Energy band offsets of SnS-based solar cell structure using various n-type semiconductors, such as CdS, SnS2, In2S3, ZnIn2Se4, ZnO, and Mg0.3In0.7O, are evaluated by photoelectron yield spectroscopy. The valence band discontinuities are estimated to be 1.6 eV for both SnS/CdS and SnS/SnS2, 0.9 eV for SnS/In2S3, 1.7 eV for SnS/ZnIn2Se4, and 1.8 eV for both SnS/ZnO and SnS/Mg0.3Zn0.7O. Using the valence band discontinuity values and the corresponding energy bandgaps of the layers, energy band diagrams are developed. This study implied a type-I heterostructure, appropriate for SnS-based solar cell, for the ZnIn2Se4 or MgxZn1−xO (0 ≤ x ≤ 0.3) interface and type-II for other junctions.
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.
Summary
Debutant analysis of the parameters impeding the efficiency of the CdS/SnS‐based photovoltaic device is the chief novelty of the present report. We have developed thin‐film heterojunction solar cells with the stacking sequence: glass/Al‐doped ZnO/CdS/SnS/In. The two crucial issues, band offsets and cell studies, are discussed in detail. The band offsets at the CdS/SnS interface have been systematically evaluated by semidirect X‐ray photoelectron spectroscopy. The calculated valance band offset (ΔEv) and conduction band offsets (ΔEc) are found to be 1.46 and −0.36 eV, respectively. The negative value of conduction band offset indicates that the junction formed is of type‐II (staggered‐type heterojunction). Electrical studies revealed power conversion efficiency of 0.32% with VOC, JSC, and fill factor as 170.61 mV, 7.26 mA/cm2, and 0.26, respectively. The impact of the offset values on the cell studies is clearly elucidated. The reasons for the low efficiency are spotlighted. Collectively, this article gives the overview of the systematic approach undertaken to get obvious picture about the barriers that limit the conversion efficiency of the CdS/SnS‐based solar cell and the measurements required for enhancing the efficiency of the SnS‐based solar device.
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