Effective Passivation of Perovskite Solar Cells Involving a Unique Secondary Ammonium Halide Modulator

Abstract

Aromatic ammonium salts have been regarded as the promising passivators in perovskite solar cell (PSC) fabrications. However, the complicated passivation procedure and inevitable formation of undesirable low‐dimensional (LD) perovskite layers limit further development. Furthermore, how the steric and electronic properties of different ammonium cations would influence the passivation is not well understood. Herein, two carefully engineered passivators based on the unique benzothiophene moiety involving the primary and secondary ammonium terminals, BTMA‐1 and BTMA‐2, respectively, are developed. It is shown that defects and, thus, nonradiative recombination reactions are effectively suppressed by simple posttreatments without the formation of LD perovskite. Interestingly, the champion efficiency of the BTMA‐2‐treated device increases to 23.10% from ≈20%, along with great stabilities and negligible hysteresis. An in‐depth understanding of the passivation effect influenced by steric and electronic properties is explored. The extra electron‐donating methyl on the ammonium nitrogen (BTMA‐2) increases the electron density on the N atom and the N–H+ ionic bond is, thus, boosted, which helps the positive terminal to anchor more tightly to the [PbI6]4− structure of the perovskite resulting in improved passivation effects. This novel and promising design strategy for ammonium passivators can promote PSCs to achieve further breakthroughs in both efficiency and stabilities.

Bifunctional Interface Passivation via Copper Acetylacetonate for Efficient and Stable Perovskite Solar Cells

“…This could result from the fact that copper ions occupy lead vacancies to bond with iodine, or iodide ions are implicated by Pb 2+ in the octahedron of the perovskite. 55 Similarly, the Raman peak at 169 cm −1 (assigned to the typical signature of PbI 2 ) shifted to 163 cm −1 (Figure 3c), which is consistent with the XPS results. Moreover, another typical peak of PbI 2 at 216 cm −1 (which belongs to the second-order band of the 110 cm −1 absorption peak) disappeared.…”

“…In addition, similar low binding energy shifts are observed in the I 3d 5/3 and 3d 3/2 signals (Figure b). This could result from the fact that copper ions occupy lead vacancies to bond with iodine, or iodide ions are implicated by Pb 2+ in the octahedron of the perovskite . Similarly, the Raman peak at 169 cm –1 (assigned to the typical signature of PbI 2 ) shifted to 163 cm –1 (Figure c), which is consistent with the XPS results.…”

Recent advances in ionic molecules applied in perovskite solar cells

“…Cui et al employed two benzothiophene-based ammonium iodides, BTMA-1 and BTMA-2, to treat perovskite films. 41 No LD phases were observed due to the steric hindrance of benzothiophene. Both molecules could passivate the surface defects via hydrogen bonds and electrostatic interaction; however, the extra electron-donating methyl group in BTMA-2 could increase the electron density around the N atom and strengthen the N–H + hydrogen bonds, resulting in a better passivation effect.…”

“…Furthermore, a dual passivation strategy combining treatment before and after Fig. 5 Chemical structures of PAI, 3-APAI, 5-AVAI, 39,43 AUDAI, 40 BTMA-1, BTMA-2, 41 HETACl, BTACl, 42 BDABr, 44 BzMIMI, 45 F-LYS-S, 46 L-cysteine, D-cysteine, 47 Py, Py-NH 2 , Py-COOH, Py-CHO 48 and FID. 49 perovskite deposition was demonstrated with metformin hydrochloride (MFCl), which contains positively charged ammonium groups and negatively charged amine and imine groups.…”

Charged Hole‐Transporting Materials Based on Imidazolium for Defect Passivation in Inverted Perovskite Solar Cells

“…[3][4][5] There are a variety of evolving solar photovoltaic technologies, including traditional inorganic solar cells, [6,7] organic solar cells, [8,9] dye-sensitized solar cells, [10][11][12] and perovskite solar cells (PSCs), [13][14][15][16][17] all of which have the potential to harness solar energy on a large scale. Among these promising next-generation photovoltaic technologies, solution-processed halide PSCs are emerging as one of the most promising photovoltaic technology that delivers excellent power conversion efficiency (PCE) over 25.5%, [18][19][20][21][22][23][24] approaching the singlecrystalline silicon photovoltaics performance. This could significantly reduce the solar panel production over power output (or dollar per watt) cost.…”