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

Abstract

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 MoO (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 MoO. 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.

PEDOT:PSS for Flexible and Stretchable Electronics: Modifications, Strategies, and Applications

“…The flexible solar cells also showed high stability against bending deformations, retaining 90% of the original PCE for 1000 bending cycles and 85% for 5000 bending cycles at r of 2 mm. Chu et al fabricated the flexible PSC devices through the deposition of ultrathin MoO 3 layers on PEDOT:PSS HTLs. Introducing the ultrathin MoO 3 layer resulted in the alignment of energy levels and efficient charge‐carrier extraction.…”

Recent Progress on Advanced Optical Structures for Emerging Photovoltaics and Photodetectors

“…To realize semitransparency in OPVs and PSCs, one can manipulate the coverage, [ 35–43,161–163 ] thickness, [ 10–17,44–48,164,165 ] or bandgap of the active layer [ 2,8,9,18–24,49,50,166–168 ] or replace the opaque metal electrode with light‐transmitting media (e.g., metal nanowires, [ 44,46,51–56,169–171 ] transparent conducting oxides, [ 43,57–61,167,168,172–180 ] transparent conducting polymers, [ 40,62,63,181–184 ] graphene, [ 54,64,164,185 ] and carbon nanotube [ 65,186–188 ] ). Although the most convenient way to fabricate an ST‐PV is to decrease the thickness of the top metal electrode and, thereby, increase its transparency, [ 35,39,40,47,58,66–72,124 ] there is always a trade‐off between conductivity and transparency. By sandwiching a thin metal film between dielectric layers, decent electrical and optical properties can be achieved.…”

“…By sandwiching a thin metal film between dielectric layers, decent electrical and optical properties can be achieved. [ 73,74,117,124 ]…”

Recent Advances of Organic Solar Cells with Optical Microcavities

“…MCs are used not only in organic‐based solar cells, but also in perovskite‐based solar cells . Lu et al fabricated semitransparent, color‐adjustable perovskite solar cells using Ag/ITO/Ag MC electrodes .…”

“…In addition, the device has good stability, and its efficiency remains high after 70 days in glove box. Lai and Chu et al fabricated a top‐illuminated MC perovskite solar cell without hysteresis . As shown in Figure , by inserting a layer of MoO 3 between the HTL and the metal electrode, the surface of Ag is effectively modified, and the work function of Ag is improved to match the HTL better.…”