Compact-porous hole-transport-layer for highly efficient near-infrared region transparent perovskite solar cells for tandem applications

Wide-bandgap perovskites solar cells (PSCs) are vital as top cells in perovskite-based tandem solar cells (TSCs). However, poor band alignment with the charge transport layer and unwanted parasitic absorption in the top semitransparent-PSC (ST-PSC) are major factors limiting the power conversion efficiency (PCE) of TSCs. Herein, we present a compact-porous nickel oxide (cp-NiO_x) hole-transport layer (HTL) sequentially fabricated using a sol-gel suspension and colloidal suspension of highly crystalline NiO_x. The cp-NiO_x film exhibited enhanced transparency, mesoporous surface morphology, and better energy band alignment with a 1.68 eV perovskite film for fabricating highly near-infrared transparent (∼92 % (@800–1200 nm)) ST-PSCs. The best cell achieved a PCE of 15.9 %. In addition, a four-terminal perovskite/silicon TSC based on the cp-NiO_x HTL achieved an outstanding PCE of ∼26.0 %. The tailored energy band structure and reduced parasitic absorption in the near-infrared region of the ST-PSCs based on the cp-NiO_x HTL enabled fabrication of highly efficient inverted ST-PSCs for perovskite/silicon TSCs.