Unveiling the Importance of Precursor Preparation for Highly Efficient and Stable Phenethylammonium‐Based Perovskite Solar Cells

Abstract

For the fabrication of low‐dimensional perovskite solar cells, understanding the effect of precursor preparation on film formation is critical to achieve high‐quality perovskite film and, therefore, high efficiency in related solar devices. Herein, the two methods to prepare phenethylammonium‐based mixed perovskite precursors with the same chemical composition are reported. These methods are called 1) different phase (DP) and 2) same phase (SP) methods as the former involves the mixing of a 3D perovskite precursor with a 2D perovskite precursor, whereas the latter involves the mixing of quasi‐2D perovskite precursors. The films prepared by these methods are characterized by X‐ray diffraction, Kelvin probe force microscopy, and scanning electron microscopy, revealing different perovskite structures. The power conversion efficiency (PCE) of the champion cells by DP and SP methods reaches 19.1% and 18.9%, respectively. Results of the aging test show a dramatic improvement in the stability of SP perovskite devices maintaining 86% of its initial performance after exposure to a relative humidity (RH) 8 ± 5% for 1000 hr and over 80% of its initial PCE after continuous 1 sun illumination (including UV) at RH 70%. The new insights provided by this work are important to design perovskite precursor preparation methods for the best device performance and stability.

Achieving Resistance against Moisture and Oxygen for Perovskite Solar Cells with High Efficiency and Stability

“…Another method called the same phase method achieved decent stability under a high humidity environment by f a b r i c a t i n g q u a s i -2 D P E A 2 F A n − 1 P b n I 3 n + 1 a n d PEA 2 MA n−1 Pb n Br 3n+1 separately and then mixing them together into perovskite. 117 The reason for the high stability is that there is no formation of a different phase when the hydrophobic phenethylammonium (PEA) is incorporated into the perovskite, fostering a uniform perovskite film. The other method named self-seeding growth was developed to bolster a longer time moisture stability of PSCs (Figure 5c).…”

“…Adopting appropriate solution-based methods to reduce the defects and improve perovskite film quality (Figure a) fosters better moisture and oxygen stability. − It was reported that 93% retention of original PCE of 20.63% was realized under 40% humidity after 500 h for PSC fabricated by a dropwise addition method, which included two steps: the PbI 2 film was first deposited and then the FA/MA iodide with isopropanol (IPA) and dimethyl sulfoxide (DMSO) was introduced dropwise (Figure b) . Carefully controlling the dropwise addition process resulted in highly compact and flat surface and larger crystal size with well-packed crystals, substantially mitigating GBs and defect states, increasing light absorption, and inhibiting carrier recombination.…”

“…This result implies that the dropwise addition method is an effective way to prepare large-grain perovskite films and raise both efficiency and moisture stability by reducing defects. Another method called the same phase method achieved decent stability under a high humidity environment by fabricating quasi-2D PEA 2 FA n –1 Pb n I 3 n +1 and PEA 2 MA n –1 Pb n Br 3 n +1 separately and then mixing them together into perovskite . The reason for the high stability is that there is no formation of a different phase when the hydrophobic phenethylammonium (PEA) is incorporated into the perovskite, fostering a uniform perovskite film.…”

“…(a) Effect of solution-based process methods on efficiency and stability. − (b) Schematic process of PSCs by the dropwise addition method. Reproduced with permission from ref .…”

The Key Role of Hole Transport Layer in Boosting Performance of Two‐Dimensional Perovskite Solar Cells

“…Due to the introduction of large cations, there is a heterogeneous distribution of various n phases in 2D perovskite (Figure 3c), [108] ITO/SnO 2 /PVK/Spiro-OMeTAD/Ag (TMA) 2 FA 4 Pb 5 I 16 1.15 79 22.15 20.12 2021 [109] (ITO)/NiOx/PVK/PCBM (50 wt% ICBA)/BCP/Ag BA 2 MA 2 Pb 3 I 10 1.23 72.17 13.61 12.07 2018 [67] ITO/Cu:NiOx/PVK/PCBM/BCP/Ag (TEA) 2 (MA) 2 Pb 3 I 10 1.23 75.3 15.85 14.68 2020 [110] ITO/PEDOT:PSS/PVK/PCBM/BCP/Ag BA 2 MA 4 Pb 5 I 16 1.1 77 16.74 14.09 2019 [111] ITO/PEDOT:PSS/PVK/PCBM/BCP/Ag (ThMA) 2 (FA) holes can spontaneously transfer from the high n phase to the low n phase in the gradient phase distribution, and the electrons move in the opposite direction, as shown in Figure 3b. [30] Significant directional changes in mobility and conductivity are seen in 2D perovskite; these differences are more pronounced in the direction of the inorganic plate than in the perpendicular to the inorganic plate.…”