Synergistic Effect of Ammonium Salts in Sequential Deposition toward Efficient Wide-Band-Gap Perovskite Photovoltaics with PCE Exceeding 20%

Abstract

The controlled crystallization process is of significance to the morphological quality of wide-band-gap perovskite absorbers, especially with excessive bromide ions. Moreover, the non-radiative recombination assisted by surface defects is one of the major unfavorable factors that confines the development of highly efficient wide-band-gap perovskite solar cells (PSCs). Here, 1.65 eV wide-band-gap PSCs are constructed by a sequential deposition method with tailored morphology of highly reproducible perovskite absorbers. The controlled crystallization with the help of NH 4 Cl enables the perovskite films with larger and more uniform grains, which result in less bulk defects. At the same time, (NH 4 ) 2 SO 4 as a passivation layer reduces the uncoordinated Pb 2+ and Pb 0 defects on the surface of the perovskite film and improves the hydrophobicity due to newly formed insoluble PbSO 4 . Eventually, the synergistic effect of ammonium salts results in a high V OC of 1.18 V and an optimal efficiency of 20.43%, which is one of the highest power conversion efficiencies for 1.65 eV wide-band-gap-based PSCs constructed by a two-step deposition process. This work confirms that the sequential deposition method and addition of proper ammonium salts are effective strategies toward highly efficient and stable wide-band-gap PSCs.

Intermediate Phase Engineering for Efficient and Stable All-Inorganic Perovskite Solar Cells

“…X-ray photoelectron spectroscopy (XPS) analysis was performed to investigate the elemental composition and interactions within the PVK layer after the addition of NH 4 Cl. The introduction of Cl – into CsPbBr 3 films leads to passivation of Pb and Cs dangling bonds, resulting in a shift of Pb 4f and Cs 3d toward higher binding energy (Figure d,e). , Additionally, the NH 4 + cations passivate negatively charged defects through ionic bonding with uncoordinated Br – , causing a shift in the Br 3d binding energy toward higher values (Figure f). , The energy-dispersive X-ray spectroscopy (EDS) mapping image demonstrates the homogeneous distribution of Cl from NH 4 Cl in PbBr 2 and CsPbBr 3 films (Figure S10), thereby correlating the findings from XPS analysis. Based on the aforementioned investigations, a mechanistic understanding of NH 4 Cl passivation in PVK can be presented, as depicted in Figure g.…”

“…The introduction of Cl − into CsPbBr 3 films leads to passivation of Pb and Cs dangling bonds, resulting in a shift of Pb 4f and Cs 3d toward higher binding energy (Figure 2d,e). 33,34 Additionally, the NH 4 + cations passivate negatively charged defects through ionic bonding with uncoordinated Br − , causing a shift in the Br 3d binding energy toward higher values (Figure 2f). 32,34 The energy-dispersive X-ray spectroscopy (EDS) mapping image demonstrates the homogeneous distribution of Cl from NH 4 Cl in PbBr 2 and CsPbBr 3 films (Figure S10), thereby correlating the findings from XPS analysis.…”