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We report on the fabrication of a robust and flexible transparent electrode to replace costly and fragile indium tin oxide (ITO) used in flexible Cu(In,Ga)Se2 solar cells, composed of an aluminum doped zinc oxide (AZO)/Ag-nanowires/aluminum doped zinc oxide (AZO) (AAA herein) sandwich structure. The Ag-NWs networks form low-resistance, long-range pathways throughout the electrode that are able to maintain efficient charge carrier collection and extraction after strenuous mechanical bending. The improved durability of the AAA electrode enables our CIGS solar cells to maintain ∼95% of their initial power conversion efficiency, following 1000 bending cycles. In comparison, devices fabricated using AZO and ITO electrodes are only able to maintain ∼57 and ∼5%, respectively, due to crack formation and delamination of the films. This AAA sandwich structure electrode could therefore serve as a high-performance electrode for numerous flexible optoelectronic applications.

A facile wet soaking process by immersing a CIGS thin film in a mixed aqueous solution, containing gallium trichloride and thioacetamide at 80 °C for a few tens of seconds, was proposed to reduce the existence of defects in the CIGS absorption layer which can be confirmed by the temperature dependence of the open-circuit voltage (Voc). The depth profiles of X-ray photoelectron spectroscopy (XPS) results indicate that the gallium (Ga) concentration increases during the short wet soaking time, resulting in a widening of the band gap near the surface region. The enhanced carrier lifetime attributed to the Ga-induced defect reduction during thermal treatment of device fabrication was evaluated by time-resolved photoluminescence (TRPL) spectroscopy. With wet and light soaking processes, Voc, short circuit current (Jsc) and fill factor (F.F.) can be increased, yielding a significant enhancement in cell efficiency from ∼1% to ∼6.4%. We believe that this fast, simple and effective method can further stimulate the development of CBD-Zn(O,S)/post-selenization CIGS solar cells toward commercialized thin film photovoltaics.