Polar Species for Effective Dielectric Regulation to Achieve High‐Performance CsPbI₃ Solar Cells

Abstract

pathway of the emerging perovskite solar cells (PSCs). [1][2][3][4] The defects in the bulk and at the surface of the perovskite lightharvesting material play vital roles in both the photoelectric conversion efficiency (PCE) and long-term stability. [5][6][7][8] These defects not only scatter charge carriers, giving rise to undesirable nonradiative recombination losses, [6,7] but also act as the predominant reactive sites for water and oxygen. Even worse, defects may serve as migration channels for ionic species that lead to device degradation. [7,[9][10][11] Thus, the presence of defects severely threatens the performance and stability of PSCs. Therefore, there have been numerous reports of efforts focused on lowering the defect density and deactivating defects. [4,[12][13][14][15][16][17][18][19][20][21][22] For effective/targeted defect passivation to further promote the performance of perovskite photovoltaic devices, it is imperative to carefully investigate the defect energy levels, defect types, and defect capturing capability. [6,23,24] Yang et al. characterized the defect energy distribution using admittance spectroscopy. [25] From those results combined with theoretical calculation, they attributed the defect with an activation energy of ≈0.16 eV above the valance band to iodine interstitials (I i ) in methylammonium lead Nonradiative losses caused by defects are the main obstacles to further advancing the efficiency and stability of perovskite solar cells (PSCs). There is focused research to boost the device performance by reducing the number of defects and deactivating defects; however, little attention is paid to the defect-capture capacity. Here, upon systematically examining the defect-capture capacity, highly polarized fluorinated species are designed to modulate the dielectric properties of the perovskite material to minimize its defectcapture radius. On the one hand, fluorinated polar species strengthen the defect dielectric-screening effect via enhancing the dielectric constant of the perovskite film, thus reducing the defect-capture radius. On the other, the fluorinated iodized salt replenishes the I-vacancy defects at the surface, hence lowering the defect density. Consequently, the power-conversion efficiency of an all-inorganic CsPbI 3 PSC is increased to as high as 20.5% with an opencircuit voltage of 1.2 V and a fill factor of 82.87%, all of which are among the highest in their respective categories. Furthermore, the fluorinated species modification also produces a hydrophobic umbrella yielding significantly improved humidity tolerance, and hence long-term stability. The present strategy provides a general approach to effectually regulate the defect-capture radius, thus enhancing the optoelectronic performance.

Tailoring the Interfacial Termination via Dipole Interlayer for High‐Efficiency Perovskite Solar Cells

“…As we all know, fluorescence intensity reflects the radiative recombination between hole and electron. [50][51] Therefore, higher fluorescence intensity reveals that the defect-assisted nonradiative recombination accounts for a lower proportion, indicating the high-quality perovskite film with fewer defects. [52] Meanwhile, the charge carrier lifetimes of the perovskite films were obtained to further solidify the results by fitting the TR-PL spectra with the bi-exponential function.…”

High-Efficiency CsPbI2Br Perovskite Solar Cells with over 83% Fill Factor by Synergistic Effects of a Multifunctional Additive

“…With tremendous research effort on all-inorganic CsPbX 3 -based photovoltaic devices in recent years, CsPbI 3 -based PSCs have achieved efficiencies more than 20% due to their suitable band gap (1.73 eV) and high charge carrier mobility. − Especially, Meng and co-workers recently obtained CsPbI 3 PSCs with the highest efficiency value of 21% by post-treating CsPbI 3 films with phenyltrimethylammonium iodide (PTAI) . However, the photo-active perovskite phase CsPbI 3 (α-phase) structure at room temperature is metastable and can easily and rapidly transform into a photo-inert non-perovskite phase (δ-phase) when exposed to humidity, leading to a dramatic deterioration of the device performance .…”

Orientation Engineering via 2D Seeding for Stable 24.83% Efficiency Perovskite Solar Cells

“…The VBM of the DSM perovskite film shows an obvious upward shift towards the vacuum energy level, which is ascribed to a reduction in charge traps of the perovskite film. [ 15,48 ] The elevated VBM of the DSM perovskite film is well aligned with the highest occupied molecular orbital (HOMO) of the Spiro‐OMeTAD (−5.20 eV), which is beneficial to reducing energy loss for hole transfer. [ 49 ]…”