Impact of KF-post deposition treatment on Cu(In,Ga)Se2 surface and Cu(In, Ga)Se2/CdS interface sulfurization

Partial sulfurization of Cu(In,Ga)Se-2 (CIGSe) absorbers contributes to enhance photovoltaic performance of chalcopyrite based solar cells. Alternatively, KF post-deposition treatment (KF-PDT) performed under Se atmosphere has recently been used to improve the efficiency of CIGSe thin film based solar cells. In this work, we study the potential sulfurization of KF-treated CIGSe during the chemical bath deposition of the CdS buffer layer. Therefore, buried interfaces between KF-PDT CIGSe under Se or S atmosphere and CdS are investigated with the help of non-destructive and depth sensitive X-ray emission spectroscopy. No CIGSe sulfurization is detected at the absorber/CdS interface when KF treatment is performed under selenium atmosphere. In contrast, when KF treatment is done under sulfur atmosphere, partial sulfurization of CIGSe is detected at the CIGSe/CdS interface. We show through X-ray photoemission spectroscopy that the CIGSe sulfurization occurs during the KF-PDT performed under sulfur atmosphere. We also demonstrate that alkali favors greatly CIGSe surface sulfurization when the chalchopyrite is exposed to sulfur atmosphere.