# The Opto-Electronic Functional Devices Based on Three-Dimensional Lead Halide Perovskites
## 3 The LHP Based Functional Devices
#### Lasers
As a trade-off, however, the device exhibited a higher lasing threshold and an increased instability as compared to the spin-coated devices, which was attributed to the remaining roughness in the LHP film [89] and remaining precursor PbI\({}_{2}\) in the film [90]. LHP-based laser threshold has been found to be reduced when the pump pulse duration was shortened [74]: for instance, the lasing threshold has been found to be 110 uJ/cm\({}^{2}\) when the pulse duration is 0.9 ns, which goes to 4 uJ/cm\({}^{2}\) when the duration is reduced to 200 fs. This reduction was finally attributed to the fact that the pump duration (200 fs) is shorter than the electron-hole recombination lifetime in LHP. The threshold could also be lower with a decreasing in defect density and scattering inside the LHP, which could be possibly achieved when the single-crystal LHP is used instead of the polycrystalline counterparts [75]. A careful design and optimization of the device configuration provides another route for performance improvement. [PERSON] et al. proposed an idea of constructing the vertical cavity structure using a cholesteric liquid crystal (CLC) as the reflector [78]. The CLC could redirect the emission that propagates along the out-of-plane and oblique paths back into the bulk to increase the optical length, thus resulting in a lower lasing threshold. The device without CLC would exhibit a broad photoluminescence (PL) even at high excitation fluence of 600 uJ/cm\({}^{2}\); in contrast, the device with the CLC showed the transformation from PL to ASE at a low threshold of 15.3 uJ/cm\({}^{2}\). Enhancement in optical confinement is another factor leads to performance improvement. [PERSON] et al. have deliberately inserted a layer of micropatterned Boron nitride (BN) between LHP microplatelet and the substrate in the WGM laser [86]. The introduction of BN could provide an epitaxial intermediary between the LHP and the substrate and also enable a better optical confinement in lasing due to the large bandgap in BN. In addition, metals have also been introduced to excite plasmonic effects to improve device performances. By hybridization of surface plasmon polaritons with the gain medium, the breaking-down of diffraction limit could be achieved. [PERSON] et al. put forward a plasmonic LHP laser by placing a MAPbI\({}_{3}\) single crystal nanowire onto a sliver substrate [83]. This plasmonic laser enables optical modes of free diffraction limit on a nanometer scale. Pumped by a 400 nm laser with a pulse duration of 120 fs, the laser demonstrated a relatively low threshold of 13.5 uJ/cm\({}^{2}\) and notably a good temperature tolerance up to 43.6 \({}^{\circ}\)C. [PERSON] et al. has developed a way to deposit an uniform aluminum nanoparticles onto the CsPbBr\({}_{3}\) microrods [84], with a lithography-free fabrication technique to avoid further damage to the LHP layer. Through optimization of deposition time, the plasmonic resonances of the aluminum nanoparticles array could be tuned to cover the emission wavelength range of CsPbBr\({}_{3}\) and modify the surface density of states on it. As a result, the laser threshold was reduced by more than 20%, and the output intensities are enhanced by more than an order of magnitude. In addition to working performance, the device stability is also a big concern to researchers. A LHP with a higher stability could be used instead of the less-stable LHP to improve the device stability: for instance, a LHP VCSEL based on CsPbBr\({}_{3}\) quantum dot (QD) or nanocrystals has been proposed, intended to achieve longer lifespan since CsPbBr\({}_{3}\) QD is more stable than MAPbI\({}_{3}\)[5, 79]. Working conditions, such as pulse duration, have