Nanograting Structured Ultrathin Substrate for Ultraflexible Organic Photovoltaics

The nanopatterning of the surfaces of polymer substrates enhances the performances of photovoltaics. Ultraflexible organic photovoltaics (OPVs) are one of the promising energy harvesters for wearable electronics. A reduction in incident light angle dependence while maintaining the power conversion efficiency (PCE) is desirable for wearable electronics devices in which the angle of incident light continuously changes due to the deformation of the device. However, the nanopatterning of the ultrathin polymer substrates of ultraflexible OPVs using the reported methods is challenging because they fatally damage the substrates. Here, the fabrication of ultraflexible OPVs having a low incident light angle dependence while maintaining a PCE of 10.5% by developing ultrathin nanograting polymer substrates is reported. The nanograting-patterned fluorinated polymer enables the formation of periodic nanograting structures onto the back surface of a 1 µm thick polymer substrate having a pitch of 760 nm and a height of 100 nm, while the opposite surface remains flat after the formation of the planarization layer. Furthermore, with the nanopatterning of the ultrathin substrate, electron-transporting layer, and active layer, the ultraflexible OPVs exhibit a PCE of 10.8%. The combination of new materials with the developed patterning method is expected to afford even greater performances.