Optimized Graphene-Oxide-Based Interconnecting Layer in All-Perovskite Tandem Solar Cells.

All-perovskite tandem solar cells represent a significant advancement in next-generation photovoltaics toward higher power conversion efficiencies than single junction cells. A critical component of a monolithic tandem solar cell is the interconnecting layer, which facilitates the integration of the wide bandgap and low bandgap subcells. Conventional designs in all-perovskite tandem cells are based on an ultrathin metal recombination layer, typically Au, alongside a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transporting layer, which introduce optical and recombination losses, and instabilities. Here, we present a new interconnecting layer based on a graphene-oxide recombination layer, which facilitates the replacement of PEDOT:PSS with the preferred self-assembled monolayer [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz). This device architecture results in significantly reduced optical and nonradiative losses, leading to champion device efficiency of 23.4% compared to 19.7% with the conventional layers, along with improvements in stability. This work solves a critical challenge in all-perovskite tandem cell device design.