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

Abstract

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−x Cs x Pb(I 1−y Br 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 singlejunction p-i-n devices with a V OC of 1.22 V and a champion maximumpower-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.

Dual Interface Passivation in Mixed-Halide Perovskite Solar Cells by Bilateral Amine

“…The target thin films showed a slight reduction in absorption intensity compared to the control thin films. However, the absorption offset observed no obvious change, which is different from previously reported passivation schemes using primary amines and secondary amines. ,, …”

“…However, the absorption offset observed no obvious change, which is different from previously reported passivation schemes using primary amines and secondary amines. 39,42,43 There is no significant effect of the passivation on the band gap of the target thin films, but the absorption coefficient of the target thin films reduced slightly at the longer wavelengths. However, both thin films have a similar band gap of ∼1.63 eV as calculated from the Tauc plot (Figure S2).…”

Prospects for Tin-Containing Halide Perovskite Photovoltaics

“…Alternatively, for other amines, amine-FA + condensation reactions expelling ammonia can take place, as first identified for methylamine (MA) in solution . This could happen at the surface, such as when modified with 3-(aminomethyl)­pyridine (3-APy), and most likely ethylenediamine (EDA) and all other linear alkylamines. , In the case of 3-APy having the product MPyFA + ( N -(3-methylpyridine) formamidinium), or for amine-MA + , a simple transfer or sharing of acidic protons happens, forming 3APy + . The authors of this study propose the MPyFA + cation sites at the A-site of the perovskite, with the pyridine ring promoting the formation of positively charged V I (iodide vacancies), which act as shallow donors and induce a field that facilitates electron extraction.…”

Elucidating the Role of Contact-Induced Gap States and Passivation Molecules at Perovskite/Metal Contacts

“…Experimentally, PbI 2 -termination provides the best photovoltaic performance . Following refs and , we study a nonstoichiometric MAPbI 3 slab with symmetric terminations to avoid an artificial dipole. The structural relaxation is continued until the total energy is converged to 10 –5 eV and the atomic forces are converged to 0.01 eV/Å.…”