Structural, Optical And Electronic Properties Of Organometal Halide Perovskites For Photovoltaic Applications

Résumé: Organometallic perovskites (OMHP) based solar cells; with higher than 25% of power conversion efficiency (PCE), attract special attention. Using calculations, the first task confirms earlier experimental findings and determines optimal properties for the studied (MAPbX3) (X=I,Br,Cl) family. Values of energy band gap, density of states, absorption coefficient α, refractive index n, dielectric constant ε and elastic constants cij of orthorhombic methylamunium lead halides (MAPbX3) (X=I,Br,Cl) are all calculated using Density Functional Theory (DFT) method with generalized gradient approximation (GGA). The stiffness of (MAPbX3) (X=I,Br,Cl) is investigated by calculating Young ’s moduli E constants. Among the series, MAPbI3 is the stiffest material with Ex=57.2 GPa. These perovskites are characterized by their tuned energy band gap: Eg MAPbI3, MAPbBr3, MAPbCl3=1.626, 2.207 and 2.748 eV, respectively. They also exhibit a remarkable absorption coefficient (α MAPbX3=105 cm−1) over a wide energy range, particularly in the visible spectrum [1.65–3.26 eV]. The anisotropy of optical properties (MAPbX3) (X=I,Br) is proven in the near and middle ultraviolet [3.1–5 eV] energy band. In the second task, the effect of Ag and Cd atoms substitution on MAPbI3 structural and optoelectronic properties is studied, based on the ab-initio DFT method. Properties of MAPbI3 and MAABxPb1-xI3(Bx=Ag0.17 or Cd0.5) perovskites, in their orthorhombic phase, are described. The energy band gaps are calculated here with PBE-GGA and HSE06 methods. The MAPbI3 is characterized by its high absorption coefficient over the visible spectrum [1.65–3.26 eV] compared to MAAg0.17 Pb0.83 I3 (α=104–0.6×105cm−1), and MACd0.5 Pb0.5I3 (α=1.5×104–0.4×105cm−1). Low anisotropic electron and hole effective masses are found for all compounds in the range of 0.043 m0-0.188 m0. The anisotropy in optical properties for MACd0.5 Pb0.5I3, such as the α, ε and n, is noticed. Enhancement in refractive index n of MAAg0.17 Pb0.83I3 is also observed. The calculated values for n are 2.90, 2.75 and 2.00 for MAAg0.17 Pb0.83I3, MAPbI3 and MACd0.5Pb0.5I3, respectively, at 2.5 eV energy peak value. The values for κ are 1.4, 1.8, and 1.2 for MAAg0.17 Pb0.83I3, MAPbI3 and MACd0.5Pb0.5I3, respectively, at 3.5 eV energy peak value.

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