Paper

Ethylenediamine Addition Improves Performance and Suppresses Phase Instabilities in Mixed-Halide Perovskites

Wang, Jian, Barlow, Stephen, Ginger, David S, McCarthy, Declan P, Smith, Joel A, Drysdale, James N, Shi, Yangwei, Westbrook, Robert J E, Zhou, Suer, Snaith, Henry J, Gallant, Benjamin M, Taddei, Margherita, Marder, Seth R

2022

Overview

We show that adding ethylenediamine (EDA) to perovskite precursor solution improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA1-xCsxPb(I1-yBry)3 which are currently of interest for perovskite-on-Si tandem solar cells. Using spectroscopy and hyperspectral microscopy, we show that the additive improves film homogeneity and suppresses the phase instability that is ubiquitous in high-Br perovskite formulations, producing films that remain stable for over 100 days in ambient conditions. With the addition of 1 mol% EDA we demonstrate 1.69 eV-gap perovskite single-junction p-i-n devices with a VOC of 1.22 V, and a champion maximum power point tracked power conversion efficiency of 18.8%, comparable to the best reported methylammonium-free perovskites. Using nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction techniques, we show that EDA reacts with FA+ in solution, rapidly and quantitatively forming imidazolinium cations. It is the presence of imidazolinium during crystallization which drives the improved perovskite thin-film properties.

• Publisher: Cornell University Library, arXiv.org
• Subject: Cesium / Crystallization / Energy conversion efficiency / Ethylenediamine / Homogeneity / Lead compounds / Maximum power / Metal halides / NMR / NMR spectroscopy / Nuclear magnetic resonance / Performance enhancement / Perovskites / Photovoltaic cells / Solar cells / Spectrum analysis / Thin films