Top Illuminated Hysteresis-Free Perovskite Solar Cells Incorporating Microcavity Structures on Metal Electrodes: A Combined Experimental and Theoretical Approach.

Further technological development of perovskite solar cells (PSCs) will require improvements in power conversion efficiency and stability, while maintaining low material costs and simple fabrication. In this Research Article, we describe top-illuminated ITO-free, stable PSCs featuring microcavity structures, wherein metal layers on both sides on the active layers exerted light interference effects in the active layer, potentially increasing the light path length inside the active layer. The optical constants (refractive index and extinction coefficient) of each layer in the PSC devices were measured, while the optical field intensity distribution was simulated using the transfer matrix method. The photocurrent densities of perovskite layers of various thicknesses were also simulated; these results mimic our experimental values exceptionally well. To modify the cavity electrode surface, we deposited a few nanometers of ultrathin MoO3 (2, 4, and 6 nm) in between the Ag and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) layers provide hydrophobicity to the Ag surface and elevate the work function of Ag to match that of the hole transport layer. We achieved a power conversion efficiency (PCE) of 13.54% without hysteresis in the device containing a 4 nm-thick layer of MoO3. In addition, we fabricated these devices on various cavity electrodes (Al, Ag, Au, Cu); those prepared using Cu and Au anodes displayed improved device stability of up to 72 days. Furthermore, we prepared flexible PSCs having a PCE of 12.81% after incorporating the microcavity structures onto poly(ethylene terephthalate) as the substrate. These flexible solar cells displayed excellent stability against bending deformation, maintaining greater than 94% stability after 1000 bending cycles and greater than 85% after 2500 bending cycles performed with a bending radius of 5 mm.