# The Opto-Electronic Functional Devices Based on Three-Dimensional Lead Halide Perovskites
## 3 The LHP Based Functional Devices
### Photodetectors
#### 3.2.1 Photodetectors by Combining LHP with the 2D Materials  
The 2D materials have been frequently used in LHP hybrid photodetectors. The 2D materials such as graphene and transition metal dichalcogenides (TMDCs), although possessing superior high quantum efficiency and photoresponsivity, are inferior at absorbing sufficient light due to their ultrathin nature. LHPs, on the other hand, are materials with high absorption rate, not to mention the other advantages including the long electron-hole diffusion length and ambipolar charge transport. By combining LHP with 2D materials, such as graphene and TMDCs, high-level performance could be achieved. Graphene is a zero-bandgap material and exhibits a broadband absorption. However, the ultra-thin nature as well as its fast recombination rate hinder its practical usage [103]. [PERSON] et al. have proposed a hybrid photodetector by combining MAPbI3 with graphene [94]. Efficient charge transfer from the graphene layer to LHP layer was enabled, and the hybrid device showed broad absorption band and large absorption cross-section simultaneously. Light detection in the range of 400-850 nm was achieved: at 520 nm illumination with 1 uW power, the device photoresponsivity was 180 A/W, and the detectivity was 10\({}^{9}\) Jones. The photoresponsivity was deduced to be \(\sim\)10\({}^{6}\) A/W at 1 pW, being much larger than the ZnO-based photodetectors [104]. While being in \(\sim\)uA level in graphene-only devices, the  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Materials** & **Pump (nm)** & **R(A/W)** & **D \text  
photocurrent has been enhanced to mA level in the hybrid devices, when the incident wavelength is shorter than 800 nm. To further improve the graphene/LHP device performance, people have proposed the idea of inserting gold nanoparticles (Au-NPs) [102]. Through the surface plasmonic effect of the Au-NPs, near-field of LHP could be enhanced which leads to a larger absorption cross-section and ultimately photodetection performance. The responsivity, for instance, is almost twice higher in the hybrid device with Au-NPs than the device without Au-NPs insertion. As another type of photodetection materials, TMDCs also suffer from the low-absorption efficiency. [PERSON] et al. reported a MoS\({}_{2}\)/LHP hybrid photodetectors working in 520-850 nm range [95]. The LHP layer could absorb light until 800 nm, beyond which the light is only absorbed by the MoS\({}_{2}\) layer. It is found that by using the LHP layer as the main absorber, the photoresponsivity could be enhanced by more than 7 times (from 636 to 4.9 \(\times\) 10\({}^{3}\)A/W) and the detectivity by more than 5.7 times (from 1.53 \(\times\) 10\({}^{9}\) to 8.76 \(\times\)10\({}^{9}\) [PERSON]), respectively, when compared to the MoS\({}_{2}\)-only device under 520 nm laser illumination. The enhancement disappeared at 850 nm, at which the LHP is unable to absorb the incident light. CsPbBr\({}_{3}\) nanosheets has also been used with MoS\({}_{2}\) to form heterostructure. The utilization of CsPbBr\({}_{3}\) nanosheets instead of the organic LHP counterpart could possibly increase the device lifespan but also result in the limitation of working band range due to the much larger bandgap in CsPbBr\({}_{3}\)[19]. However, since the high responsivities and gains are dependent on long carrier lifetimes, it is hard to demand a rapid response in these devices. In order to achieve both high responsivity and response speed, [PERSON] et al. proposed a Schottky barrier controlled black phosphorus (BP)/LHP phototransistor [20]. Thanks to the high electric field near the Schottky barrier, the photo-generated carriers could be rapidly extracted which led to fast response speed. The device demonstrated a high responsivity up to 10\({}^{8}\) A/W and a detectivity up to 9 \(\times\) 10\({}^{13}\) Jones, with a short response time of \(\sim\)10 ms.