Exceeding 30 % efficiency for an environment-friendly tandem solar cell based on earth-abundant Se/CZTS materials

• Published in: Physica. E, Low-dimensional systems & nanostructures Low-dimensional systems & nanostructures, 2019-05, Vol.109, p.52-58
• Main Authors: Ferhati, H., Djeffal, F.
• Format: Article
• Language: English
• Subjects: CZTSSe; Graded band-gap; PSO; Recombination; Selenium; Tandem; Ultra-thin layers
• ISSN: 1386-9477; 1873-1759
• DOI: 10.1016/j.physe.2019.01.002

In this paper, a new Se/CZTSSe tandem solar cell architecture is proposed as a viable approach to reach ultrahigh efficiency values at low fabrication cost. The proposed tandem design consists of a Se-based top cell with Ti intermediate ultra-thin metallic layers (MLs) and a CZTS bottom cell with graded band-gap aspect. The role of the introduced design amendments in achieving the dual-benefit of enhanced optical behavior and reduced recombination losses is investigated by means of an accurate numerical modeling. Moreover, a comprehensive study which involves the impact of design parameters such as the MLs position and the CZTSSe band-gap profile on the device performance is carried out. Moreover, Particle Swarm Optimization (PSO)-based metaheuristic technique is used to boost up the Se/CZTSSe tandem cell efficiency by identifying both the suitable position of the introduced ultrathin MLs and the appropriate CZTSSe band-gap profile. It is found that the adopted optimization approach pinpoints a new path toward achieving over 30% efficiency, not only it provides the possibility to reduce interface recombination effects by optimizing the band offset at the buffer/absorber interfaces but also enables selecting the most favorable design configuration associated with enhanced optical behavior. This makes the optimized Se/CZTSSe tandem solar cell potential alternative for providing high-efficiency and stable tandem solar cell. •A new Se/CZTSSe tandem solar cell is proposed as a viable approach to reach ultrahigh efficiency values for reliable and low-cost applications.•The proposed tandem design consists of a Se-based top cell and a CZTS bottom cell.•The introduced graded band-gap aspect and Ti ultra-thin films have a significant impact on solar cell performances.•The ability of the optimized Se/CZTSSe tandem structure for replacing perovskite-based tandem cells is demonstrated.