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• Past decade has witnessed an earthshaking efficiency progress for 3D perovskites [1,2]. However, because the poor chemical stability of the 3D perovskite, it is easy to degrade under environmental conditions such as, oxygen, humidity and high temperature, which greatly hinders their commercialization process [3,4]. 2D metal halide perovskites presenting remarkable environmental stability suitable for practical application have given rise to tremendous interest and making this magic material a rising star in photovoltaic technologies.

  Depending on the type of introduced organic spacer cations, 2D perovskites can form Ruddlesden-Popper (RP), Dion-Jacobson (DJ), and alternating cations interlayer (ACI) phase three different types [5]. Among them, 2D RP perovskites of BA₂(MA)_n-1Pb_nI_3n+1 series (BA series) are considered to be the most promising and potential layered materials due to their superior environmental stability and favorable reproducibility [5,6]. The PCE of BA series materials (n ≤ 5) has experienced a remarkable increase in recent years [7,8]. However, BA series 2D perovskite materials encounter two challenges that affect their device performance. One is inefficient light absorption and the other is the presence of low n phases [9,10]. The low n phases are poorly conductive and act as a carrier trap, resulting in lower efficiency devices [9,11]. For the issue of inefficient light absorption, Chen et al. reported double A-site cation 2D perovskite for the first time, achieving an ideal band gap of 1.51 eV [12]. Unfortunately, they achieved only 6.88% PCE due to poor film quality. Later, Shao et al. incorporated guanidinium (GA⁺) into PEA-based RP 2D perovskite fabricating a mixed bulky (PEA, GA)₂MA₄Pb₅I₁₆ 2D perovskite [13]. They found that the incorporating GA⁺ not only enhanced the light absorption of 2D perovskite, but also promoted the carrier transport inside the 2D perovskite film. Although many other efforts have been made to reduce the band gap of 2D RP perovskites, the relatively low efficiency produced by inappropriate n value choosing has limited their further development [14,15]. To the issue of disordered phase distribution, Lee et al. found that addition of DMSO in DMF solvent can reduce the intensity of low n phases, thereby reducing carrier recombination centers and improving device performance [11]. Then, Xu et al. found 2D perovskite (BA, OA)₂(MA, FA)₂Pb_nI_3n+1 (n = 4) with OA cation exhibits enhanced charge transport due to inhibition of low n phases [16]. To realize better carrier transport, in 2020, Liu et al. reported a synergistic effect and found optimization of solvent ratio and substrate preheating temperature can gradually reduce the intensity of low n phases [17]. Though better charge transport was achieved within 2D perovskites through regulate the phase distribution, the efficiency is still far from satisfactory since the low n phases is only suppressed rather than eliminated.

  In this work, we combine the introduction of FA and the addition of PbCl₂ fabricated FA/MA mixed BA₂(MA_1-xFA_x)₄Pb₅I_3n+1 (n = 5) layered perovskites. This method avoids the issue of poor film quality caused by inappropriate n value selection and completely eliminates the existence of low n phase of n = 1. In comparison with the FA-free 2D perovskite film, the optimal FA-based film exhibits improved crystallinity and enhanced light absorption, achieving a higher J_SC of 20.01 mA/cm² than the FA-free sample of 17.86 mA/cm². After further addition of PbCl₂ in the optimal FA/MA mixed precursor solution, we observed that the low n phase of n = 1 was fully eliminated and the low n phase of n = 2 was noticeably suppressed. In addition, the PbCl₂-added 2D perovskite exhibits micron-level grain size (1.83 µm) with enhanced film crystallinity. Importantly, the PbCl₂-added 2D perovskite film displays higher surface contact potential, reduced trap density, and superior carrier transport, thus a high PCE of 16.48%. The optimal PbCl₂-added BA₂(MA_0.95FA_0.05)₄Pb₅I₁₆ film and device also display superior environmental stability after storage in an average humidity of 57% ± 3%.

  The BA₂(MA)₄Pb₅I₁₆ (control) film was prepared by one-step hot-casting method using (BAI), methyl ammonium iodide (MAI) and lead iodide (PbI₂) as raw materials and DMF/DMSO as a binary solvent. As discussed in the introduction, cation FA was employed to partially replace cation MA in BA₂(MA)₄Pb₅I₁₆ material aiming to obtain a band gap moderate mixed A site cation 2D perovskites. The amount of FA is determined according to the components of BA₂(MA_1-xFA_x)₄Pb₅I₁₆ (x = 0, 0.05, 0.10, 0.20, 0.40). For the prepared BA₂(MA_1-xFA_x)₄Pb₅I₁₆ series, some targeted characterizations were conducted to investigate the effect of FA introduction on the 2D perovskite films.

  First, we carried out X-ray diffraction (XRD) and ultraviolet absorption spectrum (UV) to investigate the structure variation and light absorption case upon the introduction of cation FA. Fig. 1a represents XRD patterns of different amount of FA introduced 2D perovskite films. All films display (111) and (202) character diffraction peaks of 2D perovskite in 14.1° and 28.3° [19,20]. After the introduction of FA, the diffraction peak shifted to the lower diffraction angles, indicating that FA/MA layered 2D perovskite was successfully processed [10,21]. It is worth mentioning that the full-width at half-maximum (FWHM) value of (111) and (202) two diffraction peaks gradually decrease as the increasing of FA ratio (Fig. 1b), confirming increased crystal size and improved crystallinity. Note that low angle diffraction peak appeared when the FA content was higher than 0.05. We speculate that this could be ascribed to the formation of BA₂FAPb₂I₄ (low n phase) perovskite owing excess FA introduction. The low n phase has the drawbacks of a large band gap, poor conductivity, and mismatched energy band structure [5,22,23], which is not conducive to device performance. We observed that after the introduction of FA, the absorption of 2D perovskite film enhanced first and then attenuated (Fig. 1c). The optimal FA/MA mixed 2D perovskite film (0.05 FA) exhibits absorption edge red-shifts in comparison with the control film, from 646 nm to 659 nm. This result demonstrates that the addition of FA indeed reduced the optical band gap and enhanced the light absorption. The PL results of different FA contents introduced 2D perovskite films are shown in Fig. 1d. As increasing FA ratio from 0.05 to 0.40, PL peak displayed red-shift (0.05FA) and then blue-shift (FA > 0.05), which is due to the formation of low n phase of 2D perovskites after FA content was higher than 5%. The performance statistics distribution for different amounts of FA-introduced devices is shown in Fig. S1a (Supporting information). It is observed that the optimal FA replacement amount is 0.05, and the device efficiency decreases when it is higher than 0.05. The corresponding J-V curves and device parameters are displayed in Fig. S1b and Table S1 (Supporting information). The average value of the J_sc increased from 17.76 mA/cm² to 19.70 mA/cm² for FA-free and FA-introduced 2D perovskite devices. The performance improvement after the introducing cation FA may arise from the enhancement of light absorption due to the extending of the absorption range.

  Figure 1

  

  Figure 1.  (a) XRD diffraction results of different FA content-based-2D perovskite films. (b) The (111) and (202) half-peak width values of 2D perovskite films at different contents of FA ratios. (c, d). UV–vis absorption and PL spectra of different FA content based-2D perovskite films.

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  We further introduced PbCl₂ to regulate the crystallization process of 2D perovskite to improve the film quality and device performance. Fig. 2a exhibits the PL spectra of 2D perovskite films after the addition of different molar ratios of PbCl₂. The resultant 2D perovskite displays multiple perovskite phases, indicating a multiphase mixed structure. Meanwhile, we observed that after the addition of PbCl₂, the peak intensity of the 3D perovskite gradually decreases, revealing the holes and electrons are easily separated and extracted in PbCl₂-introduced 2D perovskite films [24,25]. It is worth noting that when the PL spectrum is locally amplified (500–675 nm), we found that the addition of 1.5 mol% PbCl₂ (PbCl₂-added) eliminated the low n phase of n = 1 and suppressed the formation of low n phase of n = 2 (Fig. 2b). This result demonstrates that the addition of PbCl₂ effectively regulated the crystallization growth process and crystallization kinetics of layered low dimensional perovskite. Based on the above results, we propose the schematic diagrams (Fig. 2c) of the phase distribution of PbCl₂-free and PbCl₂-added perovskite. Owing to containing fewer low-n phases, PbCl₂-added 2D perovskite promotes internal carrier transport, which is conducive to improving device performance [11,16].

  Figure 2

  

  Figure 2.  (a) PL spectra of 2D perovskite films at different molar ratios of PbCl₂ (excited from perovskite back side). (b) Locally amplified PL results (500–675 nm). (c) Phase distribution schematic diagrams of PbCl₂-free and PbCl₂-added 2D perovskites.

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  After studying the phase distribution of 2D perovskite at different molar ratios of PbCl₂, atomic force microscope (AFM) was performed for PbCl₂-free and PbCl₂-added layered low dimensional perovskite films (Fig. 3a). The PbCl₂-free 2D perovskite film shows small grain size and uneven grain size distribution, with a root-mean-square roughness (RMS) of 18.9 nm. However, the PbCl₂-added 2D perovskite exhibits larger grain size and uniform grain size distribution, with an RMS value of 18.5 nm. This result demonstrates that the introduction of PbCl₂ can delay the precipitation of FA/MA mixed supersaturated precursor solution, and is conducive to forming crystal grains with larger size due to the decreasing of nucleation sites [26]. Meanwhile, this result also verifies again that the addition of PbCl₂ indeed regulates the crystallization growth process and crystallization kinetics of 2D perovskite. Fig. 3b displays the grain size statistics of PbCl₂-free and PbCl₂-added 2D perovskite films. The PbCl₂-added 2D perovskite has an average grain size of 1.83 µm dramatically larger than the PbCl₂-free sample, which can be seen more clearly from the supplementary material (Fig. S2 in Supporting information). The increased grain size implies improved crystallinity and reduced grain boundary of FA/MA mixed 2D perovskite, which can greatly promote carrier transport within the 2D perovskite [27]. Fig. S3 (Supporting information) exhibits corresponding SEM images, both the PbCl₂-free and PbCl₂-added film showed uniform and complete surface coverage.

  Figure 3

  

  Figure 3.  (a) AFM images of PbCl₂-free and PbCl₂-added 2D perovskites. (b) 2D perovskite grain size statistics based on AFM results.

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  To gain a deeper understanding of the underlying physics behind charge carrier transport in PbCl₂-added 2D perovskites, the photoelectric properties of the PbCl₂-free and PbCl₂-added perovskite films were systematically characterized. Figs. 4a and b exhibit the kelvin probe force microscopy (KPFM) images of the PbCl₂-free and PbCl₂-added 2D perovskites. Potential variations from ≈ −322 mV to −94 mV were observed for PbCl₂-free 2D perovskite film, while it was enhanced to ≈−0.084 mV to 0.0967 mV for PbCl₂-added perovskite film. Meanwhile, the surface potential of PbCl₂-added 2D perovskite films exhibits enhanced uniformity compared to those PbCl₂-free samples (Fig. 4c). In addition, after addition of PbCl₂, the average values of the surface potentials increased from −207 mV to 11.2 mV, indicating that 1.5 mol% PbCl₂ addition promotes the separation and transportation of charge carriers within the perovskite film [28]. Time-resolved photoluminescence (TRPL) spectra (Fig. 4d) reveal that PbCl₂-added 2D perovskite film displays a longer average carrier lifetime of τ = 11.72 ns than τ = 3.80 ns for PbCl₂-free sample, specific attenuation parameters τ₁ and τ₂ are listed in Table S2 (Supporting information). Enhanced carrier lifetime suggested that the addition of PbCl₂ suppressed carrier recombination and improved the film quality [29,30]. Meanwhile, alternating current impedance spectroscopy measurements are conducted, corresponding Nyquist plots results shown in Fig. 4e. The recombination resistance (R_rec) was dramatically increased from 1433 Ω (without PbCl₂) to 1837 Ω for the PbCl₂-added device implying that the addition of PbCl₂ inhibit carrier recombination inside the perovskite film [31], specific resistance parameters are shown in Table S3 (Supporting information). Based on the above analysis, we can conclude that the introduction of PbCl₂ promotes carrier transport, reduces defect density, and suppresses carrier recombination within the perovskite film. These results demonstrate that PbCl₂ is a resultful additive to improve the quality of layered low dimensional perovskite films.

  Figure 4

  

  Figure 4.  (a, b) KPFM images of PbCl₂-free and PbCl₂-added perovskite film. (c) Surface contact potential differences (CPD) distribution statistics. (d, e) Corresponding TRPL spectra and Nyquist plots.

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  To further investigate the charge-carrier physics in PbCl₂-added 2D perovskite films, incident light intensity dependence of V_OC, dark J-V curves, and motte-schottky curves were performed. Light intensity-dependent V_OC is demonstrated to correlate with the charge recombination loss in the usage of the devices [32]. As shown in Fig. 5a, according to the fitting result, the PbCl₂-added solar cell has a V_OC versus P_light slope of 0.947kT/q, which is much smaller than the PbCl₂-free sample of 1.16kT/q, where k is Boltzmann’s constant, T is temperature, and q is elementary charge. This result suggests that trap-assisted recombination is noticeably suppressed in the PbCl₂-added devices [33]. Fig. 5b is the dark J-V curves of 2D perovskite devices. The PbCl₂-added device produces a lower dark current of 2.74 × 10⁻³ mA/cm² than the PbCl₂-free one (2.21 × 10⁻² mA/cm²), indicating less trap states in the PbCl₂-added devices [34]. Space-charge-limited current (SCLC) method was used to quantitatively describe the trap density within the 2D perovskite for PbCl₂-free and PbCl₂-added hole-only devices (ITO/NiOx/2D perovskite/Spiro-OMeTAD/Ag). The fitting results are shown in Fig. 5c. According to the formula of N_trap = 2εε₀V_TFL/qL² [35], where ε_r is the relative dielectric constant (ε_r = 25), ε₀ is the vacuum permittivity, q is the elemental charge, and L is the thickness of the photo-absorber layer (600 nm), the PbCl₂-added device delivers a lower trap density of 2.05 × 10¹⁵ cm⁻³ than the PbCl₂-free sample of 3.71 × 10¹⁵ cm⁻³. This result suggested that the addition of PbCl₂ can effectively reduce the trap density within the perovskite films, thus reducing non-radiative recombination and improving film quality. To further investigate the effect of PbCl₂ addition on the carrier transport, we conducted the Motte-Schottky curve (Fig. 5d). The PbCl₂-added device generates a built-in electric field (V_bi) of 0.814 V noticeably higher than the PbCl₂-free sample of 0.633 V, which indicates that the addition of PbCl₂ drives the separation and transport of photogenerated carriers [18]. These results indicate that the addition of PbCl₂ efficaciously reduces the defect density in perovskite films, thereby facilitating carrier separation and transport within the films.

  Figure 5

  

  Figure 5.  (a) Incident light intensity dependence of V_OC for PbCl₂-free and PbCl₂-added devices. (b, c) Dark J-V curves for PbCl₂-free and PbCl₂-added devices. (d) Corresponding Mott-Schottky plots.

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  To verify the photovoltaic performance of PbCl₂-free and PbCl₂-added devices, inverted planar PSCs were fabricated with a device architecture of indium tin oxide (ITO) /NiO_x/2D perovskite /PCBM/BCP/Ag. Fig. S4 (Supporting information) exhibits the efficiency distribution diagram of perovskite cells with different content of PbCl₂. After adding 1.5 mol% PbCl₂, 2D perovskite showed the optimal efficiency. Table 1 displays the champion and average (Ave) device parameters of PbCl₂-free and PbCl₂-added solar cells (forward scan). The PbCl₂-free sample shows an average PCE of 14.77%, V_oc of 1.11 V, J_SC of 19.41 mA/cm², FF of 69.8%, a highest V_oc of 1.16 V, FF of 75.53%, a decent PCE of 15.72%. After addition of 1.5 mol% PbCl₂ into the optimal FA-based 2D perovskite precursor, the average PCE was enhanced to 15.46%, FF to 70.5%, achieving a highest PCE of 16.48%. The enhanced PCE performance is ascribed to the effective phase regulation of 2D perovskite by the addition of PbCl₂. Fig. 6a exhibits the EQE spectrum of the PbCl₂-free and PbCl₂-added champion devices. The J_SC integrated from the incident photon to current conversion efficiency (IPCE) spectra was 17.41 mA/cm² and 18.32 mA/cm² for the PbCl₂-free and PbCl₂-added solar cell, analogously matching (< 5% discrepancy) well with the value derived from the J-V curves (Fig. 6b). This result confirms the increased device performance, because of the effective phase regulation and improved charge transport.

  Table 1

  

  Table 1.  Device parameters of PbCl₂-free and PbCl₂-added solar cells.

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  Figure 6

  

  Figure 6.  (a) EQE spectrum of the PbCl₂-free and PbCl₂-added champion devices. (b) Corresponding J-V curves (forward scan). (c, d) XRD aging test results of PbCl₂-free and PbCl₂-added layered perovskite films at an average humidity of 57% ± 3%. (e) Corresponding photovoltaic device humidity resistance results.

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  To verify the impact of chloride additive on the stability of layered 2D perovskite, the fabricated film and unencapsulated 2D photovoltaic devices were placed in a harsh atmosphere with an average humidity of 57% ± 3%. For the PbCl₂-free sample, the peak intensity of (111) and (202) diffraction planes markedly decreased after 60 days of storage (Fig. 6c), which reflected poor humidity stability. Nevertheless, as shown in Fig. 6d, the PbCl₂-added 2D perovskite film displays completely unchanged peak strength. Meanwhile, as shown in Fig. 6e, the PbCl₂-added 2D perovskite solar cell exhibits relatively higher moisture stability in comparison with the PbCl₂-free sample after storage of more than 800 h in air. These results show that the addition of PbCl₂ significantly enhances the humidity resistance of layered perovskite films and devices, which may be due to the reduction of defects and the improvement of film quality after the addition of PbCl₂. We tested the champion PbCl₂-added 2D perovskite device from different scanning directions (Fig. S5 in Supporting information). The resultant PbCl₂-added 2D perovskite solar cell displays ignorable hysteresis (less than 5%). The improved stability and negligible hysteresis confirmed again that the addition of PbCl₂ has a benign effect on 2D perovskite films, which is conducive to improving the device performance.

  Mix cation BA₂(MA_0.95FA_0.05)₄Pb₅I₁₆ perovskite films were successfully prepared by introducing cation FA to replace cation MA. The incorporation of FA strengthened the light absorption range and enhanced the crystallinity of 2D perovskite contributing to notably improved J_SC. After further introduction of PbCl₂, the low n phase of n = 1 was eliminated and the low n phase of n = 2 was notably suppressed. Meanwhile, the addition of PbCl₂ promoted the formation of 2D perovskite films with large grain size and less defect density, which greatly facilitated the carrier transport within the 2D perovskite film. Importantly, the PbCl₂-added layered perovskite film and device show significantly enhanced moisture stability in contrast to the PbCl₂-free sample. The synergistic effect of A-site cation engineering and phase regulation achieves an impressive PCE of 16.48%. Our results highlight a promising future of efficient and sTable 2D PSCs toward commercialization.

  Declaration of competing interest

  The authors declare no conflict of interest.

  Acknowledgments

  This work financially supported by the Chengdu Science and Technology Program (No. 2021GH0200032HZ), and Sichuan Engineering Technology Research Center of Basalt Fiber Composites Development and Application (No. 2022SCXWYXWFC006), and Natural Science Foundation of Sichuan Province (No. 2022NSFSC0356).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.109545.

  
  
• 1. [1]

     J. Xu, J. Chen, S. Chen, et al., Chem. Eng. J. 453 (2023) 139790. doi: 10.1016/j.cej.2022.139790

  2. [2]

     J. Xu, H. Chen, L. Grater, et al., Nat. Mater. 23 (2023) 23450.

  3. [3]

     H. Peng, D. Li, Z. Li, et al., Nanomicro Lett 15 (2023) 91.

  4. [4]

     H. Zheng, D. Liu, Y. Wang, et al., Chem. Eng. J. 389 (2020) 124266. doi: 10.1016/j.cej.2020.124266

  5. [5]

     R. Liu, X. Hu, M. Xu, et al., ChemSusChem 16 (2023) e202300736. doi: 10.1002/cssc.202300736

  6. [6]

     P. Liu, N. Han, W. Wang, et al., Adv. Mater. 33 (2021) e2002582. doi: 10.1002/adma.202002582

  7. [7]

     H. Tsai, W. Nie, J.C. Blancon, et al., Nature 536 (2016) 312–316. doi: 10.1038/nature18306

  8. [8]

     W. Kong, F. Zeng, Z. Su, et al., Adv. Energy Mater. 12 (2022) 202704.

  9. [9]

     J. Liang, Z. Zhang, Q. Xue, et al., Energy Environ. Sci. 15 (2022) 296–310. doi: 10.1039/D1EE01695D

  10. [10]

      M. Shao, T. Bie, L. Yang, et al., Adv. Mater. 34 (2022) e2107211. doi: 10.1002/adma.202107211

  11. [11]

      C. Ma, M.F. Lo, C.S. Lee, et al., J. Mater. Chem. A 6 (2018) 18871–18876. doi: 10.1039/C8TA06976J

  12. [12]

      J. Yan, W. Fu, X. Zhang, et al., Mater. Chem. Front. 2 (2018) 121–128. doi: 10.1039/C7QM00472A

  13. [13]

      J. Shi, X. Jin, Y. Wu, et al., APL Mater. 8 (2020) 101102. doi: 10.1063/5.0024135

  14. [14]

      L. Gao, F. Zhang, X. Chen, et al., Angew. Chem. Int. Ed. 58 (2019) 11737–11741. doi: 10.1002/anie.201905690

  15. [15]

      M. Long, T. Zhang, D. Chen, et al., ACS Energy Lett. 4 (2019) 1025–1033. doi: 10.1021/acsenergylett.9b00351

  16. [16]

      J. Meng, D. Song, D. Huang, et al., Phys. Chem. Chem. Phys. 22 (2019) 54–61.

  17. [17]

      R. Liu, H. Li, F. Zhang, et al., Solar Energy 209 (2020) 446–453. doi: 10.1016/j.solener.2020.09.006

  18. [18]

      R. Liu, Y. Yu, C. Liu, et al., Sci. China Chem. 65 (2022) 2468–2475. doi: 10.1007/s11426-022-1349-6

  19. [19]

      R. Liu, Y. Yu, T. Hu, et al., J. Power Sources 512 (2021) 230452. doi: 10.1016/j.jpowsour.2021.230452

  20. [20]

      S. Tan, N. Zhou, Y. Chen, et al., Adv. Energy Mater. 9 (2018) 1803024.

  21. [21]

      Y. Yu, R. Liu, F. Zhang, et al., J. Colloid Interface Sci. 605 (2022) 710–717. doi: 10.1016/j.jcis.2021.07.147

  22. [22]

      D.H. Cao, C.C. Stoumpos, O.K. Farha, et al., J. Am. Chem. Soc. 137 (2015) 7843–7850. doi: 10.1021/jacs.5b03796

  23. [23]

      B. Traore, L. Pedesseau, L. Assam, et al., ACS Nano 12 (2018) 3321–3332. doi: 10.1021/acsnano.7b08202

  24. [24]

      J. Zhang, H. Luo, W. Xie, et al., Nanoscale 10 (2018) 5617–5625. doi: 10.1039/C7NR08750K

  25. [25]

      W. Chen, Y. Zhou, G. Chen, et al., Adv. Energy Mater. 9 (2019) 1803872. doi: 10.1002/aenm.201803872

  26. [26]

      C. Bi, Q. Wang, Y. Shao, et al., Nat. Commun. 6 (2015) 7747. doi: 10.1038/ncomms8747

  27. [27]

      Y. Wang, J. Wu, P. Zhang, et al., Nano Energy 39 (2017) 616–625. doi: 10.1016/j.nanoen.2017.07.046

  28. [28]

      L. Zhu, X. Zhang, M. Li, et al., Adv. Energy Mater. 11 (2021) 2100529. doi: 10.1002/aenm.202100529

  29. [29]

      H. Yu, Y. Xie, J. Zhang, et al., Adv. Sci. 8 (2021) 2004510. doi: 10.1002/advs.202004510

  30. [30]

      Y. Yu, R. Liu, C. Liu, et al., Adv. Energy Mater. 12 (2022) 2201509. doi: 10.1002/aenm.202201509

  31. [31]

      G. Wu, J. Zhou, J. Zhang, et al., Nano Energy 58 (2019) 706–714. doi: 10.1016/j.nanoen.2019.02.002

  32. [32]

      H. Lai, D. Lu, Z. Xu, et al., Adv. Mater. 32 (2020) e2001470. doi: 10.1002/adma.202001470

  33. [33]

      X. Lian, H. Wu, L. Zuo, et al., Adv. Funct. Mater. 30 (2020) 2004188. doi: 10.1002/adfm.202004188

  34. [34]

      W. Ke, C. Chen, I. Spanopoulos, et al., J. Am. Chem. Soc. 142 (2020) 15049–15057. doi: 10.1021/jacs.0c06288

  35. [35]

      D. Lu, G. Lv, Z. Xu, et al., J. Am. Chem. Soc. 142 (2020) 11114–11122. doi: 10.1021/jacs.0c03363

• 

  Figure 1  (a) XRD diffraction results of different FA content-based-2D perovskite films. (b) The (111) and (202) half-peak width values of 2D perovskite films at different contents of FA ratios. (c, d). UV–vis absorption and PL spectra of different FA content based-2D perovskite films.

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  Figure 2  (a) PL spectra of 2D perovskite films at different molar ratios of PbCl₂ (excited from perovskite back side). (b) Locally amplified PL results (500–675 nm). (c) Phase distribution schematic diagrams of PbCl₂-free and PbCl₂-added 2D perovskites.

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  Figure 3  (a) AFM images of PbCl₂-free and PbCl₂-added 2D perovskites. (b) 2D perovskite grain size statistics based on AFM results.

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  Figure 4  (a, b) KPFM images of PbCl₂-free and PbCl₂-added perovskite film. (c) Surface contact potential differences (CPD) distribution statistics. (d, e) Corresponding TRPL spectra and Nyquist plots.

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  Figure 5  (a) Incident light intensity dependence of V_OC for PbCl₂-free and PbCl₂-added devices. (b, c) Dark J-V curves for PbCl₂-free and PbCl₂-added devices. (d) Corresponding Mott-Schottky plots.

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  Figure 6  (a) EQE spectrum of the PbCl₂-free and PbCl₂-added champion devices. (b) Corresponding J-V curves (forward scan). (c, d) XRD aging test results of PbCl₂-free and PbCl₂-added layered perovskite films at an average humidity of 57% ± 3%. (e) Corresponding photovoltaic device humidity resistance results.

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  Table 1.  Device parameters of PbCl₂-free and PbCl₂-added solar cells.

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