Lead-free double perovskites: how divalent cations tune the electronic structure for photovoltaic applications

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2022-09, Vol.1 (34), p.12276-12285
• Main Authors: Ibrahim, Ismail A. M, Chung, Chan-Yeup
• Format: Article
• Language: English
• Subjects: Configurations; Divalent cations; Dopants; Electronic structure; Electrons; Energy gap; Lead free; Optoelectronics; Orbitals; Perovskites; Photovoltaic cells; Solar cells; Toxicity
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc02903k

Recently, the efficiency of perovskite-based solar cells has reached 25.7%. Due to lead toxicity, lead-free double perovskites have received great attention as potential candidates for photovoltaic applications. Keeping in mind the significant challenges (indirect and wide bandgaps) related to most of the present double perovskites, we used ab initio calculations and incorporated divalent and tetravalent dopant cations at the mixed B-site of Cs 2 AgSbCl 6 to tune the electronic structure for optoelectronic applications. The doped perovskites are structurally and thermodynamically stable. The tunability of the electronic structure is shown for Sn 2+ - and Ge 2+ -doped configurations due to the strong hybridization between the dopant orbitals (s 2 p 0 ) and the host orbitals at the band edges. The predicted bandgaps of the doped perovskites are of a direct character and in the ideal range (1.70-1.90 eV) for the top cell in tandem solar cells. The inclusion of Zn 2+ , Cd 2+ , Sn 4+ , and Ge 4+ with the electronic configurations of d 10 s 0 and s 0 p 0 resulted in a negligible modification of the electronic structure, and hence did not show an indirect-direct bandgap transition. Therefore, the contribution from the dopant orbitals at the band edges dominates the electronic structure tunability of the doped perovskites. Furthermore, an enhanced absorption efficiency is observed for the Sn 2+ - and Ge 2+ -doped perovskites. This work provides a computational guide for exploring low-cost and non-toxic dopants for the electronic structure-engineering of double perovskites as photo-absorbers in future solar cell applications. The tunability of the electronic structure and the optical performance of Cs 2 AgSbCl 6 double perovskite for photovoltaic applications is shown via Sn 2+ and Ge 2+ doping as a consequence of the dopant orbital contribution at the band edges.