Efficient All‐Perovskite Tandem Solar Cells with Low‐Optical‐Loss Carbazolyl Interconnecting Layers

Abstract Combining wide‐band gap (WBG) and narrow‐band gap (NBG) perovskites with interconnecting layers (ICLs) to construct monolithic all‐perovskite tandem solar cell is an effective way to achieve high power conversion efficiency (PCE). However, optical losses from ICLs need to be further reduced to leverage the full potential of all‐perovskite tandem solar cells. Here, metal oxide nanocrystal layers anchored with carbazolyl hole‐selective‐molecules (CHs), which exhibit much lower optical loss, is employed to replace poly(3,4‐ethylenedioxythiophene) polystyrenesulfonate (PEDOT : PSS) as the hole transporting layers (HTLs) in lead‐tin (Pb‐Sn) perovskite sub‐cells and ICLs in all‐perovskite tandem solar cells. Optically transparent indium tin oxide nanocrystals (ITO NCs) layers are employed to enhance anchoring of CHs, while a mixture of two CHs is adopted to tune the surface energy‐levels of ITO NCs. The optimized mixed Pb‐Sn NBG perovskite solar cells demonstrate a high PCE of 23.2 %, with a high short‐circuit current density ( J sc ) of 33.5 mA cm −2 . A high PCE of 28.1 % is further obtained in all‐perovskite tandem solar cells, with the highest J sc of 16.7 mA cm −2 to date. Encapsulated tandem solar cells maintain 90 % of their reference point after 500 h of operation at the maximum power point (MPP) under 1‐Sun illumination.