Enhanced optoelectronic coupling for perovskite-silicon tandem solar cells

Monolithic perovskite/silicon tandem solar cells are of great appeal as they promise high power conversion efficiencies (PCEs) at affordable cost. In state-of-the-art tandems, the perovskite top cell is electrically coupled to a silicon heterojunction bottom cell via a self-assembled monolayer (SAM), anchored on a transparent conductive oxide (TCO), which enables efficient charge transfer between the subcells.1-3 Yet, reproducible high-performance tandem solar cells require energetically homogenous SAM coverage, which remains challenging, especially on textured silicon bottom cells. Here, we resolve this issue by employing ultrathin (5 nm) amorphous indium zinc oxide (IZO) as the interconnecting TCO, exploiting its high surface-potential homogeneity resulting from the absence of crystal grains, and higher density of SAM anchoring sites when compared to commonly employed crystalline TCOs. Combined with optical enhancements via equally thin IZO rear electrodes and improved front contact stacks, an independently certified PCE of 32.5% was obtained, which ranks amongst the highest for perovskite/silicon tandems. Our ultrathin transparent contact approach reduces indium consumption by approximately 80%, which is of importance towards sustainable PV manufacturing.