Journal for Foundations and Applications of Physics
Abstract
An Ab-initio calculation in the framework of Density Functional Theory (DFT), as implemented in the FHI-aims package within Generalized Gradient Approximation (GGA) with the pbe parameterization was carried out in this work. Although methyl ammonium lead iodide (CH3NH3PbI3) has proven to be an effective photovoltaic material, there remains a main concern about the toxicity of lead. An investigation into the possible replacement of CH3NH3PbI3 with CH3NH3GeI3 and CH3NH3GeBr3 as the active layer in perovskite solar cell was carried out. The electronic band structure, band gap energy and dielectric constants were calculated for CH3NH3GeI3 and CH3NH3GeBr3. The effect of temperature on linear thermal expansion coefficient and temperature dependence of lattice constant were studied in the temperature range of 273 to 318 K. Band gap shift due to lattice expansion was also studied. The dielectric constants of these materials were also determined. The energy band gap calculated for CH3NH3GeI3 and CH3NH3GeBr3 at their respective equilibrium lattice constant are 1.606 and 1.925eV respectively. A numerical simulation with some of these materials as the active layer in a perovskite solar cell was performed using General-purpose Photovoltaic Device Model (GPVDM) and the conversion efficiency of the resulting solar cell was obtained. Conversion efficiency of 10% and 8.4% were obtained for CH3NH3GeI3 and CH3NH3GeBr3 respectively
