Advancing diverse emerging solar cells with a 2D-transition metal dichalcogenide buffer

Thin-film solar cells comprising CdTe, Cu(In,Ga)Se₂ have become a less-expensive photovoltaic technology than crystalline Si wafer solar cells. Still, their efficiencies are inferior to those of their predecessors in terms of commercialization. Moreover, they consist of scarce and toxic elements.

Therefore, diverse semiconductors including Cu₂MSnS₄ (M = Co, Mn, Fe, Mg) of group I₂-II-IV-VI₄ are gaining attention due to their nontoxic nature, Earth abundance and remarkable photovoltaic properties. However, unsuitable band alignment with toxic cadmium sulfide (CdS) buffer restricts their experimental power conversion efficiencies (PCEs) to less than 5%. Exploring alternative buffers is the best path to improve their PCE.

Titanium sulfide (TiS₂) is a 2D-transition metal dichalcogenide semiconductor with excellent buffer properties. It consists of free-dangling bonds and weak van der Waals force that aid in providing proper band alignment with the absorber.

In our work published in Advanced Theory and Simulations we propose, for the first time, TiS₂ as an alternative buffer to diverse emerging Cu₂MSnS₄ (M = Co, Mn, Fe, Mg) solar cells using SCAPS-1D simulation software. Its potential and suitability were demonstrated by comparing its properties with traditional CdS.

The diverse emerging solar cells with a TiS₂ buffer displayed superior performance to CdS. They firmly surpassed CdS-based emerging solar cells by 1.36, 1.76, 1.23, and 1.15 times, accomplishing excellent PCEs of 27.02%, 27.04%, 30.04%, and 30.26% for Cu₂MSnS₄ (M = Co, Mn, Fe, Mg), respectively.

To achieve these remarkable results, we fine-tuned the buffer and absorber material parameters such as carrier concentration, thickness and defect density. These promising results set a benchmark in the field of photovoltaics.

Another important aspect is that we revealed the intrinsic characteristics of the TiS₂ buffer to compare it with CdS. The outcomes were notable—the TiS₂ buffer reduced the electron barrier at the TiS₂/Cu₂MSnS₄ (M = Co, Mn, Fe, Mg) interfaces.

In addition, lesser accumulation capacitance, significantly lower open circuit voltage losses, higher built-in potentials, and improved recombination resistance were observed in TiS₂ solar cells compared to CdS. These outstanding results revealed the immense potential of TiS₂ in enhancing the performance of diverse emerging solar cells.

In conclusion, our work extensively highlights the remarkable properties and significance of TiS₂ as an excellent alternative buffer for diverse emerging solar cells. It also delivers comprehensive guidelines for the fabrication of Cu₂MSnS₄ (M = Co, Mn, Fe, Mg) solar cells with high PCE. We strongly believe that these outcomes would benefit the burgeoning photovoltaic industry.

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Dr. Latha Marasamy is a Research Professor at the Faculty of Chemistry at UAQ, where she leads a dynamic team of international students and researchers. Her mission is to advance renewable energy, particularly in the development of second and third-generation solar cells, which include CdTe, CIGS, emerging chalcogenide perovskites, lead-free perovskites, and hybrid solar cells. She is working with a range of materials such as CdTe, CIGSe, CZTS, CdS, MOFs, graphitic carbon nitride, chalcogenide perovskites, metal oxides, MXenes, ferrites, plasmonic metal nitrides, and borides for these applications. Additionally, Dr. Marasamy is investigating the properties of novel materials and their influence on solar cell performance through DFT and SCAPS-1D simulations.