High conductive ITO-free flexible electrode based on Gr-grafted-CNT/Au NPs for optoelectronic applications

Abstract The present work illustrates a simple and cheap solution-based technique for the preparation of high conductive and transparent electrode based on graphene/carbon nanotube/gold nanoparticles (Gr/CNT/Au NPs) replacing indium tin oxide (ITO). The prepared nanocomposite was applied as anode in flexible polymer solar cells (PSCs). Anode was prepared with spin-coating Gr/CNT/Au NPs solution on polyethylene terephthalate (PET) substrate. Functionalizing PET substrate guaranteed good adhesion of electrode to substrate and improved mechanical stability in bent condition. Thermal annealing was applied for 30 min and the highest transparency of 69% and lowest sheet resistance of 0.45 kΩ/sq was achieved. Photovoltaic parameters of prepared PSCs were analyzed with different Au NPs concentration in bent and rest condition. Sheet resistance and photovoltaic results confirmed that 17 W% CNT and 15 V% Au NPs solution had the highest short circuit current density (Jsc = 3.1 mA/cm2), open circuit voltage (Voc = 1.0 V) and power conversion efficiency (PCE = 0.55%), and showed 139% improvement to Gr/CNT based devices. At 45° of bending, photovoltaic parameters have not changed and it showed excellent mechanical stability of fabricated electrode. Impedance analysis revealed that after Au NPs addition resistance losses between anode and buffer layer decreases from 748 Ω to 423 Ω in GC17 and GCA15 respectively, which shows facilitated charge transfer and reduced charge recombination. Advantages of fabricated electrode is simple process of preparation using solution based technique, environmentally friendly method, excellent mechanical stability and high conductivity and transparency which makes the proposed electrode suitable for roll-to-roll production in optoelectronic devices.