Black‐Yellow Bandgap Trade‐Off During Thermal Stability Tests in Low‐Temperature Eu‐Doped CsPbI₃

Abstract

The black γ‐phase of CsPbI3 with its bandgap at ≈1.75 eV can enable the take‐off of tandem solar cells as soon as intrinsic instability to the yellow δ‐phase is solved. Here, a black γ‐phase is formed at low temperature (80–90 °C) by incorporating Eu through EuCl3 or EuI2. It is forced to become yellow by thermal heating under nitrogen. It is demonstrated how spectroscopic ellipsometry and the related critical points analysis provide a new diagnostic tool to monitor the transformation through the bandgap footprint. As two sides of the same coin, the consumption of the black γ‐phase and the growth of the yellow δ‐phase are addressed and modeled in the range of 60–100 °C using the Avrami's theory. This approach allows extracting the activation energies of the phase transformation that are 0.95 eV versus 1.15 eV using EuI2 and EuCl3, respectively. In situ transmission electron microscopy analyses combined with fast marching simulations highlight that the phase transformation occurs through constant nucleation and growth. Europium has indeed the capability to tackle those processes and to extend the durability of the black γ‐phase at 30 °C in N2 to ≈250 days, hugely above the one observed without Eu (≈hours).

Out‐of‐Glovebox Integration of Recyclable Europium‐Doped CsPbI3 in Triple‐Mesoscopic Carbon‐Based Solar Cells Exceeding 9% Efficiency

“…The samples with Eu show a smaller c-value (the longest axis) with respect to pure CsPbI 3 , producing a slightly measurable contraction of the unit cell volume, [41] similarly as reported in our recent work [35] for black LT γ-phase formed at 80 °C. As a difference between the CsPbI 3 LT γ-phase and HT γ-phase, the crystallite size was found to have an average diameter of 20 nm and 52 nm in the two cases, respectively.…”

First Experimental Evidence of Amorphous Tin Oxide Formation in Lead‐Free Perovskites by Spectroscopic Ellipsometry

“…Figure a–c shows data corresponding to the most important CPs present in the as‐prepared material E g (≈1.45 eV), E 1 (≈1.8 eV) and E 3 (≈3.7 eV) and one extra CP ( E ox ) required to fit the experimental data when the SnO 2 signal appears, that is located at ≈3.5 eV. In addition to the energy, as previously demonstrated, [ 36,37 ] the amplitude (see. Equation () and ()) is an important parameter strictly related to the amount of material in a specific phase inside the layer.…”

“…FASnI 3 precursor solution with additives dipropylammonium iodide (DipI) and NaBH 4 :298 mg of SnI 2 (0.8 M), 123.81 mg of FAI (0.72 M), 36.65 mg of DipI (0.16 M), 12.48 mg of SnF 2 (0.08 M) and 0.1 mg of NaBH 4 (0.0026 M, may vary depending on the precursor purity, brand or Batch) were dissolved in 1 mL of a binary mixture of DMSO:DMF (9:1, v/v) and stirred overnight at room temperature.…”

Advancing Efficiency and Stability of Lead, Tin, and Lead/Tin Perovskite Solar Cells: Strategies and Perspectives

“…[94,95] Moving away from organic cations entirely, all inorganic CsPbI 3 offers superior material stability and is considered as priority in the APbI 3 family for improved device stability. [87,96,97] Yet, its bandgap is larger Relations between perovskite composition and bandgap. UV-vis absorption spectra; effect of a) A-and B-sites in ABI 3 .…”

“…[ 94,95 ] Moving away from organic cations entirely, all inorganic CsPbI 3 offers superior material stability and is considered as priority in the APbI 3 family for improved device stability. [ 87,96,97 ] Yet, its bandgap is larger than the optimal bandgap for single‐junction solar cells and is mainly considered for tandem applications. [ 98,99 ]…”