Structure, Morphology, and Photovoltaic Implications of Halide Alloying in Lead‐Free Cs₃Sb₂Cl_xI_9–x 2D‐Layered Perovskites

Abstract

Lead-based perovskites have benefitted immensely from compositionally tuning away from methylammonium lead iodide (MAPbI 3), giving rise to record-breaking power conversion efficiencies (PCEs), impressive device stabilities, and broadly tunable optoelectronic properties suitable for a vast range of useful applications. [1-8] However, there is currently significant motivation to pursue lead-free perovskite derivatives for a number of reasons that extend beyond the manufacturing and environmental concerns associated with Pb. [9-11] Group 15 metals, such as arsenic, bismuth, and antimony, have shown promise as alternates to Pb outside of Group 14. [12-15] An unavoidable consequence of replacing Pb 2þ with a pnictogen-like Sb 3þ , for example, is that the general AMX 3 perovskite formula transforms to one of their derivatives such as A 3 M 2 X 9 , where A and M are, respectively, monovalent cations (organic/ inorganic) and a metal cation, whereas X predominantly represents halogen anions. There are multiple perovskite derivative substructures accessible to the A 3 M 2 X 9 formula: one is the 0D (dimer) phase with isolated A 2 X 3 9À bioctahedra, and the other is the 2D phase with continuous corrugated layers of polyanions. [16,17] This fact has presented a challenge for researchers seeking to understand and improve these lead-free alternatives for use in solar energy conversion. Due to the large indirect bandgap (2.2-2.5 eV) and poor carrier transport associated with the isolated nature of the 0D polymorph, [18] many groups have focused on targeting the 2D-layered phase, which has a high absorption coefficient, a bandgap on the order of %2 eV, and a comparatively small effective mass in both in-plane and out-of-plane directions, making it the more suitable choice for energy harvesting. [16,19] For this reason, the majority of all-inorganic lead-free perovskite research to date has focused on circumventing the 0D phase to preferentially form the 2D phase, or, to simplify the film fabrication process by achieving the 2D phase at lower temperatures in solution. To date, there has been a lack of focus on the intrinsic photophysics at play as a function of compositional tuning for a fixed substructure. In this article, we will show how photoinduced charge carrier generation, recombination, lifetime, and transport all change within a fixed 2D polymorph of Cs 3 Sb 2 I 9 as a function of alloying Cl À at the X-site, and ultimately how this improves its performance in a solar cell. All-inorganic (Cs þ rather than MA þ at the A-site, for example) Sb-based perovskite derivatives have attracted significant recent interest because of their lower toxicity, [9,13,20,21] better moisture stability, [13,22,23] isoelectronic configuration (ns 2), and comparable defect tolerance compared with Pb analogs. [24-26] For Cs 3 Sb 2 I 9 , the majority of reports have focused on studying

Large Resistive Switching and Artificial Synaptic Behaviors in Layered Cs3Sb2I9 Lead‐Free Perovskite Memory Devices

“…The layered phase, conversely, is formed at a high temperature and the dimer to layer phase formation promotes passivation of the metallic defects. [20,36] The high-resolution XPS spectrum of Sb 3d state also supports such a statement. As can be seen in Figure 2b, two strong signatures of Sb 3d states at 529.6 (3d 5/2 ) and 539.2 (3d 3/2 ) eV were present in the sample without any subsequent peak at lower binding energy corresponding to metallic antimony (Sb 0 ).…”

Synthesis of Stable Lead‐Free Cs3Sb2(BrxI1−x)9 (0 ≤ x ≤ 1) Perovskite Nanoplatelets and Their Application in CO2 Photocatalytic Reduction

“…[21] Following these seminal works, to date, high-quality lead-free Sb-based perovskites with controllable, uniform sizes and notable optoelectronic properties have been demonstrated. [22,23] These high-quality Sb-based perovskite have been successfully integrated into the wide optoelectronic field, including solar cell devices, [24,25] memristors, [26] photodetectors, [27,28] and light emitting diodes (LEDs), [29] etc. [30,31] Morphology modulation of perovskite materials is a promising strategy to further tune and enhance the materials' performance in various applications.…”

DMAI-driven all-inorganic antimony-based perovskite-inspired solar cells with record open-circuit voltage

“…19 Paul et al discovered that a small amount of Cl doping could effectively improve the film dimension and a PCE of over 2% can be achieved for PISCs with a Cs 3 Sb 2 Cl x I 9− x absorber layer. 20…”

“…19 Paul et al discovered that a small amount of Cl doping could effectively improve the lm dimension and a PCE of over 2% can be achieved for PISCs with a Cs 3 Sb 2 Cl x I 9−x absorber layer. 20 Aside from the lm dimensionality, the morphology, crystallinity, and coverage of the light-absorbing layer lm also play crucial roles in nal device performance. The solution-based spin-coating method is currently a simple and successful synthesis protocol for preparing high-quality Pb-based inorganic perovskite lms, and a mixed precursor solvent (DMF/ DMSO) was typically used to regulate the crystallization process.…”