Optimized\nGraphene-Oxide-Based Interconnecting Layer\nin All-Perovskite Tandem Solar Cells

All-perovskite tandem solar cells represent a significant\nadvancement\nin next-generation photovoltaics toward higher power conversion efficiencies\nthan single junction cells. A critical component of a monolithic tandem\nsolar cell is the interconnecting layer, which facilitates the integration\nof the wide bandgap and low bandgap subcells. Conventional designs\nin all-perovskite tandem cells are based on an ultrathin metal recombination\nlayer, typically Au, alongside a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate\n(PEDOT:PSS) hole transporting layer, which introduce optical and recombination\nlosses, and instabilities. Here, we present a new interconnecting\nlayer based on a graphene-oxide recombination layer, which facilitates\nthe replacement of PEDOT:PSS with the preferred self-assembled monolayer\n[2-(9<i>H</i>-carbazol-9-yl)ethyl]phosphonic acid (2PACz).\nThis device architecture results in significantly reduced optical\nand nonradiative losses, leading to champion device efficiency of\n23.4% compared to 19.7% with the conventional layers, along with improvements\nin stability. This work solves a critical challenge in all-perovskite\ntandem cell device design.