Stable Inverted Planar Perovskite Solar Cells with Low‐Temperature‐Processed Hole‐Transport Bilayer

Low‐temperature‐processed perovskite solar cells (PSCs), which can be fabricated on rigid or flexible substrates, are attracting increasing attention because they have a wide range of potential applications. In this study, the stability of reduced graphene oxide and the ability of a poly(triarylamine) underlayer to improve the quality of overlying perovskite films to construct hole‐transport bilayer by means of a low‐temperature method are taken advantage of. The bilayer is used in both flexible and rigid inverted planar PSCs with the following configuration: substrate/indium tin oxide/reduced graphene oxide/polytriarylamine/CH3NH3PbI3/PCBM/bathocuproine/Ag (PCBM = [6,6]‐phenyl‐C61‐butyric acid methyl ester). The flexible and rigid PSCs show power conversion efficiencies of 15.7 and 17.2%, respectively, for the aperture area of 1.02 cm2. Moreover, the PSC based the bilayer shows outstanding light‐soaking stability, retaining ≈90% of its original efficiency after continuous illumination for 500 h at 100 mW cm−2.