Mechanical Stability Study on PEDOT:PSS-Based ITO-Free Flexible Perovskite Solar Cells

Flexible perovskite solar cells (FPSCs) have emerged rapidly due to their promising applications in various fields such as portable electronic devices, building-integrated photovoltaics, unmanned systems, and so on. Although plenty of studies on FPSCs have been reported, most of them focused on the improvement of power conversion efficiency (PCE) while scarcely on the mechanical stability. Herein, we report an in-depth analysis of the mechanical stability of PEDOT:PSS (Clevios PH1000, abbreviated as PH1000) transparent conductive electrode-based FPSCs. The nanoindentation technique is used to acquire the mechanical properties of each layer in the devices, and the finite element method (FEM) is then used to calculate the von Mises stress distribution within the devices under different bending conditions. Correspondingly, a scanning electron microscope is used to observe the morphological changes in the devices before and after the bending test. Due to the high stress distribution within the ITO layer, evident cracks are observed in the ITO layer after cyclic bending, which increases its electric resistance sharply and leads to the rapid deterioration of the photovoltaic performance of the devices. Compared to the PET-ITO counterpart, the PH1000 film exhibits excellent flexibility without any cracks and an obvious increase of resistance after bending due to its low stress. However, under a small bending radius (2 mm), the high stress in the MAPbI3 film also leads to obvious cracks and thus results in the deterioration of device performance.