Complementary Absorbing Star‐Shaped Small Molecules for the Preparation of Ternary Cascade Energy Structures in Organic Photovoltaic Cells

Two anthracene‐based star‐shaped conjugated small molecules, 5′,5″‐(9,10‐bis((4‐hexylphenyl)ethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), HBantHBT, and 5′,5″‐(9,10‐bis(phenylethynyl)anthracene‐2,6‐diyl)bis(5‐hexyl‐2,2′‐bithiophene), BantHBT, are used as electron‐cascade donor materials by incorporating them into organic photovoltaic cells prepared using a poly((5,5‐E‐alpha‐((2‐thienyl)methylene)‐2‐thiopheneacetonitrile)‐alt‐2,6‐[(1,5‐didecyloxy)naphthalene])) (PBTADN):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC 71 BM) blend. The small molecules penetrate the PBTADN:PC 71 BM blend layer to yield complementary absorption spectra through appropriate energy level alignment and optimal domain sizes for charge carrier transfer. A high short‐circuit current ( J SC ) and fill factor (FF) are obtained using solar cells prepared with the ternary blend. The highest photovoltaic performance of the PBTADN: BantHBT :PC 71 BM blend solar cells is characterized by a J SC of 11.0 mA cm −2 , an open circuit voltage ( V OC ) of 0.91 V, a FF of 56.4%, and a power conversion efficiency (PCE) of 5.6% under AM1.5G illumination (with a high intensity of 100 mW −2 ). The effects of the small molecules on the ternary blend are investigated by comparison with the traditional poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC 61 BM) system.