The Importance of Low Electron Affinity Materials as the n-type Layers of CIGS2 Solar Cell Design

Despite its potential in the single-junction solar cell application, extensive research into the wide bandgap CuIn
1−x
Ga
x
S
2
(CIGS
2
) solar cell material has yet to be done to date. In this work, we aimed to clarify the role and design rule of the n-type layers in determining the open-circuit voltage of the CIGS
2
solar cell through a numerical study. By using two simulation models of different device structures, we determined the maximum open-circuit voltage as a point of reference and investigated the appropriate n-type materials for a CIGS
2
solar cell device. In this work, the use of low electron affinity n-type materials has demonstrated high open-circuit voltage, even in the presence of a high interface defect concentration, in both the window/absorber and window/buffer/absorber structures. Additionally, our work also highlighted that a high performing buffer-free CIGS
2
solar cell is attainable through a specific n-type material selection for the window layer with a low electron affinity material property.