High figure-of-merit Ag/Al:ZnO nano-thick transparent electrodes for indium-free flexible photovoltaics

We propose a novel transparent electrode consisting of silver (Ag)–aluminum doped zinc oxide (AZO)–nickel (Ni) deposited at room temperature on glass and polyethylene terephthalate (PET) for flexible organic photovoltaics. The electrode combines the high electrical conductivity and mechanical ductility of Ag, the transparency and antireflection of AZO and the high work function and stability of Ni. Environmental stability results confirmed that the electrode maintains its optical and electrical properties at both elevated temperature (500 °C) and under damp heat conditions (85 °C and 85% relative humidity). To demonstrate its functional potential, the electrode has been used as the transparent anode in an organic solar cell (OSC), which shows an efficiency of 2.6%, very close to the value (2.9%) obtained in a similar cell using the widely used indium tin oxide (ITO). With respect to ITO, the proposed transparent electrode has several advantages, including mechanical flexibility, room temperature processing and low cost.

► Transparent electrodes (TEs) made of Ag/AZO films were prepared by sputtering at room temperature. ► Ag(11)/AZO(30) has a figure-of-merit larger than other TEs. ► The proposed electrodes are stable against elevated temperature and damp heat conditions. ► Ag/AZO was used as TE in an OSC achieving >90% of the efficiency of a similar device incorporating ITO. ► Sheet resistance of the proposed electrode remains unchanged even after 104 bending cycles.