Flexible Crystalline Silicon Photovoltaics with Vertically Aligned Microwires

Abstract

Flexible photovoltaics (FPVs) are one of the most promising research fields in the solar energy industry because they can be utilized as a continous power source for wearable and portable electronic devices. Thin crystalline silicon (c-Si) has attracted much attention as a potential means for FPVs because of its excellent flexibility while retaining the advantages of c-Si PVs of high efficiency and stability. For highly efficient thin c-Si FPVs, it is important to maximize light absorption while maintaining the flexibility characteristics. In general, the conventional c-Si photovoltaics have increased light absorption by applying surface structures. However, the surface structures without consideration of the flexibility would limit the flexibility of the FPVs because induced stress during bending cannot be uniformly dispersed. In this study, vertically aligned microwires (MWs) on a 50 μm-thick thin c-Si substrate are designed for novel FPVs. Increasing the length of the MWs enhances the optical properties of the thin c-Si without affecting its flexibility. To maximize the efficiency of the thin c-Si FPVs with MWs, tapered MWs and a localized back-contact structure are devised. This device shows a maximum efficiency of 18.9%. In addition, the proposed thin c-Si FPV with MWs shows high stability without any change in efficiency, even with 1000 bending cycles with a bending radius of 12 mm. Thus, we successfully demonstrate battery-free flexible electronic devices integrated with our thin c-Si FPVs with MWs.