Transparent and flexible amorphous InZnAlO films grown by roll-to-roll sputtering for acidic buffer-free flexible organic solar cells

• Roll-to-roll sputtered InZnAlO film was investigated as a transparent anode for flexible organic photovoltaics.
• The Al and Zn doping into In2O3 matrix led to amorphous structure of the InZnAlO films.
• Amorphous IZAO films eliminate the use of acidic PEDOT:PSS layer for flexible organics photovoltaics.

We report on transparent and flexible amorphous In–Zn–Al–O (a-IZAO) films prepared by roll-to-roll (RTR) sputtering for use as anodes in acidic buffer free flexible organic solar cells (FOSCs). The presence of Zn and Al structural stabilizers in the In2O3 matrix produced a completely amorphous structure with the high optical transmittance of 89.25% and the low resistivity of 2.123 × 10−3 Ω-cm, as well as the high work function of 5.14 eV, making the a-IZAO films suitable for use as flexible anodes for FOSCs. In addition, the a-IZAO films showed no change in resistance (ΔR) during outer and inner bending fatigue tests due to their good mechanical flexibility. Relative to the power conversion efficiency (1.944%) of a PEDOT:PSS-based FOSCs, a FOSC fabricated by using an a-IZAO anode and without the use of acidic PEDOT:PSS buffer showed greater power conversion efficiency (2.509%), owing to the absence of interfacial reactions between the acidic PEDOT:PSS and the a-IZAO anode.

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