Novel photoelectric material of perovskite-like (CH3)3SPbI3 nanorod arrays with high stability
Graphical abstract
The one-dimensional organometallic halide perovskite-like materials based on sulfur substituted amine cation exhibit high stability and optoelectronic property.
Introduction
Organometallic halide perovskite materials have been distinguished in various optoelectronic fields, such as solar cells [1], [2], optical detectors [3], light-emitting diodes [4], and laser [5]. These materials possess excellent optoelectronic properties of suitable direct bandgap, broad absorption range, bipolar charge mobility and long carrier diffusion length [6], [7]. Commonly, the organometallic halide perovskite materials are constituted with stoichiometric formula ABX3 (A = organic cation: CH3NH3+ (methylammonium, MA) [8], or CH3(NH2)2+ (formamidinium, FA [9]) B = metal ion: Pb2+, Sn2+; X = halide ion: Cl−, Br− or I−). The MA is the most popular cation in organometallic halide perovskite materials. However, the further development of MAPbI3 faces the serious challenge of rapid decomposition against moisture and heat. Under humidity, the MA cation in MAPbI3 can form weak hydrogen bonds with H2O, introducing the H2O into the crystal structure to degrade [10]. Therefore, a lot of efforts have been taken to develop the substitutions of MA that would improve the stability with high performance.
The substitution of the organic cation in MAPbI3 perovskite will change its lattice parameters, tuning the band structures [11]. Taking an example of adopting slightly larger FA to substitute MA, FA interaction with surrounding [PbI6]4− octahedral was stronger than that of MA, due to the increased hydrogen bonding [11]. The perovskite stability was enhanced because the protons from FA with stronger interaction than those from MA [12]. However, the black perovskite phase of FAPbI3 is easy to transform to the yellow perovskite phase and further degrades when exposed in humidity atmosphere, where FA cation is dissociated to ammonia and symtriazine [13]. Therefore, larger organic cations are explored to expand the perovskite system to improve stability.
Previous studies have shown that the introduction of large cations could enhance the stability of perovskite films, such as azetidinium [14], hydrazinium [15], ethylammonium [16], dimethylammonium [17], and trimethylammonium cations [17], [18]. Meanwhile, if the organic cations are too large, the perovskite films tend to form low-dimensional structure with high stability. Two-dimensional layered perovskite films with high moisture stability can be fabricated by mixing MA with equimolar phenethylammonium (PEA) [19]. Two-dimensional (Gua2PbI4) [20] and one-dimensional (GuaPbI3) [21] perovskite films were obtained using guanidinium cation. However, the issue of instability cannot be thoroughly addressed due to the amine components in the above perovskite films, because N−H bonds in amine are easy to be hydrolyzed with moisture in the air.
Sulfur-based organic cation could be stable against humidity, which should receive special attention [22]. Here, sulfur-based perovskite-like (CH3)3SPbI3 nanorod arrays were fabricated by a low-temperature solution process in air. The crystal structure of (CH3)3SPbI3 nanorod arrays is indexed to hexagonal with high purity, which shows high stability in the ambient atmosphere. After 60 days in air, the (CH3)3SPbI3 nanorod arrays have no changes in the morphology and crystal structure. Meanwhile, the (CH3)3SPbI3 nanorod arrays indicate good optoelectronic properties with a calculated energy bandgap of 2.32 eV. Further, the solar cells with the configuration of FTO/compact-TiO2/mesoporous-TiO2/(CH3)3SPbI3/VOx/Ag were fabricated, which achieved power conversion efficiency (PCE) of 2.07% with negligible hysteresis. And the (CH3)3SPbI3 nanorod arrays were also assembled as photodetector (PD) with interdigitated gold electrodes. This work proved that sulfur-based organic cation was suitable to form stable perovskite-like materials with preeminent optical and electrical properties, which would be further applied in stable perovskite optoelectronic devices for practical applications.
Section snippets
Preparation of (CH3)3SI
The (CH3)3SI powder was synthesized similarly with MAI according to our previous work [23]. Typically, 14.19 g CH3I (99.5%) was mixed with 6.21 g (CH3)2S (99.0%) under stirring at room temperature in air. The white precipitate of (CH3)3SI was formed as the following chemical Eq. (1):CH3I + (CH3)2S = (CH3)3SI
After being washed twice with diethyl ether, the white powder of (CH3)3SI was dried at 35 °C and kept in a brown bottle for further use.
Preparation of (CH3)3SPbI3 single crystal
The (CH3)3SPbI3 single crystal was synthesized by a
Results and discussion
The (CH3)3SPbI3 nanorod arrays were fabricated by a two-step solution process. Firstly, the PbI2 films were spin-coated on the substrates, reacting with (CH3)3SI solution to form (CH3)3SPbI3 nanorod arrays. To choose the suitable solvent for (CH3)3SI solution, we have investigated 20 kinds of conventional solvents as shown in Fig. S1. Among them, acetonitrile (ACN), methanol, γ-butyrolactone, water, ethylene glycol, DMF and DMSO are the excellent solvents for (CH3)3SI solution. However, only
Conclusions
In summary, we have successfully developed stable perovskite-like (CH3)3SPbI3 nanorod arrays for optoelectronic applications. The (CH3)3SPbI3 phase has a one-dimensional electronic structure and the material tends to grow along the c direction with hexagonal diameter. The carrier can effectively transfer along the direct c direction. Importantly, the (CH3)3SPbI3 nanorod arrays can stay the morphology and crystal structure in ambient air for over 60 days. The UV–vis absorption range is from 350
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
We acknowledge the financial support from the National Natural Science Foundation of China (U1732126, 11804166, 51602161, 51372119), the Natural Science Foundation of Jiangsu Province (BK20150860), the Postgraduate Research &Practice Innovation Program of Jiangsu Province (KYCX18_0846, KYCX18_0869)
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2021, Materials Today EnergyCitation Excerpt :In addition, the O 1s spectrum in Fig. 3d exhibits the characteristic SO peak at 533.60 eV [52], and the Pb 4f spectrum in Fig. 3e displays the spin-orbit doublet peaks at 139.60 and 144.55 eV, which can be ascribed to the Pb 4f7/2 and Pb 4f5/2, respectively [39]. Similarly, the I 3d spectrum in Fig. 3f exhibits spin-orbit doublet peaks for I 3d5/2 and I 3d3/2 at 620.30 and 631.85 eV, respectively [39]. These results indicate that the two-step method is suitable for the formation of TMSOPbI3 without the decomposition and oxidation of TMSOI.
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These authors contributed equally to this work.