Sulfurization Growth of SnS Thin Films and Experimental Determination of Valence Band Discontinuity for SnS-Related Solar Cells

Abstract

Tin sulphide is considered to be a potential candidate for the development of low cost polycrystalline thin film solar cells. The advantages of using sulfurization process to grow SnS films were demonstrated. Polycrystalline p-type SnS films were obtained by a simple dry process at 300 °C for 90 min. The sulfurization condition depends on the deposition method of the Sn precursor. Using single-phase SnS films, band discontinuities at SnS/CdS and SnO2/SnS heterointerfaces were measured by X-ray photoelectron spectroscopy. The valence band offsets were determined to be approximately 1.5 eV for SnS/CdS and 3.5 eV for SnO2/SnS interfaces. Using these values and the energy band gaps of the corresponding layers, the energy band diagram was developed. It indicated that the SnS/CdS heterojunction is of TYPE-II form of heterostructure. This result indicated that SnS-related solar cells with CdS as window layer do not have an ideal band structure that could give high conversion efficiency.

Earth‐Abundant Tin Sulfide‐Based Photocathodes for Solar Hydrogen Production

“…The enhanced photocurrents with the introduction of n ‐CdS can be understood qualitatively with the aid of the schematic band diagram shown in Figure d. Previous reported experimental and theoretical calculations indicate that a staggered type II heterojunction is formed between the p ‐SnS and n ‐CdS . Staggered type II heterojunction implies an unrestricted flow of electrons from p‐type light‐absorber unit to the n‐type buffer layer due to appropriate interfacial energetics.…”

Band-structure, optical properties, and defect physics of the photovoltaic semiconductor SnS

“…However, SnS-based heterojunction solar cells have so far achieved rather low efficiency of below 2%, 10 which could be due to an intrinsic material limitation or due to the lack or proper device optimization, e.g., the band alignement at the heterojunction between SnS and the buffer/contact. 19 In this letter, we studied the basic PV relevant properties of SnS both theoretically and experimentally, so as to assess its potential for future PV thin-film technologies. Our band structure calculation predicts that SnS has an indirect band gap of 1.07 eV and an effective absorp-tion threshold for a SnS thin film at 1.4-1.5 eV.…”

“…According to our GW calculation, SnS has an indirect band gap of 1.07 eV, in agreement with early characteriza-tions, 18 but contrasting common perceptions that SnS is a direct gap semiconductor. 10,16,19 Fig. 1 shows the band structure along different high symmetry directions.…”

Fabrication of SnS quantum dots for solar-cell applications: Issues of capping and doping

“…SnS preferentially crystallizes in the orthorhombic herzenbergite structure. Orthorhombic SnS is amphoteric in nature (like CdTe and CIGS), has a near‐optimum direct energy bandgap around 1.35 eV, a high hole mobility (∼90 cm 2 V −1 s −1 reported), it is nontoxic, relatively inert to ambient and has an absorption coefficient of >10 4 cm −1 , however, an indirect bandgap at 1.07 eV has also been reported . Simulation studies confirm that this material has an indirect bandgap E = 1.11 eV and a direct gap of E = 1.39 eV .…”