Negative electron affinity driven broadband absorption of Cs3+nPbnSb2I9+3n/GaN van der Waals heterostructures

Metal halide perovskites (MHPs) with highly sensitive photoelectric response and ultrahigh absorption coefficient in the visible range exhibit huge potential as building blocks for optoelectronic devices. However, these perovskites suffer from poor absorption efficiency in the infrared range due to the weak coupling of infrared light. In this work, we report a new class of MHP-based heterostructures by the integration of two-dimensional Cs3+nPbnSb2I9+3n perovskites with GaN nanosheets for the realization of highly efficient carrier separation and broadband absorption. We find that the formation of the Cs/GaN(0001) interface in Cs3+nPbnSb2I9+3n/GaN heterostructures can induce the shift of the vacuum level below the conduction band minimum, resulting in negative electron affinity (NEA). Moreover, the NEA of the heterostructures is not sensitive to the thickness of perovskite and GaN layers. Owing to the type-II band alignment and NEA of these heterostructures, they exhibit highly efficient carrier separation and enhanced optical absorption from the infrared to ultraviolet light region, which result in maximum power conversion efficiency as high as 28.5%. The findings suggest the large potential of Cs3+nPbnSb2I9+3n/GaN heterostructures for optoelectronic applications, such as solar cells, photodetectors, and field emission device.