Organic Thin‐film Solar Cells Using Benzotrithiophene Derivatives Bearing Acceptor Units as Non‐Fullerene Acceptors

New star‐shaped non‐fullerene acceptors (5 Z ,5′ Z ,5′′ Z )‐5,5′,5′′‐((benzo[1,2‐ b  : 3,4‐ b′  : 5,6‐ b′′ ]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐2‐thioxothiazolidin‐4‐one) ( 1 : BTT‐OT‐ORD) and 2,2′,2′′‐((5 Z ,5′ Z ,5′′ Z )‐((benzo[1,2‐ b  : 3,4‐ b′  : 5,6‐ b′′ ]trithiophene‐2,5,8‐triyltris(4‐octylthiophene‐5,2‐diyl))tris(methaneylylidene))tris(3‐octyl‐4‐oxothiazolidine‐5,2‐diylidene))trimalononitrile ( 2 : BTT‐OT‐OTZDM) with a benzotrithiophene core, alkyl‐thiophen units, and acceptor units were designed and synthesized. The HOMO‐LUMO levels of 1 and 2 were determined by photoemission spectroscopy and UV‐Vis absorption spectroscopy. Binary blend and ternary blend bulk heterojunction (BHJ) organic solar cells with non‐fullerene acceptors 1 and 2 were fabricated with the inverted device structures of glass/ITO/ZnO/active_layer/MoO 3 /Ag. Both binary blend BHJ solar cells with 1 and 2 show lower J SC and larger V OC values than P3HT : PCBM solar cells. On the other hand, ternary blend BHJ organic solar cells, including 10 % of 1 , exhibited a larger power conversion efficiency than P3HT : PCBM solar cells because the J SC value was largely improved.