Energy barrier at the N719-dye/CsSnI3 interface for photogenerated holes in dye-sensitized solar cells

Abstract

This report is to address the question if black γ-polymorph of cesium tin tri-iodide (B-γ-CsSnI3) can be used as a solid-state hole-transport material in the conventional DSSCs with the N719 dye to replace the liquid electrolyte as reported by I. Chung et al. on Nature 485, 486, (2012). Here we demonstrate rigorously that B-γ-CsSnI3 is not energetically possible to collect photogenerated holes because of the large energy barrier at the interface of N719/B-γ-CsSnI3. Therefore, it cannot serve as a hole-transporter for the conventional DSSCs although it is a good hole-conducting material. A solution-based method was employed to synthesize the B-γ-CsSnI3 polycrystalline thin-films used for this work. These thin-films were then characterized by X-ray diffraction, Hall measurements, optical reflection, and photoluminescence (PL). Particularly, spatially resolved PL intensity images were taken after B-γ-CsSnI3 was incorporated in the DSSC structure to insure the material integrity. The means of ultraviolet photoemission spectroscopy (UPS) was used to reveal why B-γ-CsSnI3 could not act as the substitute of liquid electrolyte in the conventional DSSCs. For the completeness, other two related compounds, one is the yellow polymorph of CsSnI3 and other is Cs2SnI6 with tetravalent tin instead of double-valent tin in CsSnI3 were also investigated by UPS.

Intrinsic defects in a photovoltaic perovskite variant Cs2SnI6

“…2b) and n is ~10 . These theoretical results seem to explain the experimental results reported to date; i.e., the electrical properties of Cs2SnI6 ranging from insulating 18 to low-density n-type conduction (n ~110 14 cm…”

“…On the other hand, Cs2SnI6 have not shown p-type conductivity unlike the other Sn 2+ -based compounds and have shown ntype conduction or insulating behavior depending on the synthetic routes. Lee et al 13 reported the native n-type conduction with electron density (n) of ~110 14 cm 3 in polycrystalline Cs2SnI6 pellets annealed at 200 o C, while Zhang et al 18 observed very high resistivity in room temperature-processed Cs2SnI6. Therefore, in order to clarify the intrinsic nature of Cs2SnI6 and its origin, a systematic theoretical study on the intrinsic defects is important, which will provide a guiding principle for tuning its properties for photovoltaic and other semiconductor applications.…”

Influence of Rb/Cs Cation-Exchange on Inorganic Sn Halide Perovskites: From Chemical Structure to Physical Properties

“…For this work, to reflect the general synthesis reaction of halide perovskites (i.e., AX + BX 2 → ABX 3 ), 17,21,22 here we simply use i as the bulk components CsI, RbI, and SnI 2 , respectively, rather than atomic species Cs, Rb, Sn, and I.…”

Lead‐Free Metal Halide Perovskite Nanocrystals: Challenges, Applications, and Future Aspects

“…One of the promising alternatives of Pb (II) is Sn (II), which has been demonstrated in bulk and thin films for solar cell applications ,. The single crystals of MASnI 3 and FASnI 3 are found to be p‐type and n‐type semiconductors respectively with the trap densities in the order of 10 11 cm −3 .…”