Photon Reabsorption in Mixed CsPbCl$_{3}$:CsPbI$_{3}$ Perovskite Nanocrystal Films for Light-Emitting Diodes

Abstract

Cesium lead halide nanocrystals, CsPbX$_{3}$ (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 CsPbX$_{3}$ (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 CsPbCl$_{3}$ to CsPbI$_{3}$ in solution and within a poly(methyl methacrylate) matrix via photon reabsorption, which also occurs in electrically excited crystals in bulk heterojunction LEDs.N.J.L.K.D. thanks the Cambridge Commonwealth European and International Trust, Cambridge Australian Scholarships, and Charles K. Allen for financial support. M.T. thanks the Gates Cambridge Trust, EPSRC, and the Winton Programme for the Physics of Sustainability for financial support. J.R. thanks the Cambridge Commonwealth European and International Trust, EPSRC and the Winton Programme for the Physics of Sustainability for financial support. E.P.B. thanks the EPSRC Centre for Doctoral Training: New and Sustainable Photovoltaics. R.D.L. thanks the EPSRC for funding. S.M.M. acknowledges competitive research funding from King Abdullah University of Science and Technology (KAUST). F.W.R.R. gratefully thanks financial support from CNPq Grant No. 246050/2012-8. F.W.R.R. and C.D. acknowledge funding from the ERC under Grant No. 259619 PHOTO-EM. C.D. acknowledges financial support from the EU under Grant No. 312483 ESTEEM2. F.D. is thankful for the Herchel Smith fellowship. This work was supported by the EPSRC (Grant Nos. EP/M005143/1, EP/G060738/1, and EP/G037221/1)