Modify the Schottky contact between fluorine-doped tin oxide front electrode and p-a-SiC:H by carbon dioxide plasma treatment

•CO2 plasma treatment is a simple and effective way to modify the interface of p-a-SiC:H/FTO.•The behavior of the radicals in COP and the mechanism of the COP treatment on FTO was proposed.•Both of the Voc and FF of the a-Si:H solar cells have been improved based on the COP treatment.

Carbon dioxide plasma (COP) treatment of a fluorine-doped tin oxide (SnO2:F, FTO) front electrode was used for the fabrication of p–i–n hydrogenated amorphous silicon (a-Si:H) solar cells. The oxygen and carbon monoxide radicals in COP play important roles of de-doping and doping effects on the surface of FTO, respectively. Through changing the COP treatment time, the de-doping and doping effects could alter the number of oxygen vacancies for both the bulk and the surface of FTO, resulting in an increase in the work function (WF) and a decrease in the Schottky barrier at the p-a-SiC:H/FTO interface. Due to an increase in the WF from 4.16 eV to 4.34 eV after 95 s treatment, the open circuit voltage (Voc) of the a-Si:H solar cells increased from 915 mV to 965 mV and the fill factor (FF) increased from 67.7% to 74.4%. Although the short-circuit current density (Jsc) decreased from 11.76 mA/cm2 to 10.36 mA/cm2 after 95 s COP treatment due to the weakness of Burstein–Moss (BM) shift and the recombination at FTO surface, the conversion efficiency of the a-Si:H solar cell was enhanced by 12.24% after 45 s COP treatment, accompanied by improving the Voc and FF with almost constant Jsc.