Hole Conductor Free Perovskite-based Solar Cells-Lioz Etgar-The Hebrew University of Jerusalem.pdf

123 SPRINGER BRIEFS IN APPLIED SCIENCES AND TECHNOLOGY Liozuni00A0Etgar Hole Conductor Free Perovskite- based Solar Cells SpringerBriefs in Applied Sciences and Technology More information about this series at http://www.springer.com/series/8884 Lioz Etgar Hole Conductor Free Perovskite-based Solar Cells 123 Lioz Etgar Institute of Chemistry, Casali Center for Applied Chemistry, the Harvey M. Kruger Family Center for Nanoscience and Nanotechnology The Hebrew University of Jerusalem Jerusalem Israel ISSN 2191-530X ISSN 2191-5318 (electronic) SpringerBriefs in Applied Sciences and Technology ISBN 978-3-319-32989-5 ISBN 978-3-319-32991-8 (eBook) DOI 10.1007/978-3-319-32991-8 Library of Congress Control Number: 2016939937 © The Author(s) 2016 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, speciuniFB01cally the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microuniFB01lms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a speciuniFB01c statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper This Springer imprint is published by Springer Nature The registered company is Springer International Publishing AG Switzerland Preface This brief book results from the extensive work that has been done in my laboratory in the last 3 years. As will be discussed in this brief book, a breakthrough occurs in the photovoltaic (PV) uniFB01eld in the last 4 years. A new material called organo-metal halide perovskite (OMHP) entered the PV uniFB01eld. To be completely correct, the OMHP is not a new material and already in 1990s researchers around the world (mainly from Japan) worked on characterizing this material. But the main progress related to the PV uniFB01eld was made at 2012 as described in more detail in this book. This year was my last year as a postdoctoral researcher in Prof. Gratzel laboratory where I was one of the pioneering researchers working with this exciting material, which results in an early publication on the use of the OMHP as light harvester and hole conductor at the same time in the solar cell. Starting 2012 as established my current research group which have developed further the OMHP as a material and in a PV cell. Even though just 3–4 years past from the main breakthrough with this material, I think it is the right time to summarize the basic fundamental properties and some of its exciting abilities as a fascinating material for optoelectronic applications. This book mainly discusses our discovery that the OMHP can function as hole conductor (HTM) and light harvester in the solar cell at the same time as so-called HTM-free perovskite solar cells. It brings the ability to tune the OMHP properties (e.g., optical, physical, and electronic) and the use of the OMHP in different solar cells structures as we demonstrating the advantageous of this material on the solar cell properties. I would like to express my appreciation to all of my students at the Hebrew University of Jerusalem who worked intensively with passion on this topic; without them, we could not make such an influenced contribution to the uniFB01eld. I also thank Mayra Castro from springer publisher for excellent collaboration. Finally, I would like to thank my wife and my three children for their support, happiness, and love during these years. v Contents 1 Organo-Metal Lead Halide Perovskite Properties 1 1.1 Perovskite Crystal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Perovskite Energy Level. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Absorption CoefuniFB01cient of Perovskite . . . . . . . . . . . . . . . . . . . . . 3 1.4 Balance Charge Transport of Perovskite . . . . . . . . . . . . . . . . . . . 3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2 The Evolution of Perovskite Solar Cells Structures . 5 2.1 Perovskite Solar Cells with Liquid Electrolyte. . . . . . . . . . . . . . . 5 2.2 Perovskite Solar Cells with Solid-State Hole Conductor . . . . . . . . 5 2.3 Perovskite Solar Cells in Planar ConuniFB01guration . . . . . . . . . . . . . . 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 Hole Transport Material (HTM) Free Perovskite Solar Cell 9 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.2 Mesoporous HTM-Free Perovskite Solar Cell . . . . . . . . . . . . . . . 10 3.3 Planar HTM-Free Perovskite Solar Cell [14]. . . . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4 Parameters InuniFB02uencing the Deposition of Methylammonium Lead Halide Iodide in Hole Conductor Free Perovskite-Based Solar Cells. 25 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.2 Spin Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.3 Dipping Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 4.4 Annealing Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 4.5 Methylammonium Iodide Concentration . . . . . . . . . . . . . . . . . . . 30 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 vii 5 Tuning the Optical Properties of Perovskite in HTM Free Solar Cells. 33 5.1 Halide (X-Site) ModiuniFB01cations [1]. . . . . . . . . . . . . . . . . . . . . . . . 33 5.2 Cation (A-Site) ModiuniFB01cations [7] . . . . . . . . . . . . . . . . . . . . . . . 37 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 6 High Voltage in Hole Conductor Free Organo Metal Halide Perovskite Solar Cells 45 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 7 Self-assembly of Perovskite for Fabrication of Semi-transparent Perovskite Solar Cells 51 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 8 Summary . 57 viii Contents Chapter 1 Organo-Metal Lead Halide Perovskite Properties 1.1 Perovskite Crystal Structure The inorganic perovskite compounds were discovered in 1839 and named after the Russian mineralogist L.A. Perovski, who uniFB01rst characterized the structure of per- ovskite compounds with general crystalline formula of ABX 3 . Figure 1.1 shows the basic structural arrangement, where X is anion (oxygen or halogen), A is a bulky cation which occupies a cubo-octahedral site shared with 12X anions, and B is a smaller cation stabilized in an octahedral site shared with 6X anions. Large numbers of inorganic perovskite oxides have been extensively studied due to their electrical properties of ferroelectricity or superconductivity. Halide perovskite received their attention when Mitzi et al. [1] discovered that layered organo-metal halide per- ovskites exhibit semiconductor-to-metal transition with increasing dimensionality. Moreover, the band gap energy decreased with increasing dimensionality, which is suitable for photovoltaic applications. The organo-lead halide perovskite is obtained when in a classical perovskite compound, the A site is replaced by an organic cation, which is often methyl ammonium (CH 3 NH 3 + ) or formamidinium (NH 2 –CH 2 =NH 2 + ). B is usually Pb 2+ , and X is either I − ,Cl − ,orBr − anions. The large organic cation groups balance the charge between the octahedron layers in the 3D network (Fig. 1.1). The formability of the 3D perovskite structure can be estimated by Goldschmidt tolerance factor (t) and an octahedral factor (l)[2]. The tolerance factor is the ratio of the (A–X) distance to the (B–X) distance. And is given by ¼ ðR A þR B Þ ffiffi 2 p ðR B þR X Þ . The octahedral factor is deuniFB01ned as l ¼ R B =R X where R A , R B , and R X are the ionic radii of the corresponding ions at the A, B, X sites, respectively. Formability study of alkali metal halide perovskite determined that ideal cubic structure was stabilized when 0.813 t 1.107 and 0.442 l 0.895 [2]. A smaller t value could lead to a lower symmetry tetragonal or orthorhombic structure, whereas larger t value can destabilize the 3D network, creating a 2D structure [3]. Taking MAPbI 3 , the radii of MA + = 180 pm, Pb 2+ = 119 pm, I − = 220 pm, thus the t factor was calculated to © The Author(s) 2016 L. Etgar, Hole Conductor Free Perovskite-based Solar Cells, SpringerBriefs in Applied Sciences and Technology, DOI 10.1007/978-3-319-32991-8_1 1 be 0.83 and l factor is 0.54 [4] as a result, MAPbI 3 is expected to have a cubic structure. However, phase transition in MAPbX 3 also occurs when temperature is varying. At temperature below 162 K MAPbI 3 forms in an orthorhombic phase, by increasing the temperature up to 327 K it transforms to tetragonal phase, and as temperature increase above 327 K, MAPbI 3 undergoes transition phase to the cubic phase [4]. Therefore, at room temperature MAPbI 3 holds tetragonal structure. 1.2 Perovskite Energy Level Organo -metal halide perovskite compounds have wide-direct band gaps, which can be tuned by either changing the alkyl group, the metal atom or the halide [5, 6]. Kim et al. studied the direct band gap of tetragonal MAPbI 3 , the optical band gap (E g ) was determined using diffuse reflectance spectroscopy, and the valance band maximum(E VB )wasdeterminedusingUltraviolet photoelectronspectroscopy(UPS). The optical band gap of MAPbI 3 deposited on mesoporous TiO 2 was found to be 1.5 eV, and the valance band energy position was estimated to be −5.43 eV below vacuum level using UPS [7], which is consistent with the previous report [8]. From the optical band gap and the position of the valence band, the conduction band (E CB ) was estimated to be −3.93 eV, as the energy band gap of MAPbBr 3 reported to be 2.2 eV [9], and for MAPbCl 3 3.11 eV [10]. Moreover, phase transformation due to change in temperature also affect the bang gap. Lower symmetry of orthorhombic increases the optical gap to 1.6 eV, and higher symmetry of the cubic phase decreases the optical band gap to 1.3 eV [4]. Reducing the optical band gap A B X (a) (b) Fig. 1.1 a Ball and stick model of the basic cubic perovskite structure and b their extended network structure connected by the corner-shared octahedral 2 1 Organo-Metal Lead Halide Perovskite Properties is possible by replacing the organic group with a larger group, such as NH 2 –CH 2 =NH + 2 , or by replacing the lead with tin (Sn) [11–13]. 1.3 Absorption CoefuniFB01cient of Perovskite Organo-lead halide perovskites have drawn substantial interest as a light harvester due to their absorption onset of more than 800 nm in the visible spectrum, and due to their large absorption coefuniFB01cient [3, 14–16] that is crucial for PV application. Perovskite showed an absorption coefuniFB01cient that is 10 times greater than that of the N719 conventional dye molecule used so far in DSSC. The absorption coefuniFB01cient of MAPbI 3 at 550 nm wavelength is 1.5 C2 10 4 cm −1 , indicating penetration depth of 0.66 lm[14]. The absorption coefuniFB01cients of perovskite versus silicon and GaAs was compared, [3] presenting that perovskite has much higher absorption coefuniFB01- cient than silicon and GaAs due to its direct band gap and its higher density of state. 1.4 Balance Charge Transport of Perovskite In addition for having high absorption coefuniFB01cient, Perovskite is also characterized by efuniFB01cient electron and hole transport properties. Due to its balance charge transport property, fabrication of solar cell without hole transport material and mesoporous TiO 2 with high efuniFB01ciencies is possible, which is impossible in con- ventional dye sensitized solar cells. The electron diffusion length for MAPbI 3 was estimated as 130 nm, and the hole diffusion length was estimated as 100 nm, For MAPbI 3−x Cl x the electron diffusion length of electron was about 1069 nm, while the hole diffusion length was about 1213 nm [16, 17]. The recombination time of the electron and hole is very slow, in tens of microseconds. Moreover, charge accumulation properties were identiuniFB01ed for perovskite. The result indicated the existence of high-density state and supported the weakly bounded excitons in perovskite, which can lead to a high open-circuit voltage in perovskite solar cells [18]. References 1. Mitzi DB, Feild CA, Harrison WTA, Guloy AM (1994) Conducting tin halides with a layered organic-based perovskite structure. Nature 369:467–469 2. Li C, Lu X, Ding W, Feng L, Gao Y, Guo Z (2008) Formability of ABX3 (X = F, Cl, Br, I) halide perovskites. Acta Crystallogr B 64:702–707 3. Yin WJ, Yang JH, Kang J, Yan Y, Wei S-H (2015) Halide perovskite materials for solar cells: a theoretical review. J Mater Chem A 3:8926–8942 1.2 Perovskite Energy Level 3 4. Liu X, Zhao W, Cui H, Xie Y, Wang Y, Xu T, Huang F (2015) Organic–inorganic halide perovskite based solar cells—revolutionary progress in photovoltaics. Inorg Chem Front 2:315–335 5. Mitzi DB (2000) Templating and structural engineering in organic–inorganic perovskites. J Chem Soc, Dalton Trans 1:1–12 6. Knutson JL, Martin JD, Mitzi DB (2005) Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating. Inorg Chem 44:4699–4705 7. Kim H-S, Lee C-R, Im J-H, Lee K-B, Moehl T, Marchioro A, Moon S-J, Baker R-H, Yum J-H, Moser JE, Grätzel M, Park N-G (2012) Lead iodide perovskite sensitized all-solid-state submicron thin uniFB01lm mesoscopic solar cell with efuniFB01ciency exceeding 9 %. Sci Rep 2:591 8. Schulz P, Edri E, Kirmayer S, Hodes G, Cahen D, Kahn A (2014) Interface energetics in organo-metal halide perovskite-based photovoltaic cells. Energy Environ Sci 7:1377–1381 9. Noh JH, Im SH, Heo JH, Mandal TN, Seok SI (2013) Chemical management for colorful, efuniFB01cient, and stable inorganic–organic hybrid nanostructured solar cells. Nano Lett 13:1764– 1769 10. Kitazawa N, Watanabe Y, Nakamura Y (2002) Optical properties of CH3NH3PbX3 (X = halogen) and their mixed-halide crystals. J Mater Sci 37:3585–3587 1