Article pubs.acs.org/JPCC
Polymer-Assisted Construction of Mesoporous TiO2 Layers for Improving Perovskite Solar Cell Performance Youfeng Yue,† Tomokazu Umeyama,‡ Yuki Kohara,‡ Hitoshi Kashio,‡ Masateru Itoh,† Seigo Ito,§ Easan Sivaniah,*,† and Hiroshi Imahori*,‡,∥ †
Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan § Department of Materials and Synchrotron Radiation Engineering, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan ∥ Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan ‡
S Supporting Information *
ABSTRACT: A general polymer, poly(methyl methacrylate) (PMMA) is utilized as a unique templating agent for forming crack-free mesoporous TiO2 films by a sol−gel method. The pore morphologies were found to be controllable by varying the amount of PMMA. The PMMA-mediated mesoporous TiO2 layer has been applied for the first time to perovskite solar cells exhibiting a best power conversion efficiency of ≥14%, which is ca. three times higher than that using a TiO2 layer prepared by the same sol−gel method without the polymer addition (5.28%). Remarkably, it was superior to the reference device with mesoporous TiO2 layer prepared with conventional nanoparticle paste (13.1%). Such mesostructure-tuned TiO2 layers made by the facile sol−gel technique with a commercially available polymer additive has the great potential to contribute significantly toward the development of low-cost, highly efficient perovskite solar cells as well as other functional hybrid devices.
■
INTRODUCTION
perovskites (CH3NH3PbX3, X = halogen). Recently, all-solid perovskite solar cells have offered the promise of a breakthrough for next-generation photovoltaic devices,10−22 reaching power conversion efficiency (PCE) values of 14− 20%.14−16,20−22 A typical cell architecture consists of a perovskite light-harvesting layer sandwiched between holetransporting material (HTM) and electron-transporting compact TiO2 (cTiO2) layers. Mesoporous TiO2 (mTiO2) scaffold is frequently integrated as the promising electron conduction pathway to collect the carrier effectively at the electrode.11−14,19,20,22 The mTiO2 in perovskite solar cells is generally prepared by spin-coating a paste containing TiO2 nanoparticles to form a TiO2 film with high surface area.23 However, the preparation of the TiO2 nanoparticle pastes is time-consuming and tedious, thereby inhibiting the advantages of cost-effective perovskite solar cells. Furthermore, perovskite crystallization in the mesoporous TiO2 scaffolds often suffers from incomplete crystalline formation, depending on size of the employed TiO2 nanoparticles.24−26 Herein, we show the utilization of a general polymer, poly(methyl methacrylate) (PMMA) as a unique templating agent for forming crack-free mesoporous TiO2 films by a sol− gel method.9,27 We examined the effects of polymer additions
Ordered mesoporous TiO2 (mTiO2 ) materials with a crystalline framework and tailored pore structure have attracted enormous attention in recent years due to their promising applications in photocatalysis, lithium batteries, gas sensing, and photovoltaic devices.1−4 Various synthetic strategies based on sol−gel reactions using structure-directing soft templates, such as surfactants, primary alkylamines, and block copolymers have been developed to prepare crystalline TiO2 with well-defined mesopores. Among them, evaporation induced self-assembly (EISA) approaches with block copolymer templates in organic media are predominantly employed because the hydrolysis and condensation of highly reactive titanium precursors, i.e., titanium alkoxides and chlorides, can be well regulated and restrained during the sol−gel reaction as a result of the absence of water.1−6 Poly(alkylene oxide)-based block copolymers, e.g., poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic P123), are often used to define the structural entity at a nanometer scale. However, the mTiO2 films prepared by the EISA methods typically possess limited pore sizes of
