The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell's performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
Bibliographical noteFunding Information:
This work was supported by the Global Frontier RandD (Research and Development) Program of the Center for Multiscale Energy System (NRF-2011-0031565 and NRF-2016M3A6A7945503) and the Climate Change Program (NRF-2015M1A2A2056542) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (Information and Communication Technology) and Future Planning. This work was also supported by a brand project (1.170003.01) of the Ulsan National Institute of Science and Technology (UNIST) and internal project (no. KK1702-A01) of the Korea Research Institute of Chemical Technology (KRICT). The GIWAXS experiment at the PLS-II 6D UNIST-Pohang Accelerator Laboratory beamline was supported in part by the Ministry of Education, Science, and Technology; Pohang University of Science and Technology; and UNIST-Central Research Facilities Center. We thank Tae Joo Shin for the indexing of 2D GIWAXS patterns. N.J.J. acknowledges financial support from the Basic Science Research Program (NRF-2015R1A6A3A04058164). All results are reported in the main text and supplementary materials. W.S.Y., J.H.N., J.S., and S.I.S. are inventors on patent application (KR 10-2016-0097290) submitted by both UNIST and KRICT that covers the preparation of perovskite films.
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