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. 2019 Jun 28;10:2842. doi: 10.1038/s41467-019-10856-z

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 4 — Transient absorption of heterojunction QD films. a Pseudocolor image of transient response for QD heterostructure when photoexciting through the CsPbI₃ layer. For each of the surface plots with dashed contour lines one can visualize the carrier populations at various delay time delays between the pump and probe beam with the model described. Select cuts through the data are presented below the surface plots and offset vertically for clarity. Cuts are shown at 1.48 ps, 153 ps, and 1865 ps time delay. The spectra at each delay can be represented by the bleaching of two Gaussian peaks, one has a center wavelength at 697 nm (red-shaded Gaussian) and is associated with carriers occupying CsPbI₃ while the other peak has a center wavelength at 728 nm (brown-shaded Gaussian) and is associated with carriers spatially occupying the Cs_0.25Fa_0.75PbI₃ component. Vertical lines show the position of the two centered components. b Energy level diagram of the heterostructured film with estimated band alignment from UPS. In experiment a light impinges from the left (CsPbI₃ QDs) while for c light impinges from the right (Cs_0.25FA_0.75PbI₃ QDs). From the alignment, electrons are driven to the FA-containing side with a conduction band offset of 180 meV while holes have a small (20 meV) offset driving holes toward CsPbI₃ c Pseudocolor image of transient response for QD heterostructure when photoexciting through the Cs_0.25FA_0.75PbI₃ layer. The coloring scheme of the decomposed spectra is the same as in a. d, e The decomposed fraction of the TA signal for each delay measured that arises from the CsPbI₃ (red-squares) and Cs_0.25FA_0.75PbI₃ (brown-squares) as a function of time when photoexciting through CsPbI₃ (d) or through Cs_0.25FA_0.75PbI₃ (e). For d, the fraction of CsPbI₃ decreases over time while Cs_0.25FA_0.75PbI₃ increases as electrons are transferred into the FA-containing layer with a charge transfer time average of around 600 ps. For e, the fraction of CsPbI₃ and Cs_0.25FA_0.75PbI₃ is analyzed after the first ps and then stay relatively unchanged. f Pseudocolor image (left) and diagram (right) of a thick single component CsPbI₃ film g Pseudocolor image (right) and diagram (left) of pure Cs_0.25FA_0.75PbI₃