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High Performance Planar Heterojunction Perovskite Solar Cells with Fullerene Derivatives as the Electron Transport Layer Chang Liu, Kai Wang, Pengcheng Du, Tianyu Meng, Xinfei Yu, Stephen Cheng, and Xiong Gong ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/am506869k • Publication Date (Web): 16 Dec 2014 Downloaded from http://pubs.acs.org on December 22, 2014
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ACS Applied Materials & Interfaces
High Performance Planar Heterojunction Perovskite Solar Cells with Fullerene Derivatives as the Electron Transport Layer Chang Liu, Kai Wang, Pengcheng Du, Tianyu Meng, Xinfei Yu, Stephen Z. D. Cheng and Xiong Gong* College of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325, USA
Abstract In this study, we report the utilization of solution-processed high electrical conductive [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) combined with solution-processed TiO2 as the electron transport layer (ETL) to overcome extremely low electrical conductivity of solutionprocessed TiO2 ETL in planar heterojunction (PHJ) perovskite hybrid solar cells (pero-HSCs). Due to the much more preferable electron extraction and transportation of PC61BM at the cathode side, tremendously boosted short-circuit current density (JSC), fill factor (FF) with enhanced power conversion efficiency (PCE) are observed. In order to further address the wettability issues of perovskite materials on the top of PC61BM, water soluble fullerene derivative is applied to modulate the surface of PC61BM. Consequently, further advanced FF with slightly enlarged JSC and open-circuit voltage (VOC) are observed. The resulted PCE is comparable with the meso-superstructured solar cells in which high PCEs can be produced. Our studies certainly provide a simple approach to boost the efficiency of PHJ pero-HSCs.
Key words: high performance; perovskite solar cells; fullerene derivatives; electron transport layer; electrical conductivity; high short circuit current. *Corresponding author, E-mail:
[email protected]; Fax: (330) 972-3406
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1. Introduction In recent years, the organometal halide perovskite, CH3NH3PbX3, where X is a halogen atom (I, Cl, Br, or a combination of some of them) with polycrystalline structure, has been intensively developed for photovoltaic application.1 Organometal halide perovskite materials are direct bandgap semiconductors with an approximately ideal bandgap of ~1.55 eV and a high absorption extinction coefficient.2-4 In addition, perovskite materials also possess ambipolar transport properties that enables both hole and electron transporting in perovskite hybrid solar cells (peroHSCs).5,6 CH3NH3PbX3 was first utilized in dye-sensitized solar cells by Miyasaka and coworkers in 2009.1 After that, CH3NH3PbX3 has been applied in a variety of other solar cell architectures.7-10 On account of the long charge carrier diffusion length of perovskite materials (~1µm in CH3NH3PbI3-xClx, ~100 nm in CH3NH3PbI3),11 planar heterojunction (PHJ) pero-HSCs has been progressively developed, with power conversion efficiency (PCE) ranging from 3% to over 15% in the past years.7-9,12-16 Moreover, simple fabrication process makes the PHJ construction appealing to large area manufacturing as comparison with their mesosuperstructured solar cells (MSSCs) counterparts,17,18 where the high temperature sintering process of mesoporous metal oxide and the homogeneous infiltration of perovskite materials into the mesoporous electron transport material are major issues. Consequently, high efficiency PHJ pero-HSCs from low-temperature solution processing would be much more advantageous. However, a severe limitation of the PHJ architecture that restricts the solar cell performance is the extremely low electrical conductivity of compact TiO2 layer (~10-11S/□).19 Charge carriers transport from perovskite materials to the cathode electrode would be drastically suppressed, insinuating the moderate short-circuit current density (JSC) and fill factor (FF). Furthermore, due to the shorter diffusion length of electrons than that of holes in CH3NH3PbI3 perovskite material
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