Solution-Processed Electron-Transport Layer-Free Organic Photovoltaics with Liquid Metal Cathodes

Solution-processed organic photovoltaics (OPVs) are<b> </b>promising renewable energy devices because of their energy-saving process technology and high throughput rate. The power conversion efficiency (PCE) of solution-processed active materials highlights their potential applications as an energy-harvesting power source for self-powered e-skin devices or biosensors for the detection of electrophysiological signals. In addition to the<b> </b>appropriate fabrication of active and charge transport layers, the development of printed electrodes has attracted considerable research attention. Numerous printable materials have been developed to replace the conventional evaporated top electrodes. However, achieving fully or partially solution-processed OPVs with PCEs comparable to those of OPVs with vacuum-deposited transparent and top electrodes is challenging because of the difficulty of forming a uniform interface between the top solution-processed electrode and active layer. In this study, we investigated the PCE of solution-processed OPVs by using an electron<b>-</b>transport layer-free eutectic gallium–indium (EGaIn) cathode. The direct coating of EGaIn on the active layer in a nitrogen atmosphere is conducive for energy band matching and obtaining physically perfect interfaces without any penetration or voids. An average PCE of 14.1% and enhanced operating stability comparable to conventional OPVs were achieved with indium tin oxide transparent electrodes. The fully solution-processed flexible OPVs fabricated with the embedded silver nanowire strategy in ultrathin transparent polyimide achieved an average PCE of 12.7%, representing a promising technique to meet such clean and high-throughput energy demand.