ITO-free inverted polymer solar cells using a GZO cathode modified by ZnO

A gallium-doped ZnO (GZO) layer was investigated and compared with a conventional indium-tin-oxide (ITO) layer for use as a cathode in an inverted polymer solar cell based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ). By modifying the GZO cathode with a ZnO thin layer, a high power conversion efficiency (3.4%) comparable to that of an inverted solar cell employing the same P3HT:PCBM BHJ photoactive layer with a conventional ITO/ZnO cathode was achieved. This result indicates that GZO is a transparent electrode material that can potentially be used to replace high-cost ITO.

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► ITO-free inverted polymer solar cells using a Ga-doped ZnO (GZO) cathode modified by ZnO.
► Similar band structure and compatibility between ZnO and GZO.
► Inverted polymer solar cells with either ZnO/GZO or ZnO/ITO have comparable PCEs despite the relatively high sheet resistance and low optical transparency of the GZO.