Efficiency Improvement by Optimization of Absorber Layer and n-Layer in a-Si: H/a-SiGe:H Advanced Thin Film Solar Cells

In this paper the effect of the absorber layer and n-layer properties such as thickness and doping concentration on the electrical characteristic of the a-Si:H/a-SiGe:H thin film hetero structure solar cells such as photo-generation rate, recombination rate and electric field through the cell is investigated. Introducing Ge atoms to the Si lattice in Si-based solar cells is an effective approach in improving their characteristics. Especially, current density of the cell can be enhanced without deteriorating its open circuit voltage. Optimization shows that for an appropriate Ge concentration, the efficiency of a-Si: H/a-SiGe solar cell is improved by about 6.5% compared with the traditional a-Si: H solar cell. This work presents a novel numerical evaluation and optimization of amorphous silicon double junction (a-Si:H/a-SiGe:H) thin film solar cells and focuses on optimization of a-SiGe:H mid-gap single junction solar cell based on the optimization of the Ge content in the film, thick nesses of the i-layer and n-layer, and doping concentration of the films. Maximum efficiency of 23.5%, with short circuit current density of 265 A/m² and open circuit voltage of 1.13V for double junction solar cell has been achieved.