Novel Cathode Interlayers Based on Neutral Alcohol-Soluble Small Molecules with a Triphenylamine Core Featuring Polar Phosphonate Side Chains for High-Performance Polymer Light-Emitting and Photovoltaic Devices

A new family of neutral alcohol‐soluble small molecular materials comprised of electron‐rich triphenylamine (TPA) and fluorene featuring phosphonate side chains (FEP) is reported, namely 3TPA‐FEP, 2TPA‐2FEP and TPA‐3FEP, which have different TPA and FEP contents. Due to their good solubility in polar solvents like alcohol, multilayer devices can be fabricated by a wet process from orthogonal solvents. Polymer light‐emitting devices with these materials as a cathode interlayer and Al as the cathode show greatly enhanced efficiencies in contrast to control devices without such a cathode interlayer, and their efficiencies are comparable with or even higher than devices with the low work‐function metal Ba/Al as the cathode. In addition, high‐performance polymer solar cells based on the poly[N‐9''‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(4',7'‐di‐2‐thienyl‐2',1',3'‐benzothiadiazole)] (PCDTBT):[6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) system are also achieved with power conversion efficiencies of 7.21%, 6.90% and 6.89%, by utilizing 3TPA‐FEP, 2TPA‐2FEP and TPA‐3FEP as the cathode interlayer, respectively. These efficiencies are also much higher than those for control devices without the cathode interlayer. Although TPA is well‐known as a hole‐transport unit, the current findings indicate that alcohol‐soluble TPA‐based small molecules are also a promising cathode interlayer for both electron injection and extraction. A family of neutral alcohol‐soluble small molecular materials based on an electron‐rich triphenylamine (TPA) core featuring polar phosphonate side chains is developed as an excellent cathode interlayer for polymer light‐emitting and photovoltaic devices. Although TPA is well‐known as a hole‐transporting unit, the current findings indicate that the TPA‐based alcohol‐soluble small molecules are also a promising cathode interlayer for high performance optoelectronic devices.