Transfer-free graphene electrodes for super-flexible and semi-transparent perovskite solar cells fabricated under ambient air

Graphene has shown many advantages over the metal oxide transparent materials that serve as conventional electrodes in solar cells because graphene is more transparent, has greater stability, and is more mechanically flexible. Flexibility and semi-transparency of the perovskite solar cells are challenged to integrate with the flexible electronic devices since the perovskite solar cells have discovered. Herein, we provide the first report of transfer-free, large-scale monolayer graphene employed as a transparent and flexible bottom electrode. High-quality graphene without transfer process was directly synthesized at 150 °C on a polymer substrate via plasma assisted thermal chemical vapor deposition (PATCVD). Additionally, a highly transparent AZO/Ag/AZO (AAA) multilayer was utilized as a top counter electrode to create semi-transparent perovskite solar cells with a remarkable degree of mechanical flexibility. The 300 nm-thick perovskite solar cells with PATCVD-Graphene revealed a high transmittance of ~26% at a wavelength of 700 nm. The highest level of power conversion efficiency (PCE) (~14.2%) was recorded by an illumination from the bottom graphene side. After 1000 bending cycles under a tensile strain of 1.5%, the graphene-based devices maintained a level of PCE that was more than 90% greater than the initial reading. This superior bending robustness highlights the potential for non-transfer, graphene-based, perovskite photovoltaic material to establish a tandem structure for a foldable solar cell.