Protection-Free Ag Nanowires as a Transparent Conductive Electrode for Improved Cu(In1-x, Gax)Se2 (CIGS)-Based Photovoltaic Performances

A rather low efficiency for Cu(In1-x, Ga-x)Se-2 (CIGS)-based solar cells (mostly less than 1%) is generally reported, where silver nanowires (Ag NWs) are employed as a top transparent conductive electrode (TCE). The weak adhesion and small contact area between the Ag NWs and the n-type buffer layer remain an acknowledged issue to be addressed. Here, a modified polyol reduction process was elaborately proposed, on the basis of the regulation of the PVP molecule's steric effect and cationic chemical characteristics. Ag NWs with controllable lengths and diameters were successfully synthesized, to meet the optimization of the photovoltaic performance. The mixed PVP consisting of short and long chains works very effectively, in increasing the length and shortening the diameter. We attribute this to the large steric hindrance-induced protective shielding on {100} planes by insertion of the short chains into the long ones. Cationic chemical characteristics, on the effect of Ag morphological evolution, were also referred and carefully conducted. Importantly, a champion efficiency of 4.97% on pristine Ag NWs without protection and post-treatment as a TCE was achieved, and this was attributed to the enhanced adhesion and increased contact area between Ag NWs and the top of buffer layer.