Engineering Energy Cascades in Quasi‐2D/3D Perovskites Toward Low‐Threshold Amplified Spontaneous Emission

Abstract Metal halide perovskites, particularly quasi‐2D perovskites, have emerged as promising candidates for next‐generation laser diode gain media due to their exceptional optoelectronic properties. However, conventional quasi‐2D perovskites suffer from inefficient exciton funneling and pronounced efficiency roll‐off at high carrier densities. Here, a quasi‐2D/3D perovskite structure is proposed with a high‐efficient energy cascade, modulated through molecular engineering strategy. The C─O─C functional groups in PEO form hydrogen bonds with PEA + , thereby delaying the assembly of PEA + with the [PbBr 6 ] 4− octahedra inorganic layer. This modification led to refined grain size, enhanced crystallinity, and improved surface flatness in the resulting films. Furthermore, the engineered quasi‐2D/3D thin film exhibits an increased exciton binding energy while alleviating efficiency roll‐off at high carrier density, achieved by effectively suppressing Auger recombination through directional energy transfer from the quasi‐2D to the 3D phase. Consequently, the amplified spontaneous emission threshold of quasi‐2D/3D films is reduced to 16.6 µJ cm −2 , and obtained a higher net modal gain coefficient (892 cm −1 ). These findings provide critical insights for developing low‐threshold perovskite lasers.