Strain relaxation and domain enlargement via phase transition towards efficient CsPbI2Br solar cells

Abstract

CsPbI₂Br perovskite is emerging as an attractive photovoltaic material due to its excellent stability against heat and illumination. However, a huge tensile stress of about 162 MPa is created during the CsPbI₂Br film formation, resulting in a high defect density, severe non-radiation recombination loss and instability of CsPbI₂Br PSCs. Herein, an α → δ → α phase transition growth (PTG) approach is developed for the deposition of CsPbI₂Br films that allows relaxation of the relative tensile strain by 62 ± 4% and increases the domain size by 800%. The CsPbI₂Br films realize a low defect density of 5.59 × 10¹⁵ cm⁻³ and a reduced Urbach energy. PSCs prepared by the PTG approach achieve a PCE of 16.5% with a remarkably high V_oc of 1.36 V. These CsPbI₂Br PSCs retain 90% of their initial efficiency after storage under 10–15% relative humidity (RH) conditions for 1200 h and 90% of their initial efficiency after heating at 65 °C for 800 h.