Optimised graphene-oxide-based interconnecting layer in all-perovskite tandem solar cells

All-perovskite tandem solar cells represent a significant advancement in next-generation photovoltaics towards 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):polystyrene sulfonate (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-(9Hcarbazol-9-yl) ethyl]phosphonic acid (2PACz). This device architecture results in significantly reduced optical and non-radiative 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.