Ethylenediamine addition improves performance and suppresses phase instabilities in mixed-halide perovskites

Journal article

We show that adding ethylenediamine (EDA) to perovskite precursor solutions improves the photovoltaic device performance and material stability of high-bromide-content, methylammonium-free, formamidinium cesium lead halide perovskites FA_1–xCs_xPb(I_1–yBr_y)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 V_OC 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.

Authors: Taddei, M; Smith, JA; Gallant, BM; Zhou, S; Westbrook, RJE

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: ACS Energy Letters
• Volume: 7
• Issue: 12
• Pages: 4265-4273
• Publication date: 2022-11-02
• Acceptance date: 2022-10-20
• DOI: 10.1021/acsenergylett.2c01998
• EISSN: 2380-8195
• ISSN: 2380-8195
• Language: English
• Keywords: FFR