Low-Cost N,N″-Bicarbazole-Based Dopant-Free Hole-Transporting Materials for Large-Area Perovskite Solar Cells

Despite the recent unprecedented development of efficient dopant-free hole transporting materials (HTMs) for high-performance perovskite solar cells (PSCs) on small-area devices (≤0.1 cm²), low-cost dopant-free HTMs for large-area PSCs (≥1 cm²) with high power conversion efficiencies (PCEs) have rarely been reported. Herein, two novel HTMs, 3,3′,6,6′ (or 2,2′,7,7′)-tetrakis(N,N′-di-p-methoxyphenylamine)-N,N′-bicarbazole (3,6 BCz-OMeTAD or 2,7 BCz-OMeTAD), are synthesized via an extremely simple route from very cheap raw materials. Owing to their excellent film-forming abilities and matching energy levels, 3,6 BCz-OMeTAD and 2,7 BCz-OMeTAD can be successfully employed as a perfect ultrathin (≈30 nm) hole transporting layer in large-area PSCs up to 1 cm². The 3,6 BCz-OMeTAD and 2,7 BCz-OMeTAD based large-area PSCs show highest PCEs up to 17.0% and 17.6%, respectively. More importantly, high performance large-area PSCs based on 2,7 BCz-OMeTAD retain 90% of the initial efficiency after 2000 h storage in an ambient environment without encapsulation.