Optimization of the window layer in large area silicon heterojunction solar cells

Abstract

Silicon heterojunction solar cells have shown great advantage due to their large open-circuit voltage which induces a high energy conversion efficiency. However, the short-circuit current density is limited by the high light absorption of an n-type amorphous silicon window layer in the short-wavelength range. Here an amorphous silicon oxide film was introduced to replace the window layer. The increasing oxygen content in amorphous silicon oxide layers leads to the enlarged optical band gap and the enhanced short-wavelength transmittance. As a result, the short-circuit current density increases obviously which comes from the high transmittance of amorphous silicon oxide films due to the wider band gap. Furthermore, the highly phosphorous-doped amorphous silicon layer was introduced to improve the contact between transparent conductive oxide layer and n-type amorphous silicon oxide layer. The carrier transport property is enhanced and thus the fill factor increases significantly. Finally, a silicon heterojunction solar cell with an area of 238.95 cm2 was prepared, yielding a total-area efficiency up to 21.1%. Overall, the results indicate that amorphous silicon oxide films can be applied to silicon heterojunction solar cells as a window layer, which provides a new route to obtain higher energy conversion efficiency.