Volume 3, Issue 2, Pages 290-302 (August 2017) A Bifunctional Lewis Base Additive for Microscopic Homogeneity in Perovskite Solar Cells  Jin-Wook Lee, Sang-Hoon Bae, Yao-Tsung Hsieh, Nicholas De Marco, Mingkui Wang, Pengyu Sun, Yang Yang  Chem  Volume 3, Issue 2, Pages 290-302 (August 2017) DOI: 10.1016/j.chempr.2017.05.020 Copyright © 2017 Elsevier Inc. Terms and Conditions

Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 MAPbI3 Film via the Adduct Approach with and without Urea (A) Schematics showing the formation of the perovskite layer with and without urea. (B) The films without (upper) and with 1 mmol of urea (lower) as a function of heat-treatment temperature and time. (C) Fourier transform infrared (FTIR) spectra of MAI⋅PbI2⋅DMSO adduct, urea, MAI⋅PbI2⋅DMSO⋅urea, and MAI⋅PbI2⋅urea adduct powder. (D) The magnified FTIR spectra showing the fingerprint region for C=O and S=O stretch. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Effect of Addition of Urea on Photovoltaic Performance (A) Photovoltaic parameters of MAPbI3 perovskite solar cells as a function of the amount of urea: short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), and power conversion efficiency (PCE). (B and C) Current density-voltage (J-V) curves (B) and external quantum efficiency (EQE) spectra (C) of the best-performing device with and without 4 mol % urea. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 FTIR and XRD Spectra without and with Urea (A) Fourier transform infrared (FTIR) spectra of urea (powder), MAPbI3 (film), and MAPbI3 with 4 mol % urea (film). (B) The fingerprint region for C=O stretch (black arrows), N–H bend (red arrows), and C–N stretch (blue arrows). (C) X-ray diffraction patterns of urea (powder) and perovskite film without and with 4 mol % urea. Peaks indexed with ∗ and # originate from PbI2 and ITO, respectively. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Effect of the Addition of Urea on the Morphology of MAPbI3 Atomic force microscopy (AFM) images of (A) bare MAPbI3 and (B) MAPbI3 with 4 mol % urea on SnO2-coated ITO substrates. Cross-sectional scanning electron microscopy (SEM) images of perovskite solar cells based on (C) bare MAPbI3 and (D) MAPbI3 with 4 mol % urea. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 5 Absorption and Fluorescence Data with and without Urea (A–C) UV-visible absorption (A), steady-state photoluminescence (PL) (B), and time-resolved PL decay profiles (C) of MAPbI3 film without and with 4 mol % urea. The films were deposited on a glass substrate. Inset in (C): magnified spectra showing the initial decay profile. Empty circles and solid lines indicate measured data and fitted curves, respectively. (D) Schematics showing film crystallization and corresponding charge transporting characteristics. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 6 Admittance Spectroscopy and Elemental Distribution Mapping (A and B) Frequency-capacitance (f-C) (A) and trap density curves (B) measured from perovskite solar cells without and with 4 mol % urea. Inset in (A) shows the Mott-Schottky plot of the devices; empty circles and squares represent measured data and solid lines indicate the linear fit of the data. (C) Scanning electron microscopic (SEM) images of MAPbI3 film with 50 mol % urea. (D–H) Elemental distribution mapping images of the film. Dashed rectangular boxes in the images indicate the secondary phase formed at grain boundaries. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 7 Effect of Addition of Urea on Local Electrical Properties (A and B) Conducting AFM images of (A) bare MAPbI3 and (B) MAPbI3 film with 4 mol % urea formed on SnO2-coated ITO substrates. Current images were overlaid on grayscale topology images. (C and D) Line-scan profiles of height and current along the black lines in (A) and (B), respectively. (E) Distribution of measured current between the tip and the surface of the perovskite films. Chem 2017 3, 290-302DOI: (10.1016/j.chempr.2017.05.020) Copyright © 2017 Elsevier Inc. Terms and Conditions