Black Phase of Inorganic Perovskite Stabilized with Carboxyimidazolium Iodide for Stable and Efficient Inverted Perovskite Solar Cells

Abstract

As all-inorganic perovskite (CsPbI3–x Br x ) is prone to phase transition from the α phase (black phase) to the δ phase (yellow phase) in a humid environment or under heating, improving the phase stability of all-inorganic perovskite of the black phase is one of the urgent problems to solve. Herein, 1,2-dimethyl-3-acetylimidazolium iodide (DMAII) is spin-coated onto the surface of CsPbI3–x Br x perovskite for use in p–i–n perovskite solar cells (PSCs). We find that the DMAII coating has two effects on the CsPbI3–x Br x perovskite film: surface passivation and phase stabilization of perovskite. Traps in the CsPbI3–x Br x perovskite film can be reduced significantly by DMAII passivation, resulting in enhanced hole extraction and suppressed charge recombination. Consequently, the power conversion efficiency (PCE) is improved from 10.81 to 13.14%. Moreover, the DMAII coating can significantly inhibit the phase transition from the α phase to the δ phase in a humid environment or under heating, as characterized by the X-ray diffraction pattern, UV–vis absorption spectrum, and film color. After exposing the CsPbI3–x Br x perovskite films to a humid atmosphere (relative humidity = 40–60%) for 6 h, the PCE decreases dramatically to only 0.12% of the initial PCE for the PSC without the DMAII coating, while the PCE maintains 80% of the initial PCE for the PSC with the DMAII coating. In addition, when the PSC devices are heated at 120 °C for 4 h, the control PSC shows a 96% decrease in PCE, while the PCE decay is only 9% for the DMAII-coated PSC. These findings indicate that carboxyl-substituted imidazolium iodide is a kind of promising material to not only passivate traps but also stabilize the black phase of all-inorganic perovskite.

The synergistic effect of defect passivation and energy level adjustment for low-temperature carbon-based CsPbI2Br perovskite solar cells

“…This spectral change could be ascribed to the coordination interactions between C–N and Pb 2+ . 46,48 In addition, the stretching vibration peak of the C–F bond located at about 1230 cm −1 shifted to lower wavenumber in the fluorinated organic ammonium halide salts/lead halides complex samples, indicating the reinforced interaction, which is also expected to passivate Pb 2+ defects. 39,49 Based on the above results, we concluded that the amino group and C–F bond could connect molecules to the Pb–X framework by coordinating with the under-coordinated Pb 2+ or hydrogen bonding with the halogen ions and finally passivated CsPbI 2 Br defects.…”

Tiny spots to light the future: advances in synthesis, properties, and application of perovskite nanocrystals in solar cells

“…254,259 The stabilization of the desired bulk α-CsPbI 3 phase is only achieved at high temperatures (>150 °C), [260][261][262] and this material is prone to oxygen and moisture degradation, which can be attributed to its low tolerance fact or (0.803). 263 For that reason, it is quite hard to obtain long-term stability in bulk CsPbI 3 -based solar cells, and the exposure of the unencapsulated device to ambient air results in the irreversible formation of the yellow non-photoactive phase. 264,265 On the other hand, PSCs prepared using CsPbI 3 NCs (E g ∼ 1.72 eV, excellent for top-cell in tandem solar cells), are not only more stable under ambient conditions compared to the bulk analog, but also allow stabilization of the photoactive phase at room temperature.…”

Recent Progress on Defect Passivation of All‐Inorganic Halide Perovskite Solar Cells

“…DMAII provides electrons to the Pb 2+ ions to form coordination bonds, and the binding energy of electrons was thus reduced, which served to passivate the surface defects and achieved the best PCE of 13.14% for the inverted PSCs structure. [94] Du et al prepared CsPbI 3 thin films containing low concentration of a novel ionic liquid EMIMHSO 4 , which successfully reduced the perovskite grain boundaries, strongly coordinated with the under-coordinated Pb 2+ to passivate iodide vacancy defects. The results showed that the PCE of CsPbI 3 solar cells was as high as 20.01%.…”