Organic Photovoltaic Devices Using an Amorphous Molecular Material With High Hole Drift Mobility, Tris[4-(2-thienyl)phenyl]amine

A planar p-n heterojunction organic photovoltaic (OPV) device using an amorphous molecular material with a high hole drift mobility of 1.1 × 10^-2 cm²/V·s at an electric field of 1.0 × 10⁵ V/cm at 293 K, tris[4-(2-thienyl)phenyl]amine (TTPA), as an electron donor, and C₆₀, as an electron acceptor, indium-tinoxide (ITO)/poly(3,4-ethylenedioxythiophene) doped with poly(4-styrene sulfonate) (PEDOT:PSS) (ca.30 nm)/TTPA (30 nm)/C₆₀ (40 nm)/LiF (0.1 nm)/Al (150 nm), exhibited high performance with a fill factor of 0.62 and a power conversion efficiency (PCE) of 1.5 % under air-mass 1.5G illumination at an intensity of 100 mW/cm². A p-i-n-type OPV device having a mixed interlayer of TTPA and C₆₀, ITO/PEDOT (ca.30 nm)/TTPA (27 nm)/TTPA:C₆₀ (1:4 molar ratio, 20 nm)/C₆₀ (23 nm)/LiF (0.1 nm)/Al (100 nm), exhibited higher performance with a PCE of 1.8% under the same irradiation conditions. A bulk p-n heterojunction OPV devices fabricated by spin coating from solution of TTPA and [6,6]-phenyl-C₆₁-butyric acid methyl ester ([6,6]-PCBM), ITO/PEDOT:PSS (ca. 30 nm)/TTPA:[6,6]-PCBM (1:4 molar ratio, ca. 73 nm)/LiF (0.1 nm)/Al (100 nm), exhibited a PCE of 1.3%. The high performance of the present devices is attributed to the high charge-carrier mobilities of the materials and the relatively high ionization potential of TTPA.