Fig. 3

Narrowband photodetection in the entire visible range. a Reflection spectra of the perovskite single-crystal plates. Red dots indicate the exciton peak, whereas blue rhombus mark the self-trapped states below the bandgap. b Normalized EQE spectra of the vertical devices (Config. 1) based on 2D perovskite of different halide compositions and layer number n. Measurements were carried out under a bias of 5 V