occur [7] : lights supply energy to oxidate I − to form I 0 and the corresponding free electrons from I − combine with O 2 to form radicals O 2 − , which snatch protons from CH 3 NH 3 + . Then, the volatile CH 3 NH 3 from A site organic cation can easily escape from the perovskite crystal structure. The escaped I − and organic cations lead to the vast collapse of the ABX 3 framework and irreversible degradation of PSCs. Therefore, the harsh condition of both UV light illumination and O 2 atmosphere can extremely expedite the rates of the degradation process.On the other hand, tremendous traps are formed during the solution process and prefer to assemble at grain boundaries (GBs) of the perovskite, leading to the formation of serious nonradiative recombination centers [8] and much more vulnerable perovskite films resisting the invasion of H 2 O and oxygen. Additionally, the grain-boundary defects could supply a shortcut to accelerate ion migration of I − , leading to perovskite phase segregation and device hysteresis issues. [9] Moreover, the pinholes on the surface make direct contraction between the hole transport layer (HTL) and the electron transport layer, inducing detrimental leakage currents in the PSCs. Therefore, dealing with the GB traps is also an essential issue to attain both high PCE and stable stability of the target PSCs. Previous works demonstrate small organic additives such as O-donor 1,3,7-trimethylxanthine, Currently, the photovoltaic performance of perovskite solar cells (PSCs) is closely linked to undermined defects in the perovskite, and the correct approach to ensure stability under practical conditions is still in dispute. Therefore, natural, healthy, and low-cost additives are expected to not only reduce the trap sites but also drastically improve stability. In this work, the natural antioxidant additive lycopene extracted from tomatoes is introduced into PSCs. The results indicate that lycopene can passivate the grain boundaries, improve the crystallinity, reduce trap density, and facilitate the α phase formation of perovskite at room temperature. As a result, the power conversion efficiency (PCE) is considerably improved fr...

Currently, a major challenge for metal-halide perovskite light emitting diodes (LEDs) is to achieve stable and efficient white light emission due to halide ion segregation. Herein, we report a promising method to fabricate white perovskite LEDs using lanthanide (Ln3+) ions doped CsPbCl3 perovskite nanocrystals (PeNCs). First, K+ ions are doped into the lattice to tune the perovskite bandgap by partially substituting Cs+ ions, which are well matched to the transition energy of some Ln3+ ions from the ground state to the excited state, thereby greatly improving the Förster energy transfer efficiency from excitons to Ln3+ ions. Then, creatine phosphate (CP), a phospholipid widely found in organisms, serves as a tightly binding surface-capping multi-functional ligand which regulates the film formation and enhances the optical and electrical properties of PeNC film. Consequently, the Eu3+ doped PeNCs based-white LEDs show a peak luminance of 1678 cd m-2 and a maximum external quantum efficiency (EQE) of 5.4%, demonstrating excellent performance among existing white PeNC LEDs from a single chip. Furthermore, the method of bandgap modulation and the defect passivation were generalized to other Ln3+ ions doped perovskite LEDs and successfully obtained improved electroluminescence (EL). This work demonstrates the comprehensive and universal strategies in the realization of highly efficient and stable white LEDs via single-component Ln3+ ions doped PeNCs, which provides an optimal solution for the development of low-cost and simple white perovskite LEDs.

Lead-free halide double perovskites (DPs) have been proposed as stable and promising alternatives to lead halide perovskites. Understanding the structural–optical properties of halide DPs is important for their applications. In this study, Cs2AgInCl6 DP nanocrystals, with a direct band gap, were synthesized and studied. Because of a strong electron–phonon coupling leading to exciton self-trapping, a broad emission with a large Stokes shift of Cs2AgInCl6 DP nanocrystals is observed. We observed an abnormal blue-shifted emission accompanied by a red-shifted direct absorption edge because of the reduced electron–phonon coupling under compression in the cubic phase Cs2AgInCl6 DP nanocrystals. Our study clarified the basic structural–optical correlation of halide DPs and may promote their application in related fields.