Transamidation of dimethylformamide during alkylammonium lead triiodide film formation for perovskite solar cells
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Perovskite-based solar cells, typically CH3NH3PbI3, have reached power conversion efficiencies on par with single crystal silicon solar cells. Perovskite cells prepared with the most common perovskite solvent N,N-dimethylformamide (DMF) by different research groups exhibit disparate efficiencies and stability for nominally identical perovskite films. Although the differences can be related to processing conditions, a consistent physical cause for the differences has been lacking. Highly-sensitive time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveals significant dimethylamine (DMA) included in perovskite films. TOF-SIMS and x-ray photoelectron spectroscopy results suggest DMA levels ranging from roughly 10–50%. Only the highest levels register as perovskite peak shifts in x-ray diffraction; lower levels are invisible. We propose that methylamine (MA) can react with DMF solvent by transamidation to produce dimethylamine (DMA), which then displaces some MA in perovskite crystals, see Fig. 1. Transamidation of DMF can be catalyzed by TiO2, Al2O3, water, or acid, but in perovskite films transamidation is inhibited by water.
Yabing Qi
Professor Yabing Qi is Head of Energy Materials and Surface Sciences Unit in Okinawa Institute of Science and Technology Graduate University. Dr. Qi received his BS, MPhil, and Ph.D. degrees from Nanjing University, Hong Kong University of Science and Technology, and University of California Berkeley, respectively. Prior to his current appointment, he was a postdoctoral fellow in Princeton University. His research interests include perovskite solar cells, organic electronics, energy storage, surface sciences, advanced material characterization, energy materials and devices. Dr. Qi has co-authored 501 peer-refereed papers and is the co-inventor of 9 patent applications. As the symposium chair, Dr. Qi organized International Symposium on Organic Electronics (Okinawa, Japan; October 3–5, 2012) and International Symposium on Functional Materials (Okinawa, Japan; January 25–29, 2016). In the 2015 MRS Fall Meeting & Exhibit, Dr. Qi co-organized Symposium AA: Organic Semiconductors— Surface, Interface and Bulk Doping. In the coming 2016 MRS Fall Meeting & Exhibit, Dr. Qi will co-organize Symposium ES3: Perovskite Solar Cell Research from Material Properties to Photovoltaic Function. In the coming 2017 MRS Spring Meeting & Exhibit, as the lead organizer Dr. Qi will organize Symposium ES1: Perovskite Solar Cells—Towards Commercialization.
I. INTRODUCTION
Perovskite-based solar cells (PSCs) are currently the leading contender for low-cost solar power. PSCs have far exceeded the power conversion efficiency (PCE) benchmark for commercialization with certified efficiencies exceeding even 20%.1–6 But significant commercialization barriers remain—most notably improving reproducibility and stability.5,7 Diverse strategies have improved film morphology of methylammonium lead halide (MAPbX3) perovskites, e.g., increasing crystal Contributing Editor: Tao Xie a) Address all correspondence to this author. e-m
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