Giant Nonlinear Optical Response in 2D Perovskite Heterostructures

2D layered halide perovskites have attracted significant attention. Apart from the linear optical properties, it is also intriguing to explore the nonlinear optics of 2D layered halide perovskites and their heterostructures. Previous nonlinear optical (NLO) studies of 2D perovskites primarily focus on the thin films or microplates. Herein, the NLO properties of ( n ‐C 4 H 9 NH 3 ) 2 PbI 4 /( n ‐C 4 H 9 NH 3 ) 2 (CH 3 NH 3 )Pb 2 I 7 heterostructures with centimeter size are systematically studied. The NLO properties can be continuously tuned by changing the thickness. A giant two‐photon absorption (2PA) coefficient up to 44 cm MW −1 is obtained for the heterostructures with a total thickness of 20 µm based on the nonlinear transmittance measurement. Additionally, strong multiphoton‐induced photoluminescence is observed in the heterostructures. It is proposed that the giant 2PA coefficient might arise from the small thickness (≈1 µm) of ( n ‐C 4 H 9 NH 3 ) 2 (CH 3 NH 3 )Pb 2 I 7 layer and possibly the nonradiative energy transfer between the different constituting layers within the heterostructures through an antenna‐like effect. Finally, benefiting from the giant 2PA coefficient, direct detection of 980 nm light is demonstrated with a responsivity of 10 −7 A W −1 in the heterostructures. The findings suggest the promising applications of 2D perovskite heterostructures in the infrared photodetection and some other nonlinear absorption related optoelectronic devices.