# The Opto-Electronic Functional Devices Based on Three-Dimensional Lead Halide Perovskites
## 2 The Properties of the LHP Materials
### Optical and Electrical Properties of LHP  
The LHPs are considered as outstanding candidates for next-generation opto-electronic applications, mostly due to the fact that the materials demonstrate outstanding optical and electrical properties in various aspects, as shown in Figure 2. The LHPs are direct band-gap semiconductors, and the band-gap could be conveniently tuned by chemical composition (for instance, changing the halogen elements) and thus enabled to cover a wavelength range from visible to near-infrared [28,29]. The LHPs have large absorption coefficients. Taking CH\({}_{3}\)NH\({}_{3}\)PbI\({}_{3}\) (MAPbI\({}_{3}\)) as an example, its absorption coefficient is found to be in the level of \(\sim\)10\({}^{5}\) cm\({}^{-1}\) in the visible range, being much larger than GaAs [30]. A large absorption coefficient, as well as a widely tunable bandgap, will contribute to a high-performance in photodetectors. LHPs also have high luminescence quantum yields. For solution-processed MAPbI\({}_{3}\)-Cl\({}_{3}\) crystalline films as an example, a high photoluminescence (PL) quantum efficiency up to 70% has been reported [31]. MAPbI\({}_{3}\) films have been found to demonstrate an outstanding gain of 3200 \(\pm\) 830 cm\({}^{-1}\), which is comparable to conventional light-emitting materials [32]. The high luminescence quantum yield along with the tunable band-gap, makes LHPs ideal candidates for applications including lasers and LEDs. LHPs are found to have high carrier mobility, long diffusion length, and low trap-related recombination rates [35, 36, 37]. These properties govern carriers' transport dynamics which are important in applications such as photodetection. Carrier mobility and diffusion length are closely related to each other, and these two parameters show similar dependence on factors including crystalline quality and chemical composition [35]. The crystalline quality seems to be a dominant factor, and the mobility/diffusion length is much larger for single-crystal samples than its film counterparts. For instance, the hole mobility has been found to be \(\sim\)164 cm\({}^{2}\)/(Vs) in solution-processed single-crystalline characterized using space charge limit current (SCLC) technique [38,39], which goes to \(\sim\)0.4 cm\({}^{2}\)/(Vs) in poly  
Figure 2: Optical and electrical properties of LHPs. **(a)** Representative photoluminescence (PL) spectra for CsPbX\({}_{3}\)Y\({}_{3-x}\), where X and Y represents different halide elements, demonstrating a wide wavelength tunability for LHP. Reprinted with permission from [33]. Copyright 2015 American Chemistry Society **(b)** The absorption coefficient (\(\alpha\)) of CH\({}_{3}\)NH\({}_{3}\)PbI\({}_{3}\) (MAPbI\({}_{3}\)), CsSnI\({}_{3}\) and GaAs. Reproduced with permission from [30]. ; published by Wiley, 2014. **(c)** The photoluminescence quantum efficiency (PLQE) of MAPbI\({}_{3}\)-Cl\({}_{3}\) films. The inset shows the normalized PL intensity (integrated from 1.71 to 1.57 eV) and the transient absorption (TA) signal versus time for device and film samples. Reprinted with permission from [31] Copyright 2014 American Chemistry Society. **(d)** Absorption coefficient of MAPbI\({}_{3}\) perovskite films, for which the absorption onset is at 1.55 eV. Reproduced with permission from [32]. ; published by Wiley, 2015. **(e,f)** mobility and diffusion of MAPbI\({}_{3}\). In both panels, the black dots represent experimental data, and the regions marked by different colors from left to right correspond to orthorhombic, tetragonal, and cubic phase, respectively. The dashed lines in **(e)** is T\({}^{-3/2}\) dependence prediction for band-like transport, and in **(f)** is an eye-guide. Reproduced with permission from [34]; published by Wiley, 2015.  
crystalline films [40]. The carrier diffusion length in MAPbI3 single crystals could be more than 175 \(\mu\)m [39], which could be reduced to 0.1 \(\mu\)m in MAPbI3 films [41]. Chemical composition tuning also enables the alteration of mobility and diffusion length.