2 Molecular design of non-fullerene acceptors (NFAs) is of vital importance for highefficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach as which may introduce undesirable steric hindrance that reduces charge transport in NFAs. Here we show the design and synthesis of a highly efficient NFA family by substituting the beta position of thiophene unit on Y6-based A-DAD-A backbone with branched alkyl chains. It was found that such modification of different alkyl chain length could completely change the molecular packing behavior of NFAs, leading to improved structure order and charge transport in thin films. Unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of branched alkyl chain topology in tuning the molecular packing and blend morphology that leads to improved organic photovoltaic performance.
Lead-free zero-dimensional (0D) organic-inorganic metal halide perovskites have recently attracted increasing attention for their excellent photoluminescence properties and chemical stability.Here,wereport the synthesis and characterization of an air-stable 0D mixed metal halide perovskite (C 8 NH 12 ) 4 Bi 0.57 Sb 0.43 Br 7 ·H 2 O, in whichi ndividual [BiBr 6 ] 3À and [SbBr 6 ] 3À octahedral units are completely isolated and surrounded by the large organic cation C 8 H 12 N + .U pon photoexcitation, the bulk crystals exhibit ultra-broadband emission ranging from 400 to 850 nm, which originates from both free excitons and self-trapped excitons.T his is the first example of 0D perovskites with broadband emission spanning the entire visible spectrum. In addition, (C 8 NH 12 ) 4 Bi 0.57 Sb 0.43 Br 7 ·H 2 Oe xhibits excellent humidity and light stability.T hese findings present an ew direction towards the design of environmentally-friendly,h igh-performance 0D perovskite light emitters.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
Lead‐free halide perovskite nanocrystals (NCs) have drawn wide attention for solving the problem of lead perovskites toxicity and instability. Herein, we synthesize the direct band gap double perovskites undoped and Ag‐doped Cs2NaInCl6 NCs by variable temperature hot injection. The Cs2NaInCl6 NCs have little photoluminescence because of dark self‐trapped excitons (STEs). The dark STEs can be converted into bright STEs by doping with Ag+ to produce a bright yellow emission, with the highest photoluminescence quantum efficiency of 31.1 %. The dark STEs has been directly detected experimentally by ultrafast transient absorption (TA) techniques. The dynamics mechanism is further studied. In addition, the Ag‐doped NCs show better stability than the undoped ones. This result provides a new way to enhance the optical properties of lead‐free perovskites NCs for high‐performance light emitters.
Low-dimensional metal halides have recently attracted extensive attention owing to their unique structure and photoelectric properties.H erein, we report the colloidal synthesis of all-inorganic low-dimensional cesium copper halide nanocrystals (NCs) by adopting ah ot-injection approach.U sing the same reactants and ligands,b ut different reaction temperatures,b oth 1D CsCu 2 I 3 nanorods and 0D Cs 3 Cu 2 I 5 NCs can be prepared. Density functional theory indicates that the reduced dimensionality in 1D CsCu 2 I 3 compared to 0D Cs 3 Cu 2 I 5 makes the excitons more localized, which accounts for the strong emission of 0D Cs 3 Cu 2 I 5 NCs. Subsequent optical characterization reveals that the highly luminescent, strongly Stokes-shifted broadband emission of 0D Cs 3 Cu 2 I 5 NCs arises from the self-trapped excitons.O ur findings not only present am ethod to control the synthesis of low-dimensional cesium copper halide nanocrystals but also highlight the potential of 0D Cs 3 Cu 2 I 5 NCs in optoelectronics. Scheme 1. Colloidal synthesis of cesium copper halide nanocrystals.Supportinginformation and the ORCID identification number for one of the authors of this article can be found under: https://doi.
Thermally activated delayed fluorescence (TADF) is generally observed in solid-state organic molecules or metalorganic complexes. However, TADF in all-inorganic colloidal nanocrystals (NCs) is rare. Herein, we report the first colloidal synthesis of an air-stable all-inorganic lead-free Cs 2 ZrCl 6 perovskite NCs. The Cs 2 ZrCl 6 NCs exhibit long-lived triplet excited state (138.2 ms), and feature high photoluminescence (PL) quantum efficiency (QY = 60.37 %) due to TADF mechanism. The emission color can be easily tuned from blue to green by synthesizing the mixed-halide Cs 2 ZrBr x Cl 6Àx (0 x 1.5) NCs. Femtosecond transient absorption and temperature dependent PL measurements are performed to clarify the emission mechanism. In addition, Bi 3+ ions are successfully doped into Cs 2 ZrCl 6 NCs, which further extends the PL properties. This work not only develops a new lead-free halide perovskite NCs for potential optoelectronic applications, but also offers unique strategies for developing new inorganic phosphors.
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