Abstract
This research starts with the computational quantum mechanics, using first principles to simulate the chlorine doping effect with different concentration (x value) on the optical and thermoelectric properties of 3D mixed halide methylammonium lead perovskites (MAPbI3-xClx). Finding the highest thermoelectric figure of merit (ZT) and suitable solar absorbance range are our major targets. The 3D bulk MAPbI3 is considered as a potential mineral semiconductor material for future solar cells and thermoelectric chips. It has good electrical properties, low thermal conductivity, and only needs low cost to produce. This research employed the Khon-Sham theory, PBE (Perdew–Burke–Ernzerhof) exchange correlation energy functional, and self-consistent field (SCF) method, to calculate the plane wave in the reciprocal space. In the electron simulation, we used the density functional theory (DFT) to evaluate the band structure and electron density of states to calculate the optical band gaps. Then applying Boltzmann transport equation (BTE) to calculate the electrical conductivity σ, carrier thermal conductivity κ_el, and Seebeck coefficient S. In the phonon simulation, we used density functional perturbation theory (DFPT) to evaluate the phonon dispersion relation and phonon density of states, and applied the Debye model to calculate the phonon thermal conductivity κ_ph. This research has found that the main contribution to the heat transfer is mainly from phonons, especially the optical parts, the contribution from electrons is little. In addition, doping Cl will increase not only electrical conductivity, but also phonon thermal conductivity. The latter is because of the production of soft modes and the reduction of averaged weight. At the very low Cl doping concentration, e.g. x=0.25, electrical conductivity increases while the thermal conductivity almost remain the same values as MAPbI3, ZT value rises up from 1.41×〖10〗^(-7) to 8.26×〖10〗^(-7). The latter is about 6 times greater than the former. Doping carriers, such as electrons or holes, ZT value can grow up to 10 times the value of MAPbI3, at the same carrier concentration condition. When electron or hole doping concentration reaches 〖10〗^20 cm^(-3), the ZT value of MAPbI3 would achieve 2.00×〖10〗^(-5) and 2.21×〖10〗^(-4) respectively, which is 1000 times the value of the intrinsic condition, and it’s 2.09×〖10〗^(-4) and 2.09×〖10〗^(-3) for condition x=0.25. In the study of the optical property, we obtained that the main absorbance wavelength located in the ultraviolet light region (40nm < λ < 400nm) and visible light region (400nm < λ < 700nm). MAPbI3-xClx has wider absorption range, but its absorption coefficient decreases with the Cl concentration. The design of the heat absorber of the solar thermoelectric chips must enhance the thermal radiation absorption in the range of λ ≥ 400 nm, which is the region from visible to infrared light. Finally, the conclusion of this research is that the MAPbI2.75Cl0.25 is the best tuning for the light absorption layer in the solar cell, and highest ZT value for the thermoelectric chip. Hence it can improve the performance of future solar thermoelectric chips.