Abstract
Cesium lead halide nanocrystals, CsPbX3 (X = Cl, Br, I), exhibit photoluminescence quantum efficiencies approaching 100% without the core–shell structures usually used in conventional semiconductor nanocrystals. These high photoluminescence efficiencies make these crystals ideal candidates for light-emitting diodes (LEDs). However, because of the large surface area to volume ratio, halogen exchange between perovskite nanocrystals of different compositions occurs rapidly, which is one of the limiting factors for white-light applications requiring a mixture of different crystal compositions to achieve a broad emission spectrum. Here, we use mixtures of chloride and iodide CsPbX3 (X = Cl, I) perovskite nanocrystals where anion exchange is significantly reduced. We investigate samples containing mixtures of perovskite nanocrystals with different compositions and study the resulting optical and electrical interactions. We report excitation transfer from CsPbCl3 to CsPbI3 in solution and within a poly(methyl methacrylate) matrix via photon reabsorption, which also occurs in electrically excited crystals in bulk heterojunction LEDs.
Highlights
Low-cost solution-processable metal halide perovskite semiconductors[1−4] have seen encouraging development as inexpensive absorber layers in solar cells, and show high mobility,[5−7] bright emission,[8] tunable band gap,[9−11] and photon recycling.[12]
We report significantly reduced halide exchange between chloride and iodide in CsPbX3 (X = Cl, I) perovskite nanocrystals because of the unfavorable crystal lattice tolerance factor for iodide−chloride exchange in this system
All processing and characterization were performed in an inert atmosphere. Under these conditions we find that CsPbCl3 and CsPbI3 nanocrystals coexist in solution without undergoing dissolution or significant halogen exchange
Summary
Low-cost solution-processable metal halide perovskite semiconductors[1−4] have seen encouraging development as inexpensive absorber layers in solar cells, and show high mobility,[5−7] bright emission,[8] tunable band gap,[9−11] and photon recycling.[12] Power conversion efficiencies for perovskite solar cells have exceeded 20%.13−16 While the majority of research has focused on thin-film and bulk materials,[4,15,17] perovskite nanocrystals have recently been synthesized These include hybrid organic−inorganic MAPbX3 (MA = methylammonium, X = Cl, Br, I) nanocrystals and nanostructures as well as all-inorganic cesium lead halide CsPbX3 (X = Cl, Br, I). This is the case when crystals with different halide compositions are mixed, resulting in the formation of crystals with an averaged total halide composition.[33,34] Halide exchange has been shown to be possible in both MAPbX3 and CsPbX3 when moving between periodically adjacent halides, for example, from CsPbCl3 to CsPbBr3 and CsPbBr3 to CsPbI3 and vice versa.[33,34]
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