Transferable transparent electrodes of liquid metals for bifacial perovskite solar cells and heaters

Despite the significant advantages of liquid metals, such as outstanding mechanical deformability and good electrical conductivity, their intrinsic opacity and unsuitability for conventional photolithography processing have limited their extensive utilization for transparent conductive films. Herein, we present the formation of transparent and stretchable electrodes of liquid metals using a direct printing method with high resolutions. Conductive grid structures of liquid metals can be printed directly at room temperature with linewidth below 5 µm with no additional processing, and they exhibit superb optoelectronic properties (low sheet resistance of 1.7 Ω sq⁻¹ at high transmittance of 90.1%). Also, after their encapsulation with an elastomeric layer, these fine grid patterns are transferrable from printed regions onto various nonplanar surfaces. In addition, the bifacial perovskite solar cells fabricated using these transparent electrodes have high power conversion efficiency, i.e., 14.12%, with an outstanding bifaciality factor of 81.09%. In addition, these fine grids of liquid metals can be operated as transparent heaters that operate reliably and have rapid heating rates even in the extremely cold environment of − 30 °C, which is significantly lower than their melting temperature (15.5 °C). Thus, their use may be a promising strategy for next-generation free-form electronics and automobile applications.