Enhanced Amplified Spontaneous Emission from All-Inorganic Perovskite Thin Films by Composition Engineering

All-inorganic CsPbBr₃ perovskite thin films are regarded as promising gain media to realize electrically pumped green laser diodes due to their good stability. However, the amplified spontaneous emission (ASE) of CsPbBr₃ perovskite thin films suffers from a relatively high threshold due to their high defect density and large scattering loss. This work demonstrates high-quality CsPbBr₃/CsPb₂Br₅ and CsPbBr₃/Cs₄PbBr₆ thin films using a vapor deposition method. Through rational design and modification on the compositions of thin films, it is found that the existence of CsPb₂Br₅ or Cs₄PbBr₆ phase in CsPbBr₃ can dramatically improve photoluminescence and lengthen carrier lifetime. The mixed phase films show good crystalline quality with lower trap density and enhanced spatial confinement. As a result, the ASE threshold of CsPbBr₃ perovskite thin film is reduced from 12.0 ± 0.2 to 10.1 ± 0.3 µJ cm⁻² (with CsPb₂Br₅) and 10.2 ± 0.2 µJ cm⁻² (with Cs₄PbBr₆). Furthermore, the optical gain is increased from 10.4 ± 0.5 to 21.6 ± 0.9 cm⁻¹ (19.5 ± 0.8 cm⁻¹) with the participation of CsPb₂Br₅ (Cs₄PbBr₆) phase. The findings provide an effective approach to lower the threshold of CsPbBr₃ lasers and shed light on the potential of stable electrically pumped perovskite lasers.