Thermodynamic Approach to Develop Lead-Free Halide Perovskites: Theoretical Study

Abstract

Metal halide perovskites (MHPs) are one of the promising candidates for next-generation photovoltaic materials. Since the Miyasa group first adopt methylammonium lead tri-iodides as a sensitizer of dye-sensitized solar cells, the efficiency of MHP solar cells has improved at an unprecedented speed. According to the recent report of national renewable energy laboratory, the certified power conversion efficiency (PCE) of MHP solar cells exceeded 23%. However, stability and toxicity are primary concerns for MHP solar cell commercialization. Among various efforts to develop Pb-free perovskite solar cells, Sn-based materials have shown the PCE. However, the stability of Sn-based perovskites is worse than Pb-based solar cells, and the multivalent features of Sn are considered to be the origin of the unstable performance. Compositional engineering and additive control can be the effective ways to develop highly stable and efficient Pb-free perovskite solar cells. This study presents the effects of compositional engineering and various additives on the stabilization of Pb-free MHP materials via ab initio thermodynamics calculations. The concept of the ‘anti-stabilizer’ for the proper selection of the preferred phase is suggested by our previous report[1]. We present that the anti-stabilizing concept can be successfully applied to stabilize the proper band gap polymorph of black CsSnI3[2]and Bi-based layered perovskites. Additionally, the roles of additives including small alkali metal interstitials are discussed concerning thermodynamics. [1] J. Jeon, T. Eom, E. Lee, S. Kim, S. Kim, K.-H. Hong, H. Kim, J. Phys. Chem. C 121 (2017) 9508–9515. [2] J.H. Heo, J. Kim, H. Kim, S.H. Moon, S.H. Im, K.-H. Hong, J. Phys. Chem. Lett. 9 (2018) 6024–6031.