Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

Carolin M. Sutter-Fella; Yanbo Li; Nicola Cefarin; Aya Buckley; Quynh Phuong Ngo; Ali Javey; Ian D. Sharp; Francesca M. Toma

doi:10.3791/55404

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Method Article

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

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DOI:

10.3791/55404

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September 8th, 2017

Carolin M. Sutter-Fella^*¹^,²^,³ , Yanbo Li^*¹^,⁴ , Nicola Cefarin¹^,⁵^,⁶ , Aya Buckley¹^,⁷ , Quynh Phuong Ngo⁸^,⁹ , Ali Javey²^,³ , Ian D. Sharp¹ , Francesca M. Toma¹

¹Joint Center for Artificial Photosynthesis, Chemical Sciences Division, Lawrence Berkeley National Laboratory, ²Electrical Engineering and Computer Sciences, University of California, Berkeley, ³Materials Science Division, Lawrence Berkeley National Laboratory, ⁴Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, ⁵Department of Physics, Graduate School of Nanotechnology, University of Trieste, ⁶TASC Laboratory, IOM-CNR - Istituto Officina dei Materiali, ⁷Department of Chemistry, University of California, Berkeley, ⁸Materials Science and Engineering, University of California, Berkeley, ⁹Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory

^* These authors contributed equally

Summary

Here, we present a protocol for the synthesis of CH₃NH₃I and CH₃NH₃Br precursors and the subsequent formation of pinhole-free, continuous CH₃NH₃PbI_3-xBr_x thin films for the application in high efficiency solar cells and other optoelectronic devices.

Abstract

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH₃NH₃I) and methylammonium bromide (CH₃NH₃Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH₃NH₃PbX₃ with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH₃NH₃PbI_3-xBr_x by exposing the substrate to vapors of a mixture of CH₃NH₃I and CH₃NH₃Br at reduced pressure and 120 °C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH₃NH₃PbI_3-xBr_x with 0 ≤ x ≤ 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV ≤ E_g≤ 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH₃NH₃PbI_3-xCl_x. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Introduction

Hybrid organic-inorganic lead halide perovskites (CH₃NH₃PbX₃, X = I, Br, Cl) are a new class of semiconductors that has emerged rapidly within the last few years. This material class shows excellent semiconductor properties, such as high absorption coefficient¹, tunable bandgap², long charge carrier diffusion length³, high defect tolerance⁴, and high photoluminescence quantum yield⁵^,⁶. The unique combination of these characteristics makes lead halide perovskites very attractive for a....