Formamidinium-Based Perovskite Solar Cells with Enhanced Moisture Stability and Performance via Confined Pressure Annealing

Abstract

Formamidinium (FA)-based perovskite solar cells (PSC) show enhanced stability compared to their methylammonium (MA)-based counterparts. However, their stability needs to be further enhanced for the potential commercial applications. We demonstrate here that the high-quality thin film can be obtained for the FA-based perovskite with remarkably enhanced moisture stability using a confined-pressure annealing (CPA) processing and controlling the amount of Cs introduced into the FAPbI 3 perovskite precursor solution. Without additional 2D cation additives, surface passivation, or encapsulation, no phase degradation was observed for the Cs 0.1 FA 0.9 PbI 3 perovskite under a humidity of 70% RH for over 500 h. The unencapsulated device maintained over 70% performance for 500 h compared to <80 h of the conventional processed devices, which is comparable to the outstanding moisture stability of the 2D/3D perovskites. The FAbased perovskite grain size was promoted to over 1 μm with a high static water contact angle up to 112°. The surface cation composition was varied with the concentrated FA cation species at the surface while homogenized Cs/FA distribution inside the film. The trapped-state density and carrier recombination rate were also reduced with a high fill factor of 82% and an efficiency over 20.23%. This work suggests that the intrinsic stability of the 3D perovskite could be further enhanced by adjusting the surface compositions during the crystallization process.

Chlorobenzenesulfonic Potassium Salts as the Efficient Multifunctional Passivator for the Buried Interface in Regular Perovskite Solar Cells

“…In addition, an obviously increased photoluminescence (PL) intensity was obtained in the SnO 2 /3Cl‐BSAK‐based perovskite films compared to the reference perovskite films (Figure 3c), which reveals the higher crystallinity and fewer irradiative recombination center defects. [ 52 ] The crystallization of perovskite films based on SnO 2 ETL and modified ETLs was investigated by X‐ray diffraction (XRD). As shown in Figures 3d and Figure S9 (Supporting Information), the intensity of the perovskite XRD peak based on SnO 2 /3Cl‐BASK was enhanced, while the positions of the characteristic diffraction peaks are essentially the same for all the perovskite films, indicating an improvement in the crystallization without the observable lattice parameter changed.…”

“…As shown in the Figure 4c, the linear region at the low bias voltage corresponds to the ohmic response, then increasing in current injection as the bias voltage increases, considered to be the trap‐filling process. [ 25 ] The intersection between these two regions is defined as the trap‐filling limit voltage ( V TFL ), and the electron defect density in a perovskite device can be calculated according to the following equation [ 52 ] where e is the unit charge, n t denotes the corresponding defect density, L is the thickness of the perovskite films, ε 0 and ε represents the vacuum dielectric constant and the relative dielectric constant of perovskite, [ 30 ] respectively. After modified the SnO 2 with 3Cl‐BSAK, the defect density of perovskite film is significantly reduced from 5.57×10 15 to 1.77×10 15 cm –3 (Table S6, Supporting Information), which should be attributed to the improved quality of the perovskite films and the ameliorative interface contact between the perovskite layer and ETL.…”

Efficient and Stable FA‐Rich Perovskite Photovoltaics: From Material Properties to Device Optimization

“…Unencapsulated cells MPP at 65 °C in N 2 for 400 h, drop by ≈12% 2020 [30] Cs 0.1 FA 0.9 PbI 3 20.23 Strain engineering _ _ Unencapsulated cells stored at 70% RH for 500 h, drop by <30% _ 2020 [31] Cs 0.17 FA 0.83 PbI 3 23.35 Crystal growth Unencapsulated cells aged at 85 °C and 15 ± 5% RH in the air for 500 h, drop by ≈20% _ _ _ 2021 [32] Cs x FA 1-x PbI 3 21.98 Crystal growth _ _ _ _ 2021 [33] Cs 2019 [42] FA 0.57 MA 0.43 PbI 2.87 Br 0.13 21.21 (Certified) Crystal growth _ _ _ _ 2019 [43] (FAPbI 3 ) x (MAPbBr 2019 [44] (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 20.7 (Certified) Strain engineering _ _ _ _ 2019 [45] (FAPbI 3 ) 0.95 (MAPbBr 2019 [46] (FAPbI 3 ) 0.97 (MAPbBr 2021 [47] (FAPbI 3 ) 0.97 (MAPbBr 2021 [48] (FAPbI 3 ) 0.94 (MAPbBr 2021 [49] (FAPbI 3 ) 0.95 (MAPbBr 2021 [50] (FAPbI 3 ) 0.9 (MAPbBr 3 ) 0.1 25.2 (Certified) Interface engineering _ _ Encapsulated cells stored at 30% RH for 3600 h, no drop _ 2021 [51] Cs 0.05 FA 0.81 MA 0. 2019 [52] 2019 [53] (Cs,FA,MA)Pb(I,Br) 3 20.87 (Certified) Additive Stored in N 2 for 1500 h, drop by ≈10% _ 2019 [54] Cs 0.07 FA 0.9 MA 0.03 Pb(I 0.92 Br 0.08 ) 2019 [55] Cs 0.05 (FA 0.92 MA 0.08 ) 0.95 Pb(I 0.92 Br 0.08 ) 3 22.3 (Certified) Crystal growth _ _ _ MPP with 420-nm UV filter in N 2 for 1000 h, no drop 2020 [56] Cs _ 2020 [57] (Cs,FA,MA)Pb(I,Br) 3 23.3 (Certified) Crystal growth _ _ _ _ 2020 [58] (Cs,FA,MA)Pb(I,Br) _ 2021 [62] Cs 2021 [63] Cs _ 2021 [66] Table 1.…”

Design Principles of Large Cation Incorporation in Halide Perovskites

“…A common approach to remaining within the bandgap range of pristine lead halide perovskites has been the partial incorporation of the cations. Interestingly, there are recent reports that demonstrate a promising route of the commercialization of halide perovskite solar cells light absorbers based on formamidinium (FA) and a mixture of other cations [ 25 , 26 , 27 ]. In addition to MA and FA, there are other commonly used monovalent cations such as ethylammonium (EA), guanidinium (GUA), hydrazinium (HZ), and hydroxylammonium (HA) [ 28 , 29 ].…”