Experimental disclosing the composition- and structure-dependent deep-level defect in photovoltaic antimony trisulfide materials


 Antimony trisulfide (Sb2S3) represents a kind of emerging light-harvesting material with excellent stability and abundant elemental storage. Due to the low-symmetry, theoretical investigation has pointed out that there exists complicated defect properties. However, there is no experimental verification on the defect property. Here, we conduct optical deep-level transient spectroscopy to investigate defect properties in Sb2S3 and show that there are maximum three kinds of deep level defects observed, depending on the composition of Sb2S3. We also find that the Sb-interstitial (Sbi) defect does not show critical influence on the carrier lifetime, indicating the high tolerance of the one-dimensional crystal structure where the space of (Sb4S6)n ribbons is able to accommodate impurities to certain extent. This work provides basic understanding on the defect properties of quasi-one-dimensional materials and a guidance for the efficiency improvement of Sb2S3 solar cells.

Antimony trisulfide (Sb2S3) represents a kind of emerging light-harvesting material 23 with excellent stability and abundant elemental storage. Due to the low-symmetry, 24 theoretical investigation has pointed out that there exists complicated defect properties. 25 However, there is no experimental verification on the defect property. Here, we conduct  Herein, we experimentally uncover the defect characteristics by using deep level 67 transient spectroscopy (DLTS) and identify the details of the defect. We examine both 68 Sb-rich and S-rich Sb2S3 films for a comparative study which is prepared by thermal 69 evaporation approach. To make clear conclusions, we carefully analyze the crystallinity, 70 electronic structure and chemical composition (impurity) of the as-obtained films. In 71 contrast to the theoretical study where complicated defect proposed in the Sb2S3 8-11 , our 72 experimental investigation shows only a few types of defect, and the defect type and 73 concentration is sensitively dependent on anion/cation ratio.

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Structure and composition characterization of Sb2S3 films. Due to the high saturated 76 vapor pressure of sulfur, the sulfur loss is inevitable and results in Sb-rich films during 77 thermal evaporation deposition. To obtain S-rich Sb2S3 film, we apply a co-evaporation 78 3 equipment for the Sb2S3 film fabrication, in which S powders are co-evaporated with 79 Sb2S3 for the generation S-rich Sb2S3 films. The synthesis details are provided in the 80 Methods section. The as-obtained films at Sb-rich and S-rich conditions display similar 81 morphology (Fig. 2a, 2b and Supplementary Fig. 1). X-ray diffraction (XRD) is then 82 applied to characterize the crystallinity (Fig. 2c). Both of the films display diffractions  According to the energy dispersive X-ray spectroscopy (EDS), the atomic ratio of S/Sb 86 in Sb-rich and S-rich Sb2S3 films are calculated to be 1.28 to 1.55 (Supplementary Table   87 1), respectively.  CdS since its band gap is 2.4 eV. On the ground of both J-V and EQE analysis, the as-120 prepared S-rich Sb2S3 films display high photovoltaic quality.

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Bulk deep-level defects analysis. In this characterization, there is a typical concern on 122 5 traditional electric DLTS regarding the distortion of minority-carrier trap detection 18 .

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Whereas attaching optical pulse to DLTS is recognized as an effective means to improve 124 the sensitivity and authenticity of minority-carrier traps detection 19,20 . Herein, we adopt   Table 1,   139 where ET, σ, NT, τ and NS are trap energy level, capture cross section, trap density, and S-rich Sb2S3 films ( Fig. 6a and b, Supplementary Fig. 5). Strikingly, there appear   For the Sb2S3 solar cell development, one of the major concern is the efficiency from the split of quasi-Fermi level for electron and hole (Fig. 5c)  An interesting finding in this study is that the existence of Sbi in the Sb-rich Sb2S3 219 film generates less detrimental effect on the carrier lifetime, which should be related to 220 Q1D crystal structure where the space between (Sb4S6)n ribbons can afford impurities 221 to certain degree. However, the Si defect does not appear in the S-rich Sb2S3 film, it is 222 most likely that the sulfur is easy to be evaporate out during the film deposition at high 223 temperature. Finally, we find that the Sb-rich film displays two types of crucial defect, 224 i.e. VS and SbS, while S-rich Sb2S3 film shows only one kind of critical defect, VSb.

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Therefore, the S-rich Sb2S3 film seems more promising for achieving next efficiency MHz, Ti-sapphire laser) and white light generated with a sapphire plate, respectively.

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The decay characteristics were fitted by biexponential model y=ΣAiexp ( All data that support the findings of this study are available within the paper and the 280 supplementary information.