Functions of oxygen atoms in hydrogenated amorphous silicon oxide layers for rear-emitter silicon heterojunction solar cells

Reducing the parasitic absorption of intrinsic hydrogenated amorphous silicon [a-Si:H(i)] films is crucial for enhancing the short-circuit current density (Jsc) of silicon heterojunction (SHJ) solar cells. Herein, a-Si:H(i) films were replaced by intrinsic hydrogenated amorphous silicon oxide [a-SiOx:H(i)] films with wider band gap at the front of rear-emitter SHJ solar cells and the microstructure of a-SiOx:H(i) films was modified with the flow ratio of carbon dioxide to silane. A-SiOx:H(i) films showed lower absorption coefficients at short wavelengths and led to a 0.13 mA/cm2 absolute increase of Jsc. Additionally, higher open-circuit voltages (Voc) were achieved thanks to the better interface passivation and the fill factors (FF) almost kept constant due to avoiding the impediment of hole transport. However, the higher oxygen content in a-SiOx:H(i) films associated with the worse electrical performance hence carbon dioxide-to-silane flow ratio should be adjusted at a low value. Finally, a conversion efficiency (Eff) gain of 0.12%abs was obtained for the optimized SHJ solar cells as a result of the improvements of both Voc and Jsc. More importantly, a-SiOx:H(i) layer exhibited better damp-heat stability than a-Si:H(i) layer in sodium environment. This work clearly interpreted the functions of oxygen atoms in a-SiOx:H(i) films and offered a valid approach to reducing the parasitic absorption losses of SHJ solar cells.