Optimization of Front TCO Layer of Silicon Heterojunction Solar Cells for Tandem Applications

The front transparent conductive oxide (TCO) layers of silicon heterojunction solar cells need to be optimized electrically and optically to minimize losses due to sheet resistance and free carrier absorption. This optimization has already investigated for the wavelength range of 300-1100 nm, but not for the projected wavelength range of 700-1100 nm for a silicon cell that is applied in a tandem structure as the bottom cell. Here, we demonstrate a routine for determining the total loss associated with the front TCO layer and employ it to determine which carrier density, mobility, and finger pitch combinations minimize loss. For a representative ITO film with a mobility of approximately 20 cm(2)/Vs and a carrier density of approximately 2.5x10(20) cm(-3), the total loss over the wavelength range of 700-1100 nm is minimized by using a finger spacing of 3 mm and ITO thickness of 100-110 nm.