Organic Single-Crystalline Donor–Acceptor Heterojunctions with Ambipolar Band-Like Charge Transport for Photovoltaics

Solution-processed organic single-crystalline donor–acceptor heterojunctions (SCHJs) composed of N,N,N′,N′-tetraphenylbenzidine (TPB) and phenyl-C₆₁-butyric acid methyl ester ([60]PCBM) are successfully obtained, and fundamental studies on its charge transport properties are demonstrated, revealing the advantages of applying SCHJs in photovoltaic devices. The SCHJs exhibit a balanced high-mobility ambipolar charge transport with both hole and electron mobility being more than one-order magnitude higher than its thin-film heterojunction (TFHJ) counterparts. The difference between single-crystalline and TFHJs in charge transport mechanisms was revealed, and it is shown that SCHJs present a more favorable band-like charge transport properties at room temperature. Organic photovoltaics fabricated on SCHJs present much higher current density and a 32-times higher power conversion efficiencies than TFHJ devices. The present work, which outlines comprehensive advantages of SCHJs in charge transport properties, should accelerate the application of organic single crystals for high-performance photovoltaics.